text: # Copyright DataStax, Inc.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  # http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  from copy import deepcopy, copy
  from datetime import date, datetime, timedelta
  import logging
  import six
  from uuid import UUID as _UUID
  
  from cassandra import util
  from cassandra.cqltypes import SimpleDateType, _cqltypes, UserType
  from cassandra.cqlengine import ValidationError
  from cassandra.cqlengine.functions import get_total_seconds
  from cassandra.util import Duration as _Duration
  
  log = logging.getLogger(__name__)
  
  
  class BaseValueManager(object):
  
      def __init__(self, instance, column, value):
          self.instance = instance
          self.column = column
          self.value = value
          self.previous_value = None
          self.explicit = False
  
      @property
      def deleted(self):
          return self.column._val_is_null(self.value) and (self.explicit or not self.column._val_is_null(self.previous_value))
  
      @property
      def changed(self):
          """
          Indicates whether or not this value has changed.
  
          :rtype: boolean
  
          """
          if self.explicit:
              return self.value != self.previous_value
  
          if isinstance(self.column, BaseContainerColumn):
              default_value = self.column.get_default()
              if self.column._val_is_null(default_value):
                  return not self.column._val_is_null(self.value) and self.value != self.previous_value
              elif self.previous_value is None:
                  return self.value != default_value
  
              return self.value != self.previous_value
  
          return False
  
      def reset_previous_value(self):
          self.previous_value = deepcopy(self.value)
  
      def getval(self):
          return self.value
  
      def setval(self, val):
          self.value = val
          self.explicit = True
  
      def delval(self):
          self.value = None
  
      def get_property(self):
          _get = lambda slf: self.getval()
          _set = lambda slf, val: self.setval(val)
          _del = lambda slf: self.delval()
  
          if self.column.can_delete:
              return property(_get, _set, _del)
          else:
              return property(_get, _set)
  
  
  class Column(object):
  
      # the cassandra type this column maps to
      db_type = None
      value_manager = BaseValueManager
  
      instance_counter = 0
  
      _python_type_hashable = True
  
      primary_key = False
      """
      bool flag, indicates this column is a primary key. The first primary key defined
      on a model is the partition key (unless partition keys are set), all others are cluster keys
      """
  
      partition_key = False
  
      """
      indicates that this column should be the partition key, defining
      more than one partition key column creates a compound partition key
      """
  
      index = False
      """
      bool flag, indicates an index should be created for this column
      """
  
      custom_index = False
      """
      bool flag, indicates an index is managed outside of cqlengine. This is
      useful if you want to do filter queries on fields that have custom
      indexes.
      """
  
      db_field = None
      """
      the fieldname this field will map to in the database
      """
  
      default = None
      """
      the default value, can be a value or a callable (no args)
      """
  
      required = False
      """
      boolean, is the field required? Model validation will raise and
      exception if required is set to True and there is a None value assigned
      """
  
      clustering_order = None
      """
      only applicable on clustering keys (primary keys that are not partition keys)
      determines the order that the clustering keys are sorted on disk
      """
  
      discriminator_column = False
      """
      boolean, if set to True, this column will be used for discriminating records
      of inherited models.
  
      Should only be set on a column of an abstract model being used for inheritance.
  
      There may only be one discriminator column per model. See :attr:`~.__discriminator_value__`
      for how to specify the value of this column on specialized models.
      """
  
      static = False
      """
      boolean, if set to True, this is a static column, with a single value per partition
      """
  
      def __init__(self,
                   primary_key=False,
                   partition_key=False,
                   index=False,
                   db_field=None,
                   default=None,
                   required=False,
                   clustering_order=None,
                   discriminator_column=False,
                   static=False,
                   custom_index=False):
          self.partition_key = partition_key
          self.primary_key = partition_key or primary_key
          self.index = index
          self.custom_index = custom_index
          self.db_field = db_field
          self.default = default
          self.required = required
          self.clustering_order = clustering_order
          self.discriminator_column = discriminator_column
  
