text: """
  Create SQL statements for QuerySets.
  
  The code in here encapsulates all of the SQL construction so that QuerySets
  themselves do not have to (and could be backed by things other than SQL
  databases). The abstraction barrier only works one way: this module has to know
  all about the internals of models in order to get the information it needs.
  """
  import copy
  import difflib
  import functools
  import inspect
  import sys
  import warnings
  from collections import Counter, namedtuple
  from collections.abc import Iterator, Mapping
  from itertools import chain, count, product
  from string import ascii_uppercase
  
  from django.core.exceptions import (
      EmptyResultSet, FieldDoesNotExist, FieldError,
  )
  from django.db import DEFAULT_DB_ALIAS, NotSupportedError, connections
  from django.db.models.aggregates import Count
  from django.db.models.constants import LOOKUP_SEP
  from django.db.models.expressions import BaseExpression, Col, F, OuterRef, Ref
  from django.db.models.fields import Field
  from django.db.models.fields.related_lookups import MultiColSource
  from django.db.models.lookups import Lookup
  from django.db.models.query_utils import (
      Q, check_rel_lookup_compatibility, refs_expression,
  )
  from django.db.models.sql.constants import INNER, LOUTER, ORDER_DIR, SINGLE
  from django.db.models.sql.datastructures import (
      BaseTable, Empty, Join, MultiJoin,
  )
  from django.db.models.sql.where import (
      AND, OR, ExtraWhere, NothingNode, WhereNode,
  )
  from django.utils.deprecation import RemovedInDjango40Warning
  from django.utils.functional import cached_property
  from django.utils.tree import Node
  
  __all__ = ['Query', 'RawQuery']
  
  
  def get_field_names_from_opts(opts):
      return set(chain.from_iterable(
          (f.name, f.attname) if f.concrete else (f.name,)
          for f in opts.get_fields()
      ))
  
  
  def get_children_from_q(q):
      for child in q.children:
          if isinstance(child, Node):
              yield from get_children_from_q(child)
          else:
              yield child
  
  
  JoinInfo = namedtuple(
      'JoinInfo',
      ('final_field', 'targets', 'opts', 'joins', 'path', 'transform_function')
  )
  
  
  class RawQuery:
      """A single raw SQL query."""
  
      def __init__(self, sql, using, params=None):
          self.params = params or ()
          self.sql = sql
          self.using = using
          self.cursor = None
  
          # Mirror some properties of a normal query so that
          # the compiler can be used to process results.
          self.low_mark, self.high_mark = 0, None  # Used for offset/limit
          self.extra_select = {}
          self.annotation_select = {}
  
      def chain(self, using):
          return self.clone(using)
  
      def clone(self, using):
          return RawQuery(self.sql, using, params=self.params)
  
      def get_columns(self):
          if self.cursor is None:
              self._execute_query()
          converter = connections[self.using].introspection.identifier_converter
          return [converter(column_meta[0])
                  for column_meta in self.cursor.description]
  
      def __iter__(self):
          # Always execute a new query for a new iterator.
          # This could be optimized with a cache at the expense of RAM.
          self._execute_query()
          if not connections[self.using].features.can_use_chunked_reads:
              # If the database can't use chunked reads we need to make sure we
              # evaluate the entire query up front.
              result = list(self.cursor)
          else:
              result = self.cursor
          return iter(result)
  
      def __repr__(self):
          return "<%s: %s>" % (self.__class__.__name__, self)
  
      @property
      def params_type(self):
          return dict if isinstance(self.params, Mapping) else tuple
  
      def __str__(self):
          return self.sql % self.params_type(self.params)
  
      def _execute_query(self):
          connection = connections[self.using]
  
          # Adapt parameters to the database, as much as possible considering
          # that the target type isn't known. See #17755.
          params_type = self.params_type
          adapter = connection.ops.adapt_unknown_value
          if params_type is tuple:
              params = tuple(adapter(val) for val in self.params)
          elif params_type is dict:
              params = {key: adapter(val) for key, val in self.params.items()}
          else:
              raise RuntimeError("Unexpected params type: %s" % params_type)
  
          self.cursor = connection.cursor()
          self.cursor.execute(self.sql, params)
  
  
  class Query(BaseExpression):
      """A single SQL query."""
  
      alias_prefix = 'T'
      subq_aliases = frozenset([alias_prefix])
  
      compiler = 'SQLCompiler'
  
      def __init__(self, model, where=WhereNode, alias_cols=True):
          self.model = model
          self.alias_refcount = {}
          # alias_map is the most important data structure regarding joins.
          # It's used for recording which joins exist in the query and what
          # types they are. The key is the alias of the joined table (possibly
          # the table name) and the value is a Join-like object (see
          # sql.datastructures.Join for more information).
          self.alias_map = {}
          # Whether to provide alias to columns during reference resolving.
          self.alias_cols = alias_cols
          # Sometimes the query contains references to aliases in outer queries (as
          # a result of split_exclude). Correct alias quoting needs to know these
          # aliases too.
          # Map external tables to whether they are aliased.
          self.external_aliases = {}
          self.table_map = {}     # Maps table names to list of aliases.
          self.default_cols = True
          self.default_ordering = True
          self.standard_ordering = True
          self.used_aliases = set()
          self.filter_is_sticky = False
          self.subquery = False
  
          # SQL-related attributes
          # Select and related select clauses are expressions to use in the
          # SELECT clause of the query.
          # The select is used for cases where we want to set up the select
          # clause to contain other than default fields (values(), subqueries...)
          # Note that annotations go to annotations dictionary.
          self.select = ()
          self.where = where()
          self.where_class = where
          # The group_by attribute can have one of the following forms:
          #  - None: no group by at all in the query
          #  - A tuple of expressions: group by (at least) those expressions.
          #    String refs are also allowed for now.
          #  - True: group by all select fields of the model
          # See compiler.get_group_by() for details.
          self.group_by = None
          self.order_by = ()
          self.low_mark, self.high_mark = 0, None  # Used for offset/limit
          self.distinct = False
          self.distinct_fields = ()
          self.select_for_update = False
          self.select_for_update_nowait = False
          self.select_for_update_skip_locked = False
          self.select_for_update_of = ()
          self.select_for_no_key_update = False
  
          self.select_related = False
          # Arbitrary limit for select_related to prevents infinite recursion.
          self.max_depth = 5
  
          # Holds the selects defined by a call to values() or values_list()
          # excluding annotation_select and extra_select.
          self.values_select = ()
  
          # SQL annotation-related attributes
          self.annotations = {}  # Maps alias -> Annotation Expression
          self.annotation_select_mask = None
          self._annotation_select_cache = None
  
          # Set combination attributes
          self.combinator = None
          self.combinator_all = False
          self.combined_queries = ()
  
          # These are for extensions. The contents are more or less appended
          # verbatim to the appropriate clause.
          self.extra = {}  # Maps col_alias -> (col_sql, params).
          self.extra_select_mask = None
          self._extra_select_cache = None
  
          self.extra_tables = ()
          self.extra_order_by = ()
  
          # A tuple that is a set of model field names and either True, if these
          # are the fields to defer, or False if these are the only fields to
          # load.
          self.deferred_loading = (frozenset(), True)
  
          self._filtered_relations = {}
  
          self.explain_query = False
          self.explain_format = None
          self.explain_options = {}
  
      @property
      def output_field(self):
          if len(self.select) == 1:
              select = self.select[0]
              return getattr(select, 'target', None) or select.field
          elif len(self.annotation_select) == 1:
              return next(iter(self.annotation_select.values())).output_field
  
      @property
      def has_select_fields(self):
          return bool(self.select or self.annotation_select_mask or self.extra_select_mask)
  
      @cached_property
      def base_table(self):
          for alias in self.alias_map:
              return alias
  
      def __str__(self):
          """
          Return the query as a string of SQL with the parameter values
          substituted in (use sql_with_params() to see the unsubstituted string).
  
          Parameter values won't necessarily be quoted correctly, since that is
          done by the database interface at execution time.
          """
          sql, params = self.sql_with_params()
          return sql % params
  
      def sql_with_params(self):
          """
          Return the query as an SQL string and the parameters that will be
          substituted into the query.
          """
          return self.get_compiler(DEFAULT_DB_ALIAS).as_sql()
  
      def __deepcopy__(self, memo):
          """Limit the amount of work when a Query is deepcopied."""
          result = self.clone()
          memo[id(self)] = result
          return result
  
      def get_compiler(self, using=None, connection=None):
          if using is None and connection is None:
              raise ValueError("Need either using or connection")
          if using:
              connection = connections[using]
          return connection.ops.compiler(self.compiler)(self, connection, using)
  
      def get_meta(self):
          """
          Return the Options instance (the model._meta) from which to start
          processing. Normally, this is self.model._meta, but it can be changed
          by subclasses.
          """
          return self.model._meta
  
      def clone(self):
          """
          Return a copy of the current Query. A lightweight alternative to
          to deepcopy().
          """
          obj = Empty()
          obj.__class__ = self.__class__
          # Copy references to everything.
          obj.__dict__ = self.__dict__.copy()
          # Clone attributes that can't use shallow copy.
          obj.alias_refcount = self.alias_refcount.copy()
          obj.alias_map = self.alias_map.copy()
          obj.external_aliases = self.external_aliases.copy()
          obj.table_map = self.table_map.copy()
          obj.where = self.where.clone()
          obj.annotations = self.annotations.copy()
          if self.annotation_select_mask is None:
              obj.annotation_select_mask = None
          else:
              obj.annotation_select_mask = self.annotation_select_mask.copy()
          # _annotation_select_cache cannot be copied, as doing so breaks the
          # (necessary) state in which both annotations and
          # _annotation_select_cache point to the same underlying objects.
          # It will get re-populated in the cloned queryset the next time it's
          # used.
          obj._annotation_select_cache = None
          obj.extra = self.extra.copy()
          if self.extra_select_mask is None:
              obj.extra_select_mask = None
          else:
              obj.extra_select_mask = self.extra_select_mask.copy()
          if self._extra_select_cache is None:
              obj._extra_select_cache = None
          else:
              obj._extra_select_cache = self._extra_select_cache.copy()
          if self.select_related is not False:
              # Use deepcopy because select_related stores fields in nested
              # dicts.
              obj.select_related = copy.deepcopy(obj.select_related)
          if 'subq_aliases' in self.__dict__:
              obj.subq_aliases = self.subq_aliases.copy()
          obj.used_aliases = self.used_aliases.copy()
          obj._filtered_relations = self._filtered_relations.copy()
          # Clear the cached_property
          try:
              del obj.base_table
          except AttributeError:
              pass
          return obj
  
      def chain(self, klass=None):
          """
          Return a copy of the current Query that's ready for another operation.
          The klass argument changes the type of the Query, e.g. UpdateQuery.
          """
          obj = self.clone()
          if klass and obj.__class__ != klass:
              obj.__class__ = klass
          if not obj.filter_is_sticky:
              obj.used_aliases = set()
          obj.filter_is_sticky = False
          if hasattr(obj, '_setup_query'):
              obj._setup_query()
          return obj
  
      def relabeled_clone(self, change_map):
          clone = self.clone()
          clone.change_aliases(change_map)
          return clone
  
      def _get_col(self, target, field, alias):
          if not self.alias_cols:
              alias = None
          return target.get_col(alias, field)
  
      def rewrite_cols(self, annotation, col_cnt):
          # We must make sure the inner query has the referred columns in it.
          # If we are aggregating over an annotation, then Django uses Ref()
          # instances to note this. However, if we are annotating over a column
          # of a related model, then it might be that column isn't part of the
          # SELECT clause of the inner query, and we must manually make sure
          # the column is selected. An example case is:
          #    .aggregate(Sum('author__awards'))
          # Resolving this expression results in a join to author, but there
          # is no guarantee the awards column of author is in the select clause
          # of the query. Thus we must manually add the column to the inner
          # query.
          orig_exprs = annotation.get_source_expressions()
          new_exprs = []
          for expr in orig_exprs:
              # FIXME: These conditions are fairly arbitrary. Identify a better
              # method of having expressions decide which code path they should
              # take.
              if isinstance(expr, Ref):
                  # Its already a Ref to subquery (see resolve_ref() for
                  # details)
                  new_exprs.append(expr)
              elif isinstance(expr, (WhereNode, Lookup)):
                  # Decompose the subexpressions further. The code here is
                  # copied from the else clause, but this condition must appear
                  # before the contains_aggregate/is_summary condition below.
                  new_expr, col_cnt = self.rewrite_cols(expr, col_cnt)
                  new_exprs.append(new_expr)
              else:
                  # Reuse aliases of expressions already selected in subquery.
                  for col_alias, selected_annotation in self.annotation_select.items():
                      if selected_annotation is expr:
                          new_expr = Ref(col_alias, expr)
                          break
                  else:
                      # An expression that is not selected the subquery.
                      if isinstance(expr, Col) or (expr.contains_aggregate and not expr.is_summary):
                          # Reference column or another aggregate. Select it
                          # under a non-conflicting alias.
                          col_cnt += 1
                          col_alias = '__col%d' % col_cnt
                          self.annotations[col_alias] = expr
                          self.append_annotation_mask([col_alias])
                          new_expr = Ref(col_alias, expr)
                      else:
                          # Some other expression not referencing database values
                          # directly. Its subexpression might contain Cols.
                          new_expr, col_cnt = self.rewrite_cols(expr, col_cnt)
                  new_exprs.append(new_expr)
          annotation.set_source_expressions(new_exprs)
          return annotation, col_cnt
  
      def get_aggregation(self, using, added_aggregate_names):
          """
          Return the dictionary with the values of the existing aggregations.
          """
          if not self.annotation_select:
              return {}
          existing_annotations = [
              annotation for alias, annotation
              in self.annotations.items()
              if alias not in added_aggregate_names
          ]
          # Decide if we need to use a subquery.
          #
          # Existing annotations would cause incorrect results as get_aggregation()
          # must produce just one result and thus must not use GROUP BY. But we
          # aren't smart enough to remove the existing annotations from the
          # query, so those would force us to use GROUP BY.
          #
          # If the query has limit or distinct, or uses set operations, then
          # those operations must be done in a subquery so that the query
          # aggregates on the limit and/or distinct results instead of applying
          # the distinct and limit after the aggregation.
          if (isinstance(self.group_by, tuple) or self.is_sliced or existing_annotations or
                  self.distinct or self.combinator):
              from django.db.models.sql.subqueries import AggregateQuery
              outer_query = AggregateQuery(self.model)
              inner_query = self.clone()
              inner_query.select_for_update = False
              inner_query.select_related = False
              inner_query.set_annotation_mask(self.annotation_select)
              if not self.is_sliced and not self.distinct_fields:
                  # Queries with distinct_fields need ordering and when a limit
                  # is applied we must take the slice from the ordered query.
                  # Otherwise no need for ordering.
                  inner_query.clear_ordering(True)
              if not inner_query.distinct:
                  # If the inner query uses default select and it has some
                  # aggregate annotations, then we must make sure the inner
                  # query is grouped by the main model's primary key. However,
                  # clearing the select clause can alter results if distinct is
                  # used.
                  has_existing_aggregate_annotations = any(
                      annotation for annotation in existing_annotations
                      if getattr(annotation, 'contains_aggregate', True)
                  )
                  if inner_query.default_cols and has_existing_aggregate_annotations:
                      inner_query.group_by = (self.model._meta.pk.get_col(inner_query.get_initial_alias()),)
                  inner_query.default_cols = False
  
              relabels = {t: 'subquery' for t in inner_query.alias_map}
              relabels[None] = 'subquery'
              # Remove any aggregates marked for reduction from the subquery
              # and move them to the outer AggregateQuery.
              col_cnt = 0
              for alias, expression in list(inner_query.annotation_select.items()):
                  annotation_select_mask = inner_query.annotation_select_mask
                  if expression.is_summary:
                      expression, col_cnt = inner_query.rewrite_cols(expression, col_cnt)
                      outer_query.annotations[alias] = expression.relabeled_clone(relabels)
                      del inner_query.annotations[alias]
                      annotation_select_mask.remove(alias)
                  # Make sure the annotation_select wont use cached results.
                  inner_query.set_annotation_mask(inner_query.annotation_select_mask)
              if inner_query.select == () and not inner_query.default_cols and not inner_query.annotation_select_mask:
                  # In case of Model.objects[0:3].count(), there would be no
                  # field selected in the inner query, yet we must use a subquery.
                  # So, make sure at least one field is selected.
                  inner_query.select = (self.model._meta.pk.get_col(inner_query.get_initial_alias()),)
              try:
                  outer_query.add_subquery(inner_query, using)
              except EmptyResultSet:
                  return {
                      alias: None
                      for alias in outer_query.annotation_select
                  }
          else:
              outer_query = self
              self.select = ()
              self.default_cols = False
              self.extra = {}
  
          outer_query.clear_ordering(True)
          outer_query.clear_limits()
          outer_query.select_for_update = False
          outer_query.select_related = False
          compiler = outer_query.get_compiler(using)
          result = compiler.execute_sql(SINGLE)
          if result is None:
              result = [None] * len(outer_query.annotation_select)
  
          converters = compiler.get_converters(outer_query.annotation_select.values())
          result = next(compiler.apply_converters((result,), converters))
  
          return dict(zip(outer_query.annotation_select, result))
  
      def get_count(self, using):
          """
          Perform a COUNT() query using the current filter constraints.
          """
          obj = self.clone()
          obj.add_annotation(Count('*'), alias='__count', is_summary=True)
          number = obj.get_aggregation(using, ['__count'])['__count']
          if number is None:
              number = 0
          return number
  
      def has_filters(self):
          return self.where
  
      def has_results(self, using):
          q = self.clone()
          if not q.distinct:
              if q.group_by is True:
                  q.add_fields((f.attname for f in self.model._meta.concrete_fields), False)
                  # Disable GROUP BY aliases to avoid orphaning references to the
                  # SELECT clause which is about to be cleared.
                  q.set_group_by(allow_aliases=False)
              q.clear_select_clause()
          q.clear_ordering(True)
          q.set_limits(high=1)
          compiler = q.get_compiler(using=using)
          return compiler.has_results()
  
      def explain(self, using, format=None, **options):
          q = self.clone()
          q.explain_query = True
          q.explain_format = format
          q.explain_options = options
          compiler = q.get_compiler(using=using)
          return '\n'.join(compiler.explain_query())
  
      def combine(self, rhs, connector):
          """
          Merge the 'rhs' query into the current one (with any 'rhs' effects
          being applied *after* (that is, "to the right of") anything in the
          current query. 'rhs' is not modified during a call to this function.
  
          The 'connector' parameter describes how to connect filters from the
          'rhs' query.
          """
          assert self.model == rhs.model, \
              "Cannot combine queries on two different base models."
          assert not self.is_sliced, \
              "Cannot combine queries once a slice has been taken."
          assert self.distinct == rhs.distinct, \
              "Cannot combine a unique query with a non-unique query."
          assert self.distinct_fields == rhs.distinct_fields, \
              "Cannot combine queries with different distinct fields."
  
          # Work out how to relabel the rhs aliases, if necessary.
          change_map = {}
          conjunction = (connector == AND)
  
          # Determine which existing joins can be reused. When combining the
          # query with AND we must recreate all joins for m2m filters. When
          # combining with OR we can reuse joins. The reason is that in AND
          # case a single row can't fulfill a condition like:
          #     revrel__col=1 & revrel__col=2
          # But, there might be two different related rows matching this
          # condition. In OR case a single True is enough, so single row is
          # enough, too.
          #
          # Note that we will be creating duplicate joins for non-m2m joins in
          # the AND case. The results will be correct but this creates too many
          # joins. This is something that could be fixed later on.
          reuse = set() if conjunction else set(self.alias_map)
          # Base table must be present in the query - this is the same
          # table on both sides.
          self.get_initial_alias()
          joinpromoter = JoinPromoter(connector, 2, False)
          joinpromoter.add_votes(
              j for j in self.alias_map if self.alias_map[j].join_type == INNER)
          rhs_votes = set()
          # Now, add the joins from rhs query into the new query (skipping base
          # table).
          rhs_tables = list(rhs.alias_map)[1:]
          for alias in rhs_tables:
              join = rhs.alias_map[alias]
              # If the left side of the join was already relabeled, use the
              # updated alias.
              join = join.relabeled_clone(change_map)
              new_alias = self.join(join, reuse=reuse)
              if join.join_type == INNER:
                  rhs_votes.add(new_alias)
              # We can't reuse the same join again in the query. If we have two
              # distinct joins for the same connection in rhs query, then the
              # combined query must have two joins, too.
              reuse.discard(new_alias)
              if alias != new_alias:
                  change_map[alias] = new_alias
              if not rhs.alias_refcount[alias]:
                  # The alias was unused in the rhs query. Unref it so that it
                  # will be unused in the new query, too. We have to add and
                  # unref the alias so that join promotion has information of
                  # the join type for the unused alias.
                  self.unref_alias(new_alias)
          joinpromoter.add_votes(rhs_votes)
          joinpromoter.update_join_types(self)
  
          # Now relabel a copy of the rhs where-clause and add it to the current
          # one.
          w = rhs.where.clone()
          w.relabel_aliases(change_map)
          self.where.add(w, connector)
  
          # Selection columns and extra extensions are those provided by 'rhs'.
          if rhs.select:
              self.set_select([col.relabeled_clone(change_map) for col in rhs.select])
          else:
              self.select = ()
  
          if connector == OR:
              # It would be nice to be able to handle this, but the queries don't
              # really make sense (or return consistent value sets). Not worth
              # the extra complexity when you can write a real query instead.
              if self.extra and rhs.extra:
                  raise ValueError("When merging querysets using 'or', you cannot have extra(select=...) on both sides.")
          self.extra.update(rhs.extra)
          extra_select_mask = set()
          if self.extra_select_mask is not None:
              extra_select_mask.update(self.extra_select_mask)
          if rhs.extra_select_mask is not None:
              extra_select_mask.update(rhs.extra_select_mask)
          if extra_select_mask:
              self.set_extra_mask(extra_select_mask)
          self.extra_tables += rhs.extra_tables
  
          # Ordering uses the 'rhs' ordering, unless it has none, in which case
          # the current ordering is used.
          self.order_by = rhs.order_by or self.order_by
          self.extra_order_by = rhs.extra_order_by or self.extra_order_by
  
      def deferred_to_data(self, target, callback):
          """
          Convert the self.deferred_loading data structure to an alternate data
          structure, describing the field that *will* be loaded. This is used to
          compute the columns to select from the database and also by the
          QuerySet class to work out which fields are being initialized on each
          model. Models that have all their fields included aren't mentioned in
          the result, only those that have field restrictions in place.
  