          # the column name in the model definition
          self.column_name = None
          self._partition_key_index = None
          self.static = static
  
          self.value = None
  
          # keep track of instantiation order
          self.position = Column.instance_counter
          Column.instance_counter += 1
  
      def __ne__(self, other):
          if isinstance(other, Column):
              return self.position != other.position
          return NotImplemented
  
      def __eq__(self, other):
          if isinstance(other, Column):
              return self.position == other.position
          return NotImplemented
  
      def __lt__(self, other):
          if isinstance(other, Column):
              return self.position < other.position
          return NotImplemented
  
      def __le__(self, other):
          if isinstance(other, Column):
              return self.position <= other.position
          return NotImplemented
  
      def __gt__(self, other):
          if isinstance(other, Column):
              return self.position > other.position
          return NotImplemented
  
      def __ge__(self, other):
          if isinstance(other, Column):
              return self.position >= other.position
          return NotImplemented
  
      def __hash__(self):
          return id(self)
  
      def validate(self, value):
          """
          Returns a cleaned and validated value. Raises a ValidationError
          if there's a problem
          """
          if value is None:
              if self.required:
                  raise ValidationError('{0} - None values are not allowed'.format(self.column_name or self.db_field))
          return value
  
      def to_python(self, value):
          """
          Converts data from the database into python values
          raises a ValidationError if the value can't be converted
          """
          return value
  
      def to_database(self, value):
          """
          Converts python value into database value
          """
          return value
  
      @property
      def has_default(self):
          return self.default is not None
  
      @property
      def is_primary_key(self):
          return self.primary_key
  
      @property
      def can_delete(self):
          return not self.primary_key
  
      def get_default(self):
          if self.has_default:
              if callable(self.default):
                  return self.default()
              else:
                  return self.default
  
      def get_column_def(self):
          """
          Returns a column definition for CQL table definition
          """
          static = "static" if self.static else ""
          return '{0} {1} {2}'.format(self.cql, self.db_type, static)
  
      # TODO: make columns use cqltypes under the hood
      # until then, this bridges the gap in using types along with cassandra.metadata for CQL generation
      def cql_parameterized_type(self):
          return self.db_type
  
      def set_column_name(self, name):
          """
          Sets the column name during document class construction
          This value will be ignored if db_field is set in __init__
          """
          self.column_name = name
  
      @property
      def db_field_name(self):
          """ Returns the name of the cql name of this column """
          return self.db_field if self.db_field is not None else self.column_name
  
      @property
      def db_index_name(self):
          """ Returns the name of the cql index """
          return 'index_{0}'.format(self.db_field_name)
  
      @property
      def has_index(self):
          return self.index or self.custom_index
  
      @property
      def cql(self):
          return self.get_cql()
  
      def get_cql(self):
          return '"{0}"'.format(self.db_field_name)
  
      def _val_is_null(self, val):
          """ determines if the given value equates to a null value for the given column type """
          return val is None
  
      @property
      def sub_types(self):
          return []
  
      @property
      def cql_type(self):
          return _cqltypes[self.db_type]
  
  
  class Blob(Column):
      """
      Stores a raw binary value
      """
      db_type = 'blob'
  
      def to_database(self, value):
  
          if not isinstance(value, (six.binary_type, bytearray)):
              raise Exception("expecting a binary, got a %s" % type(value))
  
          val = super(Bytes, self).to_database(value)
          return bytearray(val)
  
  
  Bytes = Blob
  
  
  class Inet(Column):
      """
      Stores an IP address in IPv4 or IPv6 format
      """
      db_type = 'inet'
  
  
  class Text(Column):
      """
      Stores a UTF-8 encoded string
      """
      db_type = 'text'
  
      def __init__(self, min_length=None, max_length=None, **kwargs):
          """
          :param int min_length: Sets the minimum length of this string, for validation purposes.
              Defaults to 1 if this is a ``required`` column. Otherwise, None.
          :param int max_length: Sets the maximum length of this string, for validation purposes.
          """
          self.min_length = (
              1 if min_length is None and kwargs.get('required', False)
              else min_length)
          self.max_length = max_length
  
          if self.min_length is not None:
              if self.min_length < 0:
                  raise ValueError(
                      'Minimum length is not allowed to be negative.')
  
          if self.max_length is not None:
              if self.max_length < 0:
                  raise ValueError(
                      'Maximum length is not allowed to be negative.')
  
          if self.min_length is not None and self.max_length is not None:
              if self.max_length < self.min_length:
                  raise ValueError(
                      'Maximum length must be greater or equal '
                      'to minimum length.')
  
          super(Text, self).__init__(**kwargs)
  
      def validate(self, value):
          value = super(Text, self).validate(value)
          if not isinstance(value, (six.string_types, bytearray)) and value is not None:
              raise ValidationError('{0} {1} is not a string'.format(self.column_name, type(value)))
          if self.max_length is not None:
              if value and len(value) > self.max_length:
                  raise ValidationError('{0} is longer than {1} characters'.format(self.column_name, self.max_length))
          if self.min_length:
              if (self.min_length and not value) or len(value) < self.min_length:
                  raise ValidationError('{0} is shorter than {1} characters'.format(self.column_name, self.min_length))
          return value
  
  
  class Ascii(Text):
      """
      Stores a US-ASCII character string
      """
      db_type = 'ascii'
  
      def validate(self, value):
          """ Only allow ASCII and None values.
  
          Check against US-ASCII, a.k.a. 7-bit ASCII, a.k.a. ISO646-US, a.k.a.
          the Basic Latin block of the Unicode character set.
  
          Source: https://github.com/apache/cassandra/blob
          /3dcbe90e02440e6ee534f643c7603d50ca08482b/src/java/org/apache/cassandra
          /serializers/AsciiSerializer.java#L29
          """
          value = super(Ascii, self).validate(value)
          if value:
              charset = value if isinstance(
                  value, (bytearray, )) else map(ord, value)
              if not set(range(128)).issuperset(charset):
                  raise ValidationError(
                      '{!r} is not an ASCII string.'.format(value))
          return value
  
  
  class Integer(Column):
      """
      Stores a 32-bit signed integer value
      """
  
      db_type = 'int'
  
      def validate(self, value):
          val = super(Integer, self).validate(value)
          if val is None:
              return
          try:
              return int(val)
          except (TypeError, ValueError):
              raise ValidationError("{0} {1} can't be converted to integral value".format(self.column_name, value))
  
      def to_python(self, value):
          return self.validate(value)
  
      def to_database(self, value):
          return self.validate(value)
  
  
  class TinyInt(Integer):
      """
      Stores an 8-bit signed integer value
  
      .. versionadded:: 2.6.0
  
      requires C* 2.2+ and protocol v4+
      """
      db_type = 'tinyint'
  
  
  class SmallInt(Integer):
      """
      Stores a 16-bit signed integer value
  
      .. versionadded:: 2.6.0
  
      requires C* 2.2+ and protocol v4+
      """
      db_type = 'smallint'
  
  
  class BigInt(Integer):
      """
      Stores a 64-bit signed integer value
      """
      db_type = 'bigint'
  
  
  class VarInt(Column):
      """
      Stores an arbitrary-precision integer
      """
      db_type = 'varint'
  
      def validate(self, value):
          val = super(VarInt, self).validate(value)
          if val is None:
              return
          try:
              return int(val)
          except (TypeError, ValueError):
              raise ValidationError(
                  "{0} {1} can't be converted to integral value".format(self.column_name, value))
  
      def to_python(self, value):
          return self.validate(value)
  
      def to_database(self, value):
          return self.validate(value)
  