          The "target" parameter is the instance that is populated (in place).
          The "callback" is a function that is called whenever a (model, field)
          pair need to be added to "target". It accepts three parameters:
          "target", and the model and list of fields being added for that model.
          """
          field_names, defer = self.deferred_loading
          if not field_names:
              return
          orig_opts = self.get_meta()
          seen = {}
          must_include = {orig_opts.concrete_model: {orig_opts.pk}}
          for field_name in field_names:
              parts = field_name.split(LOOKUP_SEP)
              cur_model = self.model._meta.concrete_model
              opts = orig_opts
              for name in parts[:-1]:
                  old_model = cur_model
                  if name in self._filtered_relations:
                      name = self._filtered_relations[name].relation_name
                  source = opts.get_field(name)
                  if is_reverse_o2o(source):
                      cur_model = source.related_model
                  else:
                      cur_model = source.remote_field.model
                  opts = cur_model._meta
                  # Even if we're "just passing through" this model, we must add
                  # both the current model's pk and the related reference field
                  # (if it's not a reverse relation) to the things we select.
                  if not is_reverse_o2o(source):
                      must_include[old_model].add(source)
                  add_to_dict(must_include, cur_model, opts.pk)
              field = opts.get_field(parts[-1])
              is_reverse_object = field.auto_created and not field.concrete
              model = field.related_model if is_reverse_object else field.model
              model = model._meta.concrete_model
              if model == opts.model:
                  model = cur_model
              if not is_reverse_o2o(field):
                  add_to_dict(seen, model, field)
  
          if defer:
              # We need to load all fields for each model, except those that
              # appear in "seen" (for all models that appear in "seen"). The only
              # slight complexity here is handling fields that exist on parent
              # models.
              workset = {}
              for model, values in seen.items():
                  for field in model._meta.local_fields:
                      if field not in values:
                          m = field.model._meta.concrete_model
                          add_to_dict(workset, m, field)
              for model, values in must_include.items():
                  # If we haven't included a model in workset, we don't add the
                  # corresponding must_include fields for that model, since an
                  # empty set means "include all fields". That's why there's no
                  # "else" branch here.
                  if model in workset:
                      workset[model].update(values)
              for model, values in workset.items():
                  callback(target, model, values)
          else:
              for model, values in must_include.items():
                  if model in seen:
                      seen[model].update(values)
                  else:
                      # As we've passed through this model, but not explicitly
                      # included any fields, we have to make sure it's mentioned
                      # so that only the "must include" fields are pulled in.
                      seen[model] = values
              # Now ensure that every model in the inheritance chain is mentioned
              # in the parent list. Again, it must be mentioned to ensure that
              # only "must include" fields are pulled in.
              for model in orig_opts.get_parent_list():
                  seen.setdefault(model, set())
              for model, values in seen.items():
                  callback(target, model, values)
  
      def table_alias(self, table_name, create=False, filtered_relation=None):
          """
          Return a table alias for the given table_name and whether this is a
          new alias or not.
  
          If 'create' is true, a new alias is always created. Otherwise, the
          most recently created alias for the table (if one exists) is reused.
          """
          alias_list = self.table_map.get(table_name)
          if not create and alias_list:
              alias = alias_list[0]
              self.alias_refcount[alias] += 1
              return alias, False
  
          # Create a new alias for this table.
          if alias_list:
              alias = '%s%d' % (self.alias_prefix, len(self.alias_map) + 1)
              alias_list.append(alias)
          else:
              # The first occurrence of a table uses the table name directly.
              alias = filtered_relation.alias if filtered_relation is not None else table_name
              self.table_map[table_name] = [alias]
          self.alias_refcount[alias] = 1
          return alias, True
  
      def ref_alias(self, alias):
          """Increases the reference count for this alias."""
          self.alias_refcount[alias] += 1
  
      def unref_alias(self, alias, amount=1):
          """Decreases the reference count for this alias."""
          self.alias_refcount[alias] -= amount
  
      def promote_joins(self, aliases):
          """
          Promote recursively the join type of given aliases and its children to
          an outer join. If 'unconditional' is False, only promote the join if
          it is nullable or the parent join is an outer join.
  
          The children promotion is done to avoid join chains that contain a LOUTER
          b INNER c. So, if we have currently a INNER b INNER c and a->b is promoted,
          then we must also promote b->c automatically, or otherwise the promotion
          of a->b doesn't actually change anything in the query results.
          """
          aliases = list(aliases)
          while aliases:
              alias = aliases.pop(0)
              if self.alias_map[alias].join_type is None:
                  # This is the base table (first FROM entry) - this table
                  # isn't really joined at all in the query, so we should not
                  # alter its join type.
                  continue
              # Only the first alias (skipped above) should have None join_type
              assert self.alias_map[alias].join_type is not None
              parent_alias = self.alias_map[alias].parent_alias
              parent_louter = parent_alias and self.alias_map[parent_alias].join_type == LOUTER
              already_louter = self.alias_map[alias].join_type == LOUTER
              if ((self.alias_map[alias].nullable or parent_louter) and
                      not already_louter):
                  self.alias_map[alias] = self.alias_map[alias].promote()
                  # Join type of 'alias' changed, so re-examine all aliases that
                  # refer to this one.
                  aliases.extend(
                      join for join in self.alias_map
                      if self.alias_map[join].parent_alias == alias and join not in aliases
                  )
  
      def demote_joins(self, aliases):
          """
          Change join type from LOUTER to INNER for all joins in aliases.
  
          Similarly to promote_joins(), this method must ensure no join chains
          containing first an outer, then an inner join are generated. If we
          are demoting b->c join in chain a LOUTER b LOUTER c then we must
          demote a->b automatically, or otherwise the demotion of b->c doesn't
          actually change anything in the query results. .
          """
          aliases = list(aliases)
          while aliases:
              alias = aliases.pop(0)
              if self.alias_map[alias].join_type == LOUTER:
                  self.alias_map[alias] = self.alias_map[alias].demote()
                  parent_alias = self.alias_map[alias].parent_alias
                  if self.alias_map[parent_alias].join_type == INNER:
                      aliases.append(parent_alias)
  
      def reset_refcounts(self, to_counts):
          """
          Reset reference counts for aliases so that they match the value passed
          in `to_counts`.
          """
          for alias, cur_refcount in self.alias_refcount.copy().items():
              unref_amount = cur_refcount - to_counts.get(alias, 0)
              self.unref_alias(alias, unref_amount)
  
      def change_aliases(self, change_map):
          """
          Change the aliases in change_map (which maps old-alias -> new-alias),
          relabelling any references to them in select columns and the where
          clause.
          """
          assert set(change_map).isdisjoint(change_map.values())
  
          # 1. Update references in "select" (normal columns plus aliases),
          # "group by" and "where".
          self.where.relabel_aliases(change_map)
          if isinstance(self.group_by, tuple):
              self.group_by = tuple([col.relabeled_clone(change_map) for col in self.group_by])
          self.select = tuple([col.relabeled_clone(change_map) for col in self.select])
          self.annotations = self.annotations and {
              key: col.relabeled_clone(change_map) for key, col in self.annotations.items()
          }
  
          # 2. Rename the alias in the internal table/alias datastructures.
          for old_alias, new_alias in change_map.items():
              if old_alias not in self.alias_map:
                  continue
              alias_data = self.alias_map[old_alias].relabeled_clone(change_map)
              self.alias_map[new_alias] = alias_data
              self.alias_refcount[new_alias] = self.alias_refcount[old_alias]
              del self.alias_refcount[old_alias]
              del self.alias_map[old_alias]
  
              table_aliases = self.table_map[alias_data.table_name]
              for pos, alias in enumerate(table_aliases):
                  if alias == old_alias:
                      table_aliases[pos] = new_alias
                      break
          self.external_aliases = {
              # Table is aliased or it's being changed and thus is aliased.
              change_map.get(alias, alias): (aliased or alias in change_map)
              for alias, aliased in self.external_aliases.items()
          }
  
      def bump_prefix(self, outer_query):
          """
          Change the alias prefix to the next letter in the alphabet in a way
          that the outer query's aliases and this query's aliases will not
          conflict. Even tables that previously had no alias will get an alias
          after this call.
          """
          def prefix_gen():
              """
              Generate a sequence of characters in alphabetical order:
                  -> 'A', 'B', 'C', ...
  
              When the alphabet is finished, the sequence will continue with the
              Cartesian product:
                  -> 'AA', 'AB', 'AC', ...
              """
              alphabet = ascii_uppercase
              prefix = chr(ord(self.alias_prefix) + 1)
              yield prefix
              for n in count(1):
                  seq = alphabet[alphabet.index(prefix):] if prefix else alphabet
                  for s in product(seq, repeat=n):
                      yield ''.join(s)
                  prefix = None
  
          if self.alias_prefix != outer_query.alias_prefix:
              # No clashes between self and outer query should be possible.
              return
  
          # Explicitly avoid infinite loop. The constant divider is based on how
          # much depth recursive subquery references add to the stack. This value
          # might need to be adjusted when adding or removing function calls from
          # the code path in charge of performing these operations.
          local_recursion_limit = sys.getrecursionlimit() // 16
          for pos, prefix in enumerate(prefix_gen()):
              if prefix not in self.subq_aliases:
                  self.alias_prefix = prefix
                  break
              if pos > local_recursion_limit:
                  raise RecursionError(
                      'Maximum recursion depth exceeded: too many subqueries.'
                  )
          self.subq_aliases = self.subq_aliases.union([self.alias_prefix])
          outer_query.subq_aliases = outer_query.subq_aliases.union(self.subq_aliases)
          self.change_aliases({
              alias: '%s%d' % (self.alias_prefix, pos)
              for pos, alias in enumerate(self.alias_map)
          })
  
      def get_initial_alias(self):
          """
          Return the first alias for this query, after increasing its reference
          count.
          """
          if self.alias_map:
              alias = self.base_table
              self.ref_alias(alias)
          else:
              alias = self.join(BaseTable(self.get_meta().db_table, None))
          return alias
  
      def count_active_tables(self):
          """
          Return the number of tables in this query with a non-zero reference
          count. After execution, the reference counts are zeroed, so tables
          added in compiler will not be seen by this method.
          """
          return len([1 for count in self.alias_refcount.values() if count])
  
      def join(self, join, reuse=None, reuse_with_filtered_relation=False):
          """
          Return an alias for the 'join', either reusing an existing alias for
          that join or creating a new one. 'join' is either a
          sql.datastructures.BaseTable or Join.
  
          The 'reuse' parameter can be either None which means all joins are
          reusable, or it can be a set containing the aliases that can be reused.
  
          The 'reuse_with_filtered_relation' parameter is used when computing
          FilteredRelation instances.
  
          A join is always created as LOUTER if the lhs alias is LOUTER to make
          sure chains like t1 LOUTER t2 INNER t3 aren't generated. All new
          joins are created as LOUTER if the join is nullable.
          """
          if reuse_with_filtered_relation and reuse:
              reuse_aliases = [
                  a for a, j in self.alias_map.items()
                  if a in reuse and j.equals(join, with_filtered_relation=False)
              ]
          else:
              reuse_aliases = [
                  a for a, j in self.alias_map.items()
                  if (reuse is None or a in reuse) and j == join
              ]
          if reuse_aliases:
              if join.table_alias in reuse_aliases:
                  reuse_alias = join.table_alias
              else:
                  # Reuse the most recent alias of the joined table
                  # (a many-to-many relation may be joined multiple times).
                  reuse_alias = reuse_aliases[-1]
              self.ref_alias(reuse_alias)
              return reuse_alias
  
          # No reuse is possible, so we need a new alias.
          alias, _ = self.table_alias(join.table_name, create=True, filtered_relation=join.filtered_relation)
          if join.join_type:
              if self.alias_map[join.parent_alias].join_type == LOUTER or join.nullable:
                  join_type = LOUTER
              else:
                  join_type = INNER
              join.join_type = join_type
          join.table_alias = alias
          self.alias_map[alias] = join
          return alias
  
      def join_parent_model(self, opts, model, alias, seen):
          """
          Make sure the given 'model' is joined in the query. If 'model' isn't
          a parent of 'opts' or if it is None this method is a no-op.
  
          The 'alias' is the root alias for starting the join, 'seen' is a dict
          of model -> alias of existing joins. It must also contain a mapping
          of None -> some alias. This will be returned in the no-op case.
          """
          if model in seen:
              return seen[model]
          chain = opts.get_base_chain(model)
          if not chain:
              return alias
          curr_opts = opts
          for int_model in chain:
              if int_model in seen:
                  curr_opts = int_model._meta
                  alias = seen[int_model]
                  continue
              # Proxy model have elements in base chain
              # with no parents, assign the new options
              # object and skip to the next base in that
              # case
              if not curr_opts.parents[int_model]:
                  curr_opts = int_model._meta
                  continue
              link_field = curr_opts.get_ancestor_link(int_model)
              join_info = self.setup_joins([link_field.name], curr_opts, alias)
              curr_opts = int_model._meta
              alias = seen[int_model] = join_info.joins[-1]
          return alias or seen[None]
  
      def add_annotation(self, annotation, alias, is_summary=False):
          """Add a single annotation expression to the Query."""
          annotation = annotation.resolve_expression(self, allow_joins=True, reuse=None,
                                                     summarize=is_summary)
          self.append_annotation_mask([alias])
          self.annotations[alias] = annotation
  
      def resolve_expression(self, query, *args, **kwargs):
          clone = self.clone()
          # Subqueries need to use a different set of aliases than the outer query.
          clone.bump_prefix(query)
          clone.subquery = True
          # It's safe to drop ordering if the queryset isn't using slicing,
          # distinct(*fields) or select_for_update().
          if (self.low_mark == 0 and self.high_mark is None and
                  not self.distinct_fields and
                  not self.select_for_update):
              clone.clear_ordering(True)
          clone.where.resolve_expression(query, *args, **kwargs)
          for key, value in clone.annotations.items():
              resolved = value.resolve_expression(query, *args, **kwargs)
              if hasattr(resolved, 'external_aliases'):
                  resolved.external_aliases.update(clone.external_aliases)
              clone.annotations[key] = resolved
          # Outer query's aliases are considered external.
          for alias, table in query.alias_map.items():
              clone.external_aliases[alias] = (
                  (isinstance(table, Join) and table.join_field.related_model._meta.db_table != alias) or
                  (isinstance(table, BaseTable) and table.table_name != table.table_alias)
              )
          return clone
  
      def get_external_cols(self):
          exprs = chain(self.annotations.values(), self.where.children)
          return [
              col for col in self._gen_cols(exprs)
              if col.alias in self.external_aliases
          ]
  
      def as_sql(self, compiler, connection):
          sql, params = self.get_compiler(connection=connection).as_sql()
          if self.subquery:
              sql = '(%s)' % sql
          return sql, params
  
      def resolve_lookup_value(self, value, can_reuse, allow_joins):
          if hasattr(value, 'resolve_expression'):
              value = value.resolve_expression(
                  self, reuse=can_reuse, allow_joins=allow_joins,
              )
          elif isinstance(value, (list, tuple)):
              # The items of the iterable may be expressions and therefore need
              # to be resolved independently.
              return type(value)(
                  self.resolve_lookup_value(sub_value, can_reuse, allow_joins)
                  for sub_value in value
              )
          return value
  
      def solve_lookup_type(self, lookup):
          """
          Solve the lookup type from the lookup (e.g.: 'foobar__id__icontains').
          """
          lookup_splitted = lookup.split(LOOKUP_SEP)
          if self.annotations:
              expression, expression_lookups = refs_expression(lookup_splitted, self.annotations)
              if expression:
                  return expression_lookups, (), expression
          _, field, _, lookup_parts = self.names_to_path(lookup_splitted, self.get_meta())
          field_parts = lookup_splitted[0:len(lookup_splitted) - len(lookup_parts)]
          if len(lookup_parts) > 1 and not field_parts:
              raise FieldError(
                  'Invalid lookup "%s" for model %s".' %
                  (lookup, self.get_meta().model.__name__)
              )
          return lookup_parts, field_parts, False
  
      def check_query_object_type(self, value, opts, field):
          """
          Check whether the object passed while querying is of the correct type.
          If not, raise a ValueError specifying the wrong object.
          """
          if hasattr(value, '_meta'):
              if not check_rel_lookup_compatibility(value._meta.model, opts, field):
                  raise ValueError(
                      'Cannot query "%s": Must be "%s" instance.' %
                      (value, opts.object_name))
  
      def check_related_objects(self, field, value, opts):
          """Check the type of object passed to query relations."""
          if field.is_relation:
              # Check that the field and the queryset use the same model in a
              # query like .filter(author=Author.objects.all()). For example, the
              # opts would be Author's (from the author field) and value.model
              # would be Author.objects.all() queryset's .model (Author also).
              # The field is the related field on the lhs side.
              if (isinstance(value, Query) and not value.has_select_fields and
                      not check_rel_lookup_compatibility(value.model, opts, field)):
                  raise ValueError(
                      'Cannot use QuerySet for "%s": Use a QuerySet for "%s".' %
                      (value.model._meta.object_name, opts.object_name)
                  )
              elif hasattr(value, '_meta'):
                  self.check_query_object_type(value, opts, field)
              elif hasattr(value, '__iter__'):
                  for v in value:
                      self.check_query_object_type(v, opts, field)
  
      def check_filterable(self, expression):
          """Raise an error if expression cannot be used in a WHERE clause."""
          if not getattr(expression, 'filterable', True):
              raise NotSupportedError(
                  expression.__class__.__name__ + ' is disallowed in the filter '
                  'clause.'
              )
          if hasattr(expression, 'get_source_expressions'):
              for expr in expression.get_source_expressions():
                  self.check_filterable(expr)
  
      def build_lookup(self, lookups, lhs, rhs):
          """
          Try to extract transforms and lookup from given lhs.
  
          The lhs value is something that works like SQLExpression.
          The rhs value is what the lookup is going to compare against.
          The lookups is a list of names to extract using get_lookup()
          and get_transform().
          """
          # __exact is the default lookup if one isn't given.
          *transforms, lookup_name = lookups or ['exact']
          for name in transforms:
              lhs = self.try_transform(lhs, name)
          # First try get_lookup() so that the lookup takes precedence if the lhs
          # supports both transform and lookup for the name.
          lookup_class = lhs.get_lookup(lookup_name)
          if not lookup_class:
              if lhs.field.is_relation:
                  raise FieldError('Related Field got invalid lookup: {}'.format(lookup_name))
              # A lookup wasn't found. Try to interpret the name as a transform
              # and do an Exact lookup against it.
              lhs = self.try_transform(lhs, lookup_name)
              lookup_name = 'exact'
              lookup_class = lhs.get_lookup(lookup_name)
              if not lookup_class:
                  return
  
          lookup = lookup_class(lhs, rhs)
          # Interpret '__exact=None' as the sql 'is NULL'; otherwise, reject all
          # uses of None as a query value unless the lookup supports it.
          if lookup.rhs is None and not lookup.can_use_none_as_rhs:
              if lookup_name not in ('exact', 'iexact'):
                  raise ValueError("Cannot use None as a query value")
              return lhs.get_lookup('isnull')(lhs, True)
  
          # For Oracle '' is equivalent to null. The check must be done at this
          # stage because join promotion can't be done in the compiler. Using
          # DEFAULT_DB_ALIAS isn't nice but it's the best that can be done here.
          # A similar thing is done in is_nullable(), too.
          if (connections[DEFAULT_DB_ALIAS].features.interprets_empty_strings_as_nulls and
                  lookup_name == 'exact' and lookup.rhs == ''):
              return lhs.get_lookup('isnull')(lhs, True)
  
          return lookup
  
      def try_transform(self, lhs, name):
          """
          Helper method for build_lookup(). Try to fetch and initialize
          a transform for name parameter from lhs.
          """
          transform_class = lhs.get_transform(name)
          if transform_class:
              return transform_class(lhs)
          else:
              output_field = lhs.output_field.__class__
              suggested_lookups = difflib.get_close_matches(name, output_field.get_lookups())
              if suggested_lookups:
                  suggestion = ', perhaps you meant %s?' % ' or '.join(suggested_lookups)
              else:
                  suggestion = '.'
              raise FieldError(
                  "Unsupported lookup '%s' for %s or join on the field not "
                  "permitted%s" % (name, output_field.__name__, suggestion)
              )
  
      def build_filter(self, filter_expr, branch_negated=False, current_negated=False,
                       can_reuse=None, allow_joins=True, split_subq=True,
                       reuse_with_filtered_relation=False, check_filterable=True):
          """
          Build a WhereNode for a single filter clause but don't add it
          to this Query. Query.add_q() will then add this filter to the where
          Node.
  