  
  class CounterValueManager(BaseValueManager):
      def __init__(self, instance, column, value):
          super(CounterValueManager, self).__init__(instance, column, value)
          self.value = self.value or 0
          self.previous_value = self.previous_value or 0
  
  
  class Counter(Integer):
      """
      Stores a counter that can be incremented and decremented
      """
      db_type = 'counter'
  
      value_manager = CounterValueManager
  
      def __init__(self,
                   index=False,
                   db_field=None,
                   required=False):
          super(Counter, self).__init__(
              primary_key=False,
              partition_key=False,
              index=index,
              db_field=db_field,
              default=0,
              required=required,
          )
  
  
  class DateTime(Column):
      """
      Stores a datetime value
      """
      db_type = 'timestamp'
  
      truncate_microseconds = False
      """
      Set this ``True`` to have model instances truncate the date, quantizing it in the same way it will be in the database.
      This allows equality comparison between assigned values and values read back from the database::
  
          DateTime.truncate_microseconds = True
          assert Model.create(id=0, d=datetime.utcnow()) == Model.objects(id=0).first()
  
      Defaults to ``False`` to preserve legacy behavior. May change in the future.
      """
  
      def to_python(self, value):
          if value is None:
              return
          if isinstance(value, datetime):
              if DateTime.truncate_microseconds:
                  us = value.microsecond
                  truncated_us = us // 1000 * 1000
                  return value - timedelta(microseconds=us - truncated_us)
              else:
                  return value
          elif isinstance(value, date):
              return datetime(*(value.timetuple()[:6]))
  
          return datetime.utcfromtimestamp(value)
  
      def to_database(self, value):
          value = super(DateTime, self).to_database(value)
          if value is None:
              return
          if not isinstance(value, datetime):
              if isinstance(value, date):
                  value = datetime(value.year, value.month, value.day)
              else:
                  raise ValidationError("{0} '{1}' is not a datetime object".format(self.column_name, value))
          epoch = datetime(1970, 1, 1, tzinfo=value.tzinfo)
          offset = get_total_seconds(epoch.tzinfo.utcoffset(epoch)) if epoch.tzinfo else 0
  
          return int((get_total_seconds(value - epoch) - offset) * 1000)
  
  
  class Date(Column):
      """
      Stores a simple date, with no time-of-day
  
      .. versionchanged:: 2.6.0
  
          removed overload of Date and DateTime. DateTime is a drop-in replacement for legacy models
  
      requires C* 2.2+ and protocol v4+
      """
      db_type = 'date'
  
      def to_database(self, value):
          if value is None:
              return
  
          # need to translate to int version because some dates are not representable in
          # string form (datetime limitation)
          d = value if isinstance(value, util.Date) else util.Date(value)
          return d.days_from_epoch + SimpleDateType.EPOCH_OFFSET_DAYS
  
      def to_python(self, value):
          if value is None:
              return
          if isinstance(value, util.Date):
              return value
          if isinstance(value, datetime):
              value = value.date()
          return util.Date(value)
  
  class Time(Column):
      """
      Stores a timezone-naive time-of-day, with nanosecond precision
  
      .. versionadded:: 2.6.0
  
      requires C* 2.2+ and protocol v4+
      """
      db_type = 'time'
  
      def to_database(self, value):
          value = super(Time, self).to_database(value)
          if value is None:
              return
          # str(util.Time) yields desired CQL encoding
          return value if isinstance(value, util.Time) else util.Time(value)
  
      def to_python(self, value):
          value = super(Time, self).to_database(value)
          if value is None:
              return
          if isinstance(value, util.Time):
              return value
          return util.Time(value)
  
  class Duration(Column):
      """
      Stores a duration (months, days, nanoseconds)
  