          The 'branch_negated' tells us if the current branch contains any
          negations. This will be used to determine if subqueries are needed.
  
          The 'current_negated' is used to determine if the current filter is
          negated or not and this will be used to determine if IS NULL filtering
          is needed.
  
          The difference between current_negated and branch_negated is that
          branch_negated is set on first negation, but current_negated is
          flipped for each negation.
  
          Note that add_filter will not do any negating itself, that is done
          upper in the code by add_q().
  
          The 'can_reuse' is a set of reusable joins for multijoins.
  
          If 'reuse_with_filtered_relation' is True, then only joins in can_reuse
          will be reused.
  
          The method will create a filter clause that can be added to the current
          query. However, if the filter isn't added to the query then the caller
          is responsible for unreffing the joins used.
          """
          if isinstance(filter_expr, dict):
              raise FieldError("Cannot parse keyword query as dict")
          if isinstance(filter_expr, Q):
              return self._add_q(
                  filter_expr,
                  branch_negated=branch_negated,
                  current_negated=current_negated,
                  used_aliases=can_reuse,
                  allow_joins=allow_joins,
                  split_subq=split_subq,
                  check_filterable=check_filterable,
              )
          if hasattr(filter_expr, 'resolve_expression'):
              if not getattr(filter_expr, 'conditional', False):
                  raise TypeError('Cannot filter against a non-conditional expression.')
              condition = self.build_lookup(
                  ['exact'], filter_expr.resolve_expression(self, allow_joins=allow_joins), True
              )
              clause = self.where_class()
              clause.add(condition, AND)
              return clause, []
          arg, value = filter_expr
          if not arg:
              raise FieldError("Cannot parse keyword query %r" % arg)
          lookups, parts, reffed_expression = self.solve_lookup_type(arg)
  
          if check_filterable:
              self.check_filterable(reffed_expression)
  
          if not allow_joins and len(parts) > 1:
              raise FieldError("Joined field references are not permitted in this query")
  
          pre_joins = self.alias_refcount.copy()
          value = self.resolve_lookup_value(value, can_reuse, allow_joins)
          used_joins = {k for k, v in self.alias_refcount.items() if v > pre_joins.get(k, 0)}
  
          if check_filterable:
              self.check_filterable(value)
  
          clause = self.where_class()
          if reffed_expression:
              condition = self.build_lookup(lookups, reffed_expression, value)
              clause.add(condition, AND)
              return clause, []
  
          opts = self.get_meta()
          alias = self.get_initial_alias()
          allow_many = not branch_negated or not split_subq
  
          try:
              join_info = self.setup_joins(
                  parts, opts, alias, can_reuse=can_reuse, allow_many=allow_many,
                  reuse_with_filtered_relation=reuse_with_filtered_relation,
              )
  
              # Prevent iterator from being consumed by check_related_objects()
              if isinstance(value, Iterator):
                  value = list(value)
              self.check_related_objects(join_info.final_field, value, join_info.opts)
  
              # split_exclude() needs to know which joins were generated for the
              # lookup parts
              self._lookup_joins = join_info.joins
          except MultiJoin as e:
              return self.split_exclude(filter_expr, can_reuse, e.names_with_path)
  
          # Update used_joins before trimming since they are reused to determine
          # which joins could be later promoted to INNER.
          used_joins.update(join_info.joins)
          targets, alias, join_list = self.trim_joins(join_info.targets, join_info.joins, join_info.path)
          if can_reuse is not None:
              can_reuse.update(join_list)
  
          if join_info.final_field.is_relation:
              # No support for transforms for relational fields
              num_lookups = len(lookups)
              if num_lookups > 1:
                  raise FieldError('Related Field got invalid lookup: {}'.format(lookups[0]))
              if len(targets) == 1:
                  col = self._get_col(targets[0], join_info.final_field, alias)
              else:
                  col = MultiColSource(alias, targets, join_info.targets, join_info.final_field)
          else:
              col = self._get_col(targets[0], join_info.final_field, alias)
  
          condition = self.build_lookup(lookups, col, value)
          lookup_type = condition.lookup_name
          clause.add(condition, AND)
  
          require_outer = lookup_type == 'isnull' and condition.rhs is True and not current_negated
          if current_negated and (lookup_type != 'isnull' or condition.rhs is False) and condition.rhs is not None:
              require_outer = True
              if (lookup_type != 'isnull' and (
                      self.is_nullable(targets[0]) or
                      self.alias_map[join_list[-1]].join_type == LOUTER)):
                  # The condition added here will be SQL like this:
                  # NOT (col IS NOT NULL), where the first NOT is added in
                  # upper layers of code. The reason for addition is that if col
                  # is null, then col != someval will result in SQL "unknown"
                  # which isn't the same as in Python. The Python None handling
                  # is wanted, and it can be gotten by
                  # (col IS NULL OR col != someval)
                  #   <=>
                  # NOT (col IS NOT NULL AND col = someval).
                  lookup_class = targets[0].get_lookup('isnull')
                  col = self._get_col(targets[0], join_info.targets[0], alias)
                  clause.add(lookup_class(col, False), AND)
          return clause, used_joins if not require_outer else ()
  
      def add_filter(self, filter_clause):
          self.add_q(Q(**{filter_clause[0]: filter_clause[1]}))
  
      def add_q(self, q_object):
          """
          A preprocessor for the internal _add_q(). Responsible for doing final
          join promotion.
          """
          # For join promotion this case is doing an AND for the added q_object
          # and existing conditions. So, any existing inner join forces the join
          # type to remain inner. Existing outer joins can however be demoted.
          # (Consider case where rel_a is LOUTER and rel_a__col=1 is added - if
          # rel_a doesn't produce any rows, then the whole condition must fail.
          # So, demotion is OK.
          existing_inner = {a for a in self.alias_map if self.alias_map[a].join_type == INNER}
          clause, _ = self._add_q(q_object, self.used_aliases)
          if clause:
              self.where.add(clause, AND)
          self.demote_joins(existing_inner)
  
      def build_where(self, filter_expr):
          return self.build_filter(filter_expr, allow_joins=False)[0]
  
      def _add_q(self, q_object, used_aliases, branch_negated=False,
                 current_negated=False, allow_joins=True, split_subq=True,
                 check_filterable=True):
          """Add a Q-object to the current filter."""
          connector = q_object.connector
          current_negated = current_negated ^ q_object.negated
          branch_negated = branch_negated or q_object.negated
          target_clause = self.where_class(connector=connector,
                                           negated=q_object.negated)
          joinpromoter = JoinPromoter(q_object.connector, len(q_object.children), current_negated)
          for child in q_object.children:
              child_clause, needed_inner = self.build_filter(
                  child, can_reuse=used_aliases, branch_negated=branch_negated,
                  current_negated=current_negated, allow_joins=allow_joins,
                  split_subq=split_subq, check_filterable=check_filterable,
              )
              joinpromoter.add_votes(needed_inner)
              if child_clause:
                  target_clause.add(child_clause, connector)
          needed_inner = joinpromoter.update_join_types(self)
          return target_clause, needed_inner
  
      def build_filtered_relation_q(self, q_object, reuse, branch_negated=False, current_negated=False):
          """Add a FilteredRelation object to the current filter."""
          connector = q_object.connector
          current_negated ^= q_object.negated
          branch_negated = branch_negated or q_object.negated
          target_clause = self.where_class(connector=connector, negated=q_object.negated)
          for child in q_object.children:
              if isinstance(child, Node):
                  child_clause = self.build_filtered_relation_q(
                      child, reuse=reuse, branch_negated=branch_negated,
                      current_negated=current_negated,
                  )
              else:
                  child_clause, _ = self.build_filter(
                      child, can_reuse=reuse, branch_negated=branch_negated,
                      current_negated=current_negated,
                      allow_joins=True, split_subq=False,
                      reuse_with_filtered_relation=True,
                  )
              target_clause.add(child_clause, connector)
          return target_clause
  
      def add_filtered_relation(self, filtered_relation, alias):
          filtered_relation.alias = alias
          lookups = dict(get_children_from_q(filtered_relation.condition))
          for lookup in chain((filtered_relation.relation_name,), lookups):
              lookup_parts, field_parts, _ = self.solve_lookup_type(lookup)
              shift = 2 if not lookup_parts else 1
              if len(field_parts) > (shift + len(lookup_parts)):
                  raise ValueError(
                      "FilteredRelation's condition doesn't support nested "
                      "relations (got %r)." % lookup
                  )
          self._filtered_relations[filtered_relation.alias] = filtered_relation
  
      def names_to_path(self, names, opts, allow_many=True, fail_on_missing=False):
          """
          Walk the list of names and turns them into PathInfo tuples. A single
          name in 'names' can generate multiple PathInfos (m2m, for example).
  
          'names' is the path of names to travel, 'opts' is the model Options we
          start the name resolving from, 'allow_many' is as for setup_joins().
          If fail_on_missing is set to True, then a name that can't be resolved
          will generate a FieldError.
  
          Return a list of PathInfo tuples. In addition return the final field
          (the last used join field) and target (which is a field guaranteed to
          contain the same value as the final field). Finally, return those names
          that weren't found (which are likely transforms and the final lookup).
          """
          path, names_with_path = [], []
          for pos, name in enumerate(names):
              cur_names_with_path = (name, [])
              if name == 'pk':
                  name = opts.pk.name
  
              field = None
              filtered_relation = None
              try:
                  field = opts.get_field(name)
              except FieldDoesNotExist:
                  if name in self.annotation_select:
                      field = self.annotation_select[name].output_field
                  elif name in self._filtered_relations and pos == 0:
                      filtered_relation = self._filtered_relations[name]
                      field = opts.get_field(filtered_relation.relation_name)
              if field is not None:
                  # Fields that contain one-to-many relations with a generic
                  # model (like a GenericForeignKey) cannot generate reverse
                  # relations and therefore cannot be used for reverse querying.
                  if field.is_relation and not field.related_model:
                      raise FieldError(
                          "Field %r does not generate an automatic reverse "
                          "relation and therefore cannot be used for reverse "
                          "querying. If it is a GenericForeignKey, consider "
                          "adding a GenericRelation." % name
                      )
                  try:
                      model = field.model._meta.concrete_model
                  except AttributeError:
                      # QuerySet.annotate() may introduce fields that aren't
                      # attached to a model.
                      model = None
              else:
                  # We didn't find the current field, so move position back
                  # one step.
                  pos -= 1
                  if pos == -1 or fail_on_missing:
                      available = sorted([
                          *get_field_names_from_opts(opts),
                          *self.annotation_select,
                          *self._filtered_relations,
                      ])
                      raise FieldError("Cannot resolve keyword '%s' into field. "
                                       "Choices are: %s" % (name, ", ".join(available)))
                  break
              # Check if we need any joins for concrete inheritance cases (the
              # field lives in parent, but we are currently in one of its
              # children)
              if model is not opts.model:
                  path_to_parent = opts.get_path_to_parent(model)
                  if path_to_parent:
                      path.extend(path_to_parent)
                      cur_names_with_path[1].extend(path_to_parent)
                      opts = path_to_parent[-1].to_opts
              if hasattr(field, 'get_path_info'):
                  pathinfos = field.get_path_info(filtered_relation)
                  if not allow_many:
                      for inner_pos, p in enumerate(pathinfos):
                          if p.m2m:
                              cur_names_with_path[1].extend(pathinfos[0:inner_pos + 1])
                              names_with_path.append(cur_names_with_path)
                              raise MultiJoin(pos + 1, names_with_path)
                  last = pathinfos[-1]
                  path.extend(pathinfos)
                  final_field = last.join_field
                  opts = last.to_opts
                  targets = last.target_fields
                  cur_names_with_path[1].extend(pathinfos)
                  names_with_path.append(cur_names_with_path)
              else:
                  # Local non-relational field.
                  final_field = field
                  targets = (field,)
                  if fail_on_missing and pos + 1 != len(names):
                      raise FieldError(
                          "Cannot resolve keyword %r into field. Join on '%s'"
                          " not permitted." % (names[pos + 1], name))
                  break
          return path, final_field, targets, names[pos + 1:]
  
      def setup_joins(self, names, opts, alias, can_reuse=None, allow_many=True,
                      reuse_with_filtered_relation=False):
          """
          Compute the necessary table joins for the passage through the fields
          given in 'names'. 'opts' is the Options class for the current model
          (which gives the table we are starting from), 'alias' is the alias for
          the table to start the joining from.
  
          The 'can_reuse' defines the reverse foreign key joins we can reuse. It
          can be None in which case all joins are reusable or a set of aliases
          that can be reused. Note that non-reverse foreign keys are always
          reusable when using setup_joins().
  
          The 'reuse_with_filtered_relation' can be used to force 'can_reuse'
          parameter and force the relation on the given connections.
  
          If 'allow_many' is False, then any reverse foreign key seen will
          generate a MultiJoin exception.
  
          Return the final field involved in the joins, the target field (used
          for any 'where' constraint), the final 'opts' value, the joins, the
          field path traveled to generate the joins, and a transform function
          that takes a field and alias and is equivalent to `field.get_col(alias)`
          in the simple case but wraps field transforms if they were included in
          names.
  
          The target field is the field containing the concrete value. Final
          field can be something different, for example foreign key pointing to
          that value. Final field is needed for example in some value
          conversions (convert 'obj' in fk__id=obj to pk val using the foreign
          key field for example).
          """
          joins = [alias]
          # The transform can't be applied yet, as joins must be trimmed later.
          # To avoid making every caller of this method look up transforms
          # directly, compute transforms here and create a partial that converts
          # fields to the appropriate wrapped version.
  
          def final_transformer(field, alias):
              return field.get_col(alias)
  
          # Try resolving all the names as fields first. If there's an error,
          # treat trailing names as lookups until a field can be resolved.
          last_field_exception = None
          for pivot in range(len(names), 0, -1):
              try:
                  path, final_field, targets, rest = self.names_to_path(
                      names[:pivot], opts, allow_many, fail_on_missing=True,
                  )
              except FieldError as exc:
                  if pivot == 1:
                      # The first item cannot be a lookup, so it's safe
                      # to raise the field error here.
                      raise
                  else:
                      last_field_exception = exc
              else:
                  # The transforms are the remaining items that couldn't be
                  # resolved into fields.
                  transforms = names[pivot:]
                  break
          for name in transforms:
              def transform(field, alias, *, name, previous):
                  try:
                      wrapped = previous(field, alias)
                      return self.try_transform(wrapped, name)
                  except FieldError:
                      # FieldError is raised if the transform doesn't exist.
                      if isinstance(final_field, Field) and last_field_exception:
                          raise last_field_exception
                      else:
                          raise
              final_transformer = functools.partial(transform, name=name, previous=final_transformer)
          # Then, add the path to the query's joins. Note that we can't trim
          # joins at this stage - we will need the information about join type
          # of the trimmed joins.
          for join in path:
              if join.filtered_relation:
                  filtered_relation = join.filtered_relation.clone()
                  table_alias = filtered_relation.alias
              else:
                  filtered_relation = None
                  table_alias = None
              opts = join.to_opts
              if join.direct:
                  nullable = self.is_nullable(join.join_field)
              else:
                  nullable = True
              connection = Join(
                  opts.db_table, alias, table_alias, INNER, join.join_field,
                  nullable, filtered_relation=filtered_relation,
              )
              reuse = can_reuse if join.m2m or reuse_with_filtered_relation else None
              alias = self.join(
                  connection, reuse=reuse,
                  reuse_with_filtered_relation=reuse_with_filtered_relation,
              )
              joins.append(alias)
              if filtered_relation:
                  filtered_relation.path = joins[:]
          return JoinInfo(final_field, targets, opts, joins, path, final_transformer)
  
      def trim_joins(self, targets, joins, path):
          """
          The 'target' parameter is the final field being joined to, 'joins'
          is the full list of join aliases. The 'path' contain the PathInfos
          used to create the joins.
  
          Return the final target field and table alias and the new active
          joins.
  
          Always trim any direct join if the target column is already in the
          previous table. Can't trim reverse joins as it's unknown if there's
          anything on the other side of the join.
          """
          joins = joins[:]
          for pos, info in enumerate(reversed(path)):
              if len(joins) == 1 or not info.direct:
                  break
              if info.filtered_relation:
                  break
              join_targets = {t.column for t in info.join_field.foreign_related_fields}
              cur_targets = {t.column for t in targets}
              if not cur_targets.issubset(join_targets):
                  break
              targets_dict = {r[1].column: r[0] for r in info.join_field.related_fields if r[1].column in cur_targets}
              targets = tuple(targets_dict[t.column] for t in targets)
              self.unref_alias(joins.pop())
          return targets, joins[-1], joins
  
      @classmethod
      def _gen_cols(cls, exprs):
          for expr in exprs:
              if isinstance(expr, Col):
                  yield expr
              else:
                  yield from cls._gen_cols(expr.get_source_expressions())
  
      @classmethod
      def _gen_col_aliases(cls, exprs):
          yield from (expr.alias for expr in cls._gen_cols(exprs))
  
      def resolve_ref(self, name, allow_joins=True, reuse=None, summarize=False):
          if not allow_joins and LOOKUP_SEP in name:
              raise FieldError("Joined field references are not permitted in this query")
          annotation = self.annotations.get(name)
          if annotation is not None:
              if not allow_joins:
                  for alias in self._gen_col_aliases([annotation]):
                      if isinstance(self.alias_map[alias], Join):
                          raise FieldError(
                              'Joined field references are not permitted in '
                              'this query'
                          )
              if summarize:
                  # Summarize currently means we are doing an aggregate() query
                  # which is executed as a wrapped subquery if any of the
                  # aggregate() elements reference an existing annotation. In
                  # that case we need to return a Ref to the subquery's annotation.
                  return Ref(name, self.annotation_select[name])
              else:
                  return annotation
          else:
              field_list = name.split(LOOKUP_SEP)
              join_info = self.setup_joins(field_list, self.get_meta(), self.get_initial_alias(), can_reuse=reuse)
              targets, final_alias, join_list = self.trim_joins(join_info.targets, join_info.joins, join_info.path)
              if not allow_joins and len(join_list) > 1:
                  raise FieldError('Joined field references are not permitted in this query')
              if len(targets) > 1:
                  raise FieldError("Referencing multicolumn fields with F() objects "
                                   "isn't supported")
              # Verify that the last lookup in name is a field or a transform:
              # transform_function() raises FieldError if not.
              join_info.transform_function(targets[0], final_alias)
              if reuse is not None:
                  reuse.update(join_list)
              return self._get_col(targets[0], join_info.targets[0], join_list[-1])
  
      def split_exclude(self, filter_expr, can_reuse, names_with_path):
          """
          When doing an exclude against any kind of N-to-many relation, we need
          to use a subquery. This method constructs the nested query, given the
          original exclude filter (filter_expr) and the portion up to the first
          N-to-many relation field.
  
          For example, if the origin filter is ~Q(child__name='foo'), filter_expr
          is ('child__name', 'foo') and can_reuse is a set of joins usable for
          filters in the original query.
  
          We will turn this into equivalent of:
              WHERE NOT (pk IN (SELECT parent_id FROM thetable
                                WHERE name = 'foo' AND parent_id IS NOT NULL))
  
          It might be worth it to consider using WHERE NOT EXISTS as that has
          saner null handling, and is easier for the backend's optimizer to
          handle.
          """
          filter_lhs, filter_rhs = filter_expr
          if isinstance(filter_rhs, OuterRef):
              filter_expr = (filter_lhs, OuterRef(filter_rhs))
          elif isinstance(filter_rhs, F):
              filter_expr = (filter_lhs, OuterRef(filter_rhs.name))
          # Generate the inner query.
          query = Query(self.model)
          query._filtered_relations = self._filtered_relations
          query.add_filter(filter_expr)
          query.clear_ordering(True)
          # Try to have as simple as possible subquery -> trim leading joins from
          # the subquery.
          trimmed_prefix, contains_louter = query.trim_start(names_with_path)
  
          # Add extra check to make sure the selected field will not be null
          # since we are adding an IN <subquery> clause. This prevents the
          # database from tripping over IN (...,NULL,...) selects and returning
          # nothing
          col = query.select[0]
          select_field = col.target
          alias = col.alias
          if self.is_nullable(select_field):
              lookup_class = select_field.get_lookup('isnull')
              lookup = lookup_class(select_field.get_col(alias), False)
              query.where.add(lookup, AND)
          if alias in can_reuse:
              pk = select_field.model._meta.pk
              # Need to add a restriction so that outer query's filters are in effect for
              # the subquery, too.
              query.bump_prefix(self)
              lookup_class = select_field.get_lookup('exact')
              # Note that the query.select[0].alias is different from alias
              # due to bump_prefix above.
              lookup = lookup_class(pk.get_col(query.select[0].alias),
                                    pk.get_col(alias))
              query.where.add(lookup, AND)
              query.external_aliases[alias] = True
  
          condition, needed_inner = self.build_filter(
              ('%s__in' % trimmed_prefix, query),
              current_negated=True, branch_negated=True, can_reuse=can_reuse)
          if contains_louter:
              or_null_condition, _ = self.build_filter(
                  ('%s__isnull' % trimmed_prefix, True),
                  current_negated=True, branch_negated=True, can_reuse=can_reuse)
              condition.add(or_null_condition, OR)
              # Note that the end result will be:
              # (outercol NOT IN innerq AND outercol IS NOT NULL) OR outercol IS NULL.
              # This might look crazy but due to how IN works, this seems to be
              # correct. If the IS NOT NULL check is removed then outercol NOT
              # IN will return UNKNOWN. If the IS NULL check is removed, then if
              # outercol IS NULL we will not match the row.
          return condition, needed_inner
  
      def set_empty(self):
          self.where.add(NothingNode(), AND)
  
      def is_empty(self):
          return any(isinstance(c, NothingNode) for c in self.where.children)
  
      def set_limits(self, low=None, high=None):
          """
          Adjust the limits on the rows retrieved. Use low/high to set these,
          as it makes it more Pythonic to read and write. When the SQL query is
          created, convert them to the appropriate offset and limit values.
  