      .. versionadded:: 3.10.0
  
      requires C* 3.10+ and protocol v4+
      """
      db_type = 'duration'
  
      def validate(self, value):
          val = super(Duration, self).validate(value)
          if val is None:
              return
          if not isinstance(val, _Duration):
              raise TypeError('{0} {1} is not a valid Duration.'.format(self.column_name, value))
          return val
  
  
  class UUID(Column):
      """
      Stores a type 1 or 4 UUID
      """
      db_type = 'uuid'
  
      def validate(self, value):
          val = super(UUID, self).validate(value)
          if val is None:
              return
          if isinstance(val, _UUID):
              return val
          if isinstance(val, six.string_types):
              try:
                  return _UUID(val)
              except ValueError:
                  # fall-through to error
                  pass
          raise ValidationError("{0} {1} is not a valid uuid".format(
              self.column_name, value))
  
      def to_python(self, value):
          return self.validate(value)
  
      def to_database(self, value):
          return self.validate(value)
  
  
  class TimeUUID(UUID):
      """
      UUID containing timestamp
      """
  
      db_type = 'timeuuid'
  
  
  class Boolean(Column):
      """
      Stores a boolean True or False value
      """
      db_type = 'boolean'
  
      def validate(self, value):
          """ Always returns a Python boolean. """
          value = super(Boolean, self).validate(value)
  
          if value is not None:
              value = bool(value)
  
          return value
  
      def to_python(self, value):
          return self.validate(value)
  
  
  class BaseFloat(Column):
      def validate(self, value):
          value = super(BaseFloat, self).validate(value)
          if value is None:
              return
          try:
              return float(value)
          except (TypeError, ValueError):
              raise ValidationError("{0} {1} is not a valid float".format(self.column_name, value))
  
      def to_python(self, value):
          return self.validate(value)
  
      def to_database(self, value):
          return self.validate(value)
  
  
  class Float(BaseFloat):
      """
      Stores a single-precision floating-point value
      """
      db_type = 'float'
  
  
  class Double(BaseFloat):
      """
      Stores a double-precision floating-point value
      """
      db_type = 'double'
  
  
  class Decimal(Column):
      """
      Stores a variable precision decimal value
      """
      db_type = 'decimal'
  
      def validate(self, value):
          from decimal import Decimal as _Decimal
          from decimal import InvalidOperation
          val = super(Decimal, self).validate(value)
          if val is None:
              return
          try:
              return _Decimal(repr(val)) if isinstance(val, float) else _Decimal(val)
          except InvalidOperation:
              raise ValidationError("{0} '{1}' can't be coerced to decimal".format(self.column_name, val))
  
      def to_python(self, value):
          return self.validate(value)
  
      def to_database(self, value):
          return self.validate(value)
  
  
  class BaseCollectionColumn(Column):
      """
      Base Container type for collection-like columns.
  
      http://cassandra.apache.org/doc/cql3/CQL-3.0.html#collections
      """
      def __init__(self, types, **kwargs):
          """
          :param types: a sequence of sub types in this collection
          """
          instances = []
          for t in types:
              inheritance_comparator = issubclass if isinstance(t, type) else isinstance
              if not inheritance_comparator(t, Column):
                  raise ValidationError("%s is not a column class" % (t,))
              if t.db_type is None:
                  raise ValidationError("%s is an abstract type" % (t,))
              inst = t() if isinstance(t, type) else t
              if isinstance(t, BaseCollectionColumn):
                  inst._freeze_db_type()
              instances.append(inst)
  
          self.types = instances
          super(BaseCollectionColumn, self).__init__(**kwargs)
  
      def validate(self, value):
          value = super(BaseCollectionColumn, self).validate(value)
          # It is dangerous to let collections have more than 65535.
          # See: https://issues.apache.org/jira/browse/CASSANDRA-5428
          if value is not None and len(value) > 65535:
              raise ValidationError("{0} Collection can't have more than 65535 elements.".format(self.column_name))
          return value
  
      def _val_is_null(self, val):
          return not val
  
      def _freeze_db_type(self):
          if not self.db_type.startswith('frozen'):
              self.db_type = "frozen<%s>" % (self.db_type,)
  