          Apply any limits passed in here to the existing constraints. Add low
          to the current low value and clamp both to any existing high value.
          """
          if high is not None:
              if self.high_mark is not None:
                  self.high_mark = min(self.high_mark, self.low_mark + high)
              else:
                  self.high_mark = self.low_mark + high
          if low is not None:
              if self.high_mark is not None:
                  self.low_mark = min(self.high_mark, self.low_mark + low)
              else:
                  self.low_mark = self.low_mark + low
  
          if self.low_mark == self.high_mark:
              self.set_empty()
  
      def clear_limits(self):
          """Clear any existing limits."""
          self.low_mark, self.high_mark = 0, None
  
      @property
      def is_sliced(self):
          return self.low_mark != 0 or self.high_mark is not None
  
      def has_limit_one(self):
          return self.high_mark is not None and (self.high_mark - self.low_mark) == 1
  
      def can_filter(self):
          """
          Return True if adding filters to this instance is still possible.
  
          Typically, this means no limits or offsets have been put on the results.
          """
          return not self.is_sliced
  
      def clear_select_clause(self):
          """Remove all fields from SELECT clause."""
          self.select = ()
          self.default_cols = False
          self.select_related = False
          self.set_extra_mask(())
          self.set_annotation_mask(())
  
      def clear_select_fields(self):
          """
          Clear the list of fields to select (but not extra_select columns).
          Some queryset types completely replace any existing list of select
          columns.
          """
          self.select = ()
          self.values_select = ()
  
      def add_select_col(self, col):
          self.select += col,
          self.values_select += col.output_field.name,
  
      def set_select(self, cols):
          self.default_cols = False
          self.select = tuple(cols)
  
      def add_distinct_fields(self, *field_names):
          """
          Add and resolve the given fields to the query's "distinct on" clause.
          """
          self.distinct_fields = field_names
          self.distinct = True
  
      def add_fields(self, field_names, allow_m2m=True):
          """
          Add the given (model) fields to the select set. Add the field names in
          the order specified.
          """
          alias = self.get_initial_alias()
          opts = self.get_meta()
  
          try:
              cols = []
              for name in field_names:
                  # Join promotion note - we must not remove any rows here, so
                  # if there is no existing joins, use outer join.
                  join_info = self.setup_joins(name.split(LOOKUP_SEP), opts, alias, allow_many=allow_m2m)
                  targets, final_alias, joins = self.trim_joins(
                      join_info.targets,
                      join_info.joins,
                      join_info.path,
                  )
                  for target in targets:
                      cols.append(join_info.transform_function(target, final_alias))
              if cols:
                  self.set_select(cols)
          except MultiJoin:
              raise FieldError("Invalid field name: '%s'" % name)
          except FieldError:
              if LOOKUP_SEP in name:
                  # For lookups spanning over relationships, show the error
                  # from the model on which the lookup failed.
                  raise
              else:
                  names = sorted([
                      *get_field_names_from_opts(opts), *self.extra,
                      *self.annotation_select, *self._filtered_relations
                  ])
                  raise FieldError("Cannot resolve keyword %r into field. "
                                   "Choices are: %s" % (name, ", ".join(names)))
  
      def add_ordering(self, *ordering):
          """
          Add items from the 'ordering' sequence to the query's "order by"
          clause. These items are either field names (not column names) --
          possibly with a direction prefix ('-' or '?') -- or OrderBy
          expressions.
  
          If 'ordering' is empty, clear all ordering from the query.
          """
          errors = []
          for item in ordering:
              if isinstance(item, str):
                  if '.' in item:
                      warnings.warn(
                          'Passing column raw column aliases to order_by() is '
                          'deprecated. Wrap %r in a RawSQL expression before '
                          'passing it to order_by().' % item,
                          category=RemovedInDjango40Warning,
                          stacklevel=3,
                      )
                      continue
                  if item == '?':
                      continue
                  if item.startswith('-'):
                      item = item[1:]
                  if item in self.annotations:
                      continue
                  if self.extra and item in self.extra:
                      continue
                  # names_to_path() validates the lookup. A descriptive
                  # FieldError will be raise if it's not.
                  self.names_to_path(item.split(LOOKUP_SEP), self.model._meta)
              elif not hasattr(item, 'resolve_expression'):
                  errors.append(item)
              if getattr(item, 'contains_aggregate', False):
                  raise FieldError(
                      'Using an aggregate in order_by() without also including '
                      'it in annotate() is not allowed: %s' % item
                  )
          if errors:
              raise FieldError('Invalid order_by arguments: %s' % errors)
          if ordering:
              self.order_by += ordering
          else:
              self.default_ordering = False
  
      def clear_ordering(self, force_empty):
          """
          Remove any ordering settings. If 'force_empty' is True, there will be
          no ordering in the resulting query (not even the model's default).
          """
          self.order_by = ()
          self.extra_order_by = ()
          if force_empty:
              self.default_ordering = False
  
      def set_group_by(self, allow_aliases=True):
          """
          Expand the GROUP BY clause required by the query.
  
          This will usually be the set of all non-aggregate fields in the
          return data. If the database backend supports grouping by the
          primary key, and the query would be equivalent, the optimization
          will be made automatically.
          """
          # Column names from JOINs to check collisions with aliases.
          if allow_aliases:
              column_names = set()
              seen_models = set()
              for join in list(self.alias_map.values())[1:]:  # Skip base table.
                  model = join.join_field.related_model
                  if model not in seen_models:
                      column_names.update({
                          field.column
                          for field in model._meta.local_concrete_fields
                      })
                      seen_models.add(model)
  
          group_by = list(self.select)
          if self.annotation_select:
              for alias, annotation in self.annotation_select.items():
                  signature = inspect.signature(annotation.get_group_by_cols)
                  if 'alias' not in signature.parameters:
                      annotation_class = annotation.__class__
                      msg = (
                          '`alias=None` must be added to the signature of '
                          '%s.%s.get_group_by_cols().'
                      ) % (annotation_class.__module__, annotation_class.__qualname__)
                      warnings.warn(msg, category=RemovedInDjango40Warning)
                      group_by_cols = annotation.get_group_by_cols()
                  else:
                      if not allow_aliases or alias in column_names:
                          alias = None
                      group_by_cols = annotation.get_group_by_cols(alias=alias)
                  group_by.extend(group_by_cols)
          self.group_by = tuple(group_by)
  
      def add_select_related(self, fields):
          """
          Set up the select_related data structure so that we only select
          certain related models (as opposed to all models, when
          self.select_related=True).
          """
          if isinstance(self.select_related, bool):
              field_dict = {}
          else:
              field_dict = self.select_related
          for field in fields:
              d = field_dict
              for part in field.split(LOOKUP_SEP):
                  d = d.setdefault(part, {})
          self.select_related = field_dict
  
      def add_extra(self, select, select_params, where, params, tables, order_by):
          """
          Add data to the various extra_* attributes for user-created additions
          to the query.
          """
          if select:
              # We need to pair any placeholder markers in the 'select'
              # dictionary with their parameters in 'select_params' so that
              # subsequent updates to the select dictionary also adjust the
              # parameters appropriately.
              select_pairs = {}
              if select_params:
                  param_iter = iter(select_params)
              else:
                  param_iter = iter([])
              for name, entry in select.items():
                  entry = str(entry)
                  entry_params = []
                  pos = entry.find("%s")
                  while pos != -1:
                      if pos == 0 or entry[pos - 1] != '%':
                          entry_params.append(next(param_iter))
                      pos = entry.find("%s", pos + 2)
                  select_pairs[name] = (entry, entry_params)
              self.extra.update(select_pairs)
          if where or params:
              self.where.add(ExtraWhere(where, params), AND)
          if tables:
              self.extra_tables += tuple(tables)
          if order_by:
              self.extra_order_by = order_by
  
      def clear_deferred_loading(self):
          """Remove any fields from the deferred loading set."""
          self.deferred_loading = (frozenset(), True)
  
      def add_deferred_loading(self, field_names):
          """
          Add the given list of model field names to the set of fields to
          exclude from loading from the database when automatic column selection
          is done. Add the new field names to any existing field names that
          are deferred (or removed from any existing field names that are marked
          as the only ones for immediate loading).
          """
          # Fields on related models are stored in the literal double-underscore
          # format, so that we can use a set datastructure. We do the foo__bar
          # splitting and handling when computing the SQL column names (as part of
          # get_columns()).
          existing, defer = self.deferred_loading
          if defer:
              # Add to existing deferred names.
              self.deferred_loading = existing.union(field_names), True
          else:
              # Remove names from the set of any existing "immediate load" names.
              self.deferred_loading = existing.difference(field_names), False
  
      def add_immediate_loading(self, field_names):
          """
          Add the given list of model field names to the set of fields to
          retrieve when the SQL is executed ("immediate loading" fields). The
          field names replace any existing immediate loading field names. If
          there are field names already specified for deferred loading, remove
          those names from the new field_names before storing the new names
          for immediate loading. (That is, immediate loading overrides any
          existing immediate values, but respects existing deferrals.)
          """
          existing, defer = self.deferred_loading
          field_names = set(field_names)
          if 'pk' in field_names:
              field_names.remove('pk')
              field_names.add(self.get_meta().pk.name)
  
          if defer:
              # Remove any existing deferred names from the current set before
              # setting the new names.
              self.deferred_loading = field_names.difference(existing), False
          else:
              # Replace any existing "immediate load" field names.
              self.deferred_loading = frozenset(field_names), False
  
      def get_loaded_field_names(self):
          """
          If any fields are marked to be deferred, return a dictionary mapping
          models to a set of names in those fields that will be loaded. If a
          model is not in the returned dictionary, none of its fields are
          deferred.
  
          If no fields are marked for deferral, return an empty dictionary.
          """
          # We cache this because we call this function multiple times
          # (compiler.fill_related_selections, query.iterator)
          try:
              return self._loaded_field_names_cache
          except AttributeError:
              collection = {}
              self.deferred_to_data(collection, self.get_loaded_field_names_cb)
              self._loaded_field_names_cache = collection
              return collection
  
      def get_loaded_field_names_cb(self, target, model, fields):
          """Callback used by get_deferred_field_names()."""
          target[model] = {f.attname for f in fields}
  
      def set_annotation_mask(self, names):
          """Set the mask of annotations that will be returned by the SELECT."""
          if names is None:
              self.annotation_select_mask = None
          else:
              self.annotation_select_mask = set(names)
          self._annotation_select_cache = None
  
      def append_annotation_mask(self, names):
          if self.annotation_select_mask is not None:
              self.set_annotation_mask(self.annotation_select_mask.union(names))
  
      def set_extra_mask(self, names):
          """
          Set the mask of extra select items that will be returned by SELECT.
          Don't remove them from the Query since they might be used later.
          """
          if names is None:
              self.extra_select_mask = None
          else:
              self.extra_select_mask = set(names)
          self._extra_select_cache = None
  
      def set_values(self, fields):
          self.select_related = False
          self.clear_deferred_loading()
          self.clear_select_fields()
  
          if fields:
              field_names = []
              extra_names = []
              annotation_names = []
              if not self.extra and not self.annotations:
                  # Shortcut - if there are no extra or annotations, then
                  # the values() clause must be just field names.
                  field_names = list(fields)
              else:
                  self.default_cols = False
                  for f in fields:
                      if f in self.extra_select:
                          extra_names.append(f)
                      elif f in self.annotation_select:
                          annotation_names.append(f)
                      else:
                          field_names.append(f)
              self.set_extra_mask(extra_names)
              self.set_annotation_mask(annotation_names)
          else:
              field_names = [f.attname for f in self.model._meta.concrete_fields]
          # Selected annotations must be known before setting the GROUP BY
          # clause.
          if self.group_by is True:
              self.add_fields((f.attname for f in self.model._meta.concrete_fields), False)
              # Disable GROUP BY aliases to avoid orphaning references to the
              # SELECT clause which is about to be cleared.
              self.set_group_by(allow_aliases=False)
              self.clear_select_fields()
          elif self.group_by:
              # Resolve GROUP BY annotation references if they are not part of
              # the selected fields anymore.
              group_by = []
              for expr in self.group_by:
                  if isinstance(expr, Ref) and expr.refs not in field_names:
                      expr = self.annotations[expr.refs]
                  group_by.append(expr)
              self.group_by = tuple(group_by)
  
          self.values_select = tuple(field_names)
          self.add_fields(field_names, True)
  
      @property
      def annotation_select(self):
          """
          Return the dictionary of aggregate columns that are not masked and
          should be used in the SELECT clause. Cache this result for performance.
          """
          if self._annotation_select_cache is not None:
              return self._annotation_select_cache
          elif not self.annotations:
              return {}
          elif self.annotation_select_mask is not None:
              self._annotation_select_cache = {
                  k: v for k, v in self.annotations.items()
                  if k in self.annotation_select_mask
              }
              return self._annotation_select_cache
          else:
              return self.annotations
  
      @property
      def extra_select(self):
          if self._extra_select_cache is not None:
              return self._extra_select_cache
          if not self.extra:
              return {}
          elif self.extra_select_mask is not None:
              self._extra_select_cache = {
                  k: v for k, v in self.extra.items()
                  if k in self.extra_select_mask
              }
              return self._extra_select_cache
          else:
              return self.extra
  
      def trim_start(self, names_with_path):
          """
          Trim joins from the start of the join path. The candidates for trim
          are the PathInfos in names_with_path structure that are m2m joins.
  
          Also set the select column so the start matches the join.
  
          This method is meant to be used for generating the subquery joins &
          cols in split_exclude().
  
          Return a lookup usable for doing outerq.filter(lookup=self) and a
          boolean indicating if the joins in the prefix contain a LEFT OUTER join.
          _"""
          all_paths = []
          for _, paths in names_with_path:
              all_paths.extend(paths)
          contains_louter = False
          # Trim and operate only on tables that were generated for
          # the lookup part of the query. That is, avoid trimming
          # joins generated for F() expressions.
          lookup_tables = [
              t for t in self.alias_map
              if t in self._lookup_joins or t == self.base_table
          ]
          for trimmed_paths, path in enumerate(all_paths):
              if path.m2m:
                  break
              if self.alias_map[lookup_tables[trimmed_paths + 1]].join_type == LOUTER:
                  contains_louter = True
              alias = lookup_tables[trimmed_paths]
              self.unref_alias(alias)
          # The path.join_field is a Rel, lets get the other side's field
          join_field = path.join_field.field
          # Build the filter prefix.
          paths_in_prefix = trimmed_paths
          trimmed_prefix = []
          for name, path in names_with_path:
              if paths_in_prefix - len(path) < 0:
                  break
              trimmed_prefix.append(name)
              paths_in_prefix -= len(path)
          trimmed_prefix.append(
              join_field.foreign_related_fields[0].name)
          trimmed_prefix = LOOKUP_SEP.join(trimmed_prefix)
          # Lets still see if we can trim the first join from the inner query
          # (that is, self). We can't do this for:
          # - LEFT JOINs because we would miss those rows that have nothing on
          #   the outer side,
          # - INNER JOINs from filtered relations because we would miss their
          #   filters.
          first_join = self.alias_map[lookup_tables[trimmed_paths + 1]]
          if first_join.join_type != LOUTER and not first_join.filtered_relation:
              select_fields = [r[0] for r in join_field.related_fields]
              select_alias = lookup_tables[trimmed_paths + 1]
              self.unref_alias(lookup_tables[trimmed_paths])
              extra_restriction = join_field.get_extra_restriction(
                  self.where_class, None, lookup_tables[trimmed_paths + 1])
              if extra_restriction:
                  self.where.add(extra_restriction, AND)
          else:
              # TODO: It might be possible to trim more joins from the start of the
              # inner query if it happens to have a longer join chain containing the
              # values in select_fields. Lets punt this one for now.
              select_fields = [r[1] for r in join_field.related_fields]
              select_alias = lookup_tables[trimmed_paths]
          # The found starting point is likely a Join instead of a BaseTable reference.
          # But the first entry in the query's FROM clause must not be a JOIN.
          for table in self.alias_map:
              if self.alias_refcount[table] > 0:
                  self.alias_map[table] = BaseTable(self.alias_map[table].table_name, table)
                  break
          self.set_select([f.get_col(select_alias) for f in select_fields])
          return trimmed_prefix, contains_louter
  
      def is_nullable(self, field):
          """
          Check if the given field should be treated as nullable.
  
          Some backends treat '' as null and Django treats such fields as
          nullable for those backends. In such situations field.null can be
          False even if we should treat the field as nullable.
          """
          # We need to use DEFAULT_DB_ALIAS here, as QuerySet does not have
          # (nor should it have) knowledge of which connection is going to be
          # used. The proper fix would be to defer all decisions where
          # is_nullable() is needed to the compiler stage, but that is not easy
          # to do currently.
          return (
              connections[DEFAULT_DB_ALIAS].features.interprets_empty_strings_as_nulls and
              field.empty_strings_allowed
          ) or field.null
  
  
  def get_order_dir(field, default='ASC'):
      """
      Return the field name and direction for an order specification. For
      example, '-foo' is returned as ('foo', 'DESC').
  
      The 'default' param is used to indicate which way no prefix (or a '+'
      prefix) should sort. The '-' prefix always sorts the opposite way.
      """
      dirn = ORDER_DIR[default]
      if field[0] == '-':
          return field[1:], dirn[1]
      return field, dirn[0]
  
  
  def add_to_dict(data, key, value):
      """
      Add "value" to the set of values for "key", whether or not "key" already
      exists.
      """
      if key in data:
          data[key].add(value)
      else:
          data[key] = {value}
  
  
  def is_reverse_o2o(field):
      """
      Check if the given field is reverse-o2o. The field is expected to be some
      sort of relation field or related object.
      """
      return field.is_relation and field.one_to_one and not field.concrete
  
  
  class JoinPromoter:
      """
      A class to abstract away join promotion problems for complex filter
      conditions.
      """
  
      def __init__(self, connector, num_children, negated):
          self.connector = connector
          self.negated = negated
          if self.negated:
              if connector == AND:
                  self.effective_connector = OR
              else:
                  self.effective_connector = AND
          else:
              self.effective_connector = self.connector
          self.num_children = num_children
          # Maps of table alias to how many times it is seen as required for
          # inner and/or outer joins.
          self.votes = Counter()
  
      def add_votes(self, votes):
          """
          Add single vote per item to self.votes. Parameter can be any
          iterable.
          """
          self.votes.update(votes)
  
      def update_join_types(self, query):
          """
          Change join types so that the generated query is as efficient as
          possible, but still correct. So, change as many joins as possible
          to INNER, but don't make OUTER joins INNER if that could remove
          results from the query.
          """
          to_promote = set()
          to_demote = set()
          # The effective_connector is used so that NOT (a AND b) is treated
          # similarly to (a OR b) for join promotion.
          for table, votes in self.votes.items():
              # We must use outer joins in OR case when the join isn't contained
              # in all of the joins. Otherwise the INNER JOIN itself could remove
              # valid results. Consider the case where a model with rel_a and
              # rel_b relations is queried with rel_a__col=1 | rel_b__col=2. Now,
              # if rel_a join doesn't produce any results is null (for example
              # reverse foreign key or null value in direct foreign key), and
              # there is a matching row in rel_b with col=2, then an INNER join
              # to rel_a would remove a valid match from the query. So, we need
              # to promote any existing INNER to LOUTER (it is possible this
              # promotion in turn will be demoted later on).
              if self.effective_connector == 'OR' and votes < self.num_children:
                  to_promote.add(table)
              # If connector is AND and there is a filter that can match only
              # when there is a joinable row, then use INNER. For example, in
              # rel_a__col=1 & rel_b__col=2, if either of the rels produce NULL
              # as join output, then the col=1 or col=2 can't match (as
              # NULL=anything is always false).
              # For the OR case, if all children voted for a join to be inner,
              # then we can use INNER for the join. For example:
              #     (rel_a__col__icontains=Alex | rel_a__col__icontains=Russell)
              # then if rel_a doesn't produce any rows, the whole condition
              # can't match. Hence we can safely use INNER join.
              if self.effective_connector == 'AND' or (
                      self.effective_connector == 'OR' and votes == self.num_children):
                  to_demote.add(table)
              # Finally, what happens in cases where we have:
              #    (rel_a__col=1|rel_b__col=2) & rel_a__col__gte=0
              # Now, we first generate the OR clause, and promote joins for it
              # in the first if branch above. Both rel_a and rel_b are promoted
              # to LOUTER joins. After that we do the AND case. The OR case
              # voted no inner joins but the rel_a__col__gte=0 votes inner join
              # for rel_a. We demote it back to INNER join (in AND case a single
              # vote is enough). The demotion is OK, if rel_a doesn't produce
              # rows, then the rel_a__col__gte=0 clause can't be true, and thus
              # the whole clause must be false. So, it is safe to use INNER
              # join.
              # Note that in this example we could just as well have the __gte
              # clause and the OR clause swapped. Or we could replace the __gte
              # clause with an OR clause containing rel_a__col=1|rel_a__col=2,
              # and again we could safely demote to INNER.
          query.promote_joins(to_promote)
          query.demote_joins(to_demote)
          return to_demote
  