      @property
      def sub_types(self):
          return self.types
  
      @property
      def cql_type(self):
          return _cqltypes[self.__class__.__name__.lower()].apply_parameters([c.cql_type for c in self.types])
  
  
  class Tuple(BaseCollectionColumn):
      """
      Stores a fixed-length set of positional values
  
      http://docs.datastax.com/en/cql/3.1/cql/cql_reference/tupleType.html
      """
      def __init__(self, *args, **kwargs):
          """
          :param args: column types representing tuple composition
          """
          if not args:
              raise ValueError("Tuple must specify at least one inner type")
          super(Tuple, self).__init__(args, **kwargs)
          self.db_type = 'tuple<{0}>'.format(', '.join(typ.db_type for typ in self.types))
  
      def validate(self, value):
          val = super(Tuple, self).validate(value)
          if val is None:
              return
          if len(val) > len(self.types):
              raise ValidationError("Value %r has more fields than tuple definition (%s)" %
                                    (val, ', '.join(t for t in self.types)))
          return tuple(t.validate(v) for t, v in zip(self.types, val))
  
      def to_python(self, value):
          if value is None:
              return tuple()
          return tuple(t.to_python(v) for t, v in zip(self.types, value))
  
      def to_database(self, value):
          if value is None:
              return
          return tuple(t.to_database(v) for t, v in zip(self.types, value))
  
  
  class BaseContainerColumn(BaseCollectionColumn):
      pass
  
  
  class Set(BaseContainerColumn):
      """
      Stores a set of unordered, unique values
  
      http://www.datastax.com/documentation/cql/3.1/cql/cql_using/use_set_t.html
      """
  
      _python_type_hashable = False
  
      def __init__(self, value_type, strict=True, default=set, **kwargs):
          """
          :param value_type: a column class indicating the types of the value
          :param strict: sets whether non set values will be coerced to set
              type on validation, or raise a validation error, defaults to True
          """
          self.strict = strict
          super(Set, self).__init__((value_type,), default=default, **kwargs)
          self.value_col = self.types[0]
          if not self.value_col._python_type_hashable:
              raise ValidationError("Cannot create a Set with unhashable value type (see PYTHON-494)")
          self.db_type = 'set<{0}>'.format(self.value_col.db_type)
  
      def validate(self, value):
          val = super(Set, self).validate(value)
          if val is None:
              return
          types = (set, util.SortedSet) if self.strict else (set, util.SortedSet, list, tuple)
          if not isinstance(val, types):
              if self.strict:
                  raise ValidationError('{0} {1} is not a set object'.format(self.column_name, val))
              else:
                  raise ValidationError('{0} {1} cannot be coerced to a set object'.format(self.column_name, val))
  
          if None in val:
              raise ValidationError("{0} None not allowed in a set".format(self.column_name))
          # TODO: stop doing this conversion because it doesn't support non-hashable collections as keys (cassandra does)
          # will need to start using the cassandra.util types in the next major rev (PYTHON-494)
          return set(self.value_col.validate(v) for v in val)
  
      def to_python(self, value):
          if value is None:
              return set()
          return set(self.value_col.to_python(v) for v in value)
  
      def to_database(self, value):
          if value is None:
              return None
          return set(self.value_col.to_database(v) for v in value)
  
  
  class List(BaseContainerColumn):
      """
      Stores a list of ordered values
  
      http://www.datastax.com/documentation/cql/3.1/cql/cql_using/use_list_t.html
      """
  
      _python_type_hashable = False
  
      def __init__(self, value_type, default=list, **kwargs):
          """
          :param value_type: a column class indicating the types of the value
          """
          super(List, self).__init__((value_type,), default=default, **kwargs)
          self.value_col = self.types[0]
          self.db_type = 'list<{0}>'.format(self.value_col.db_type)
  
      def validate(self, value):
          val = super(List, self).validate(value)
          if val is None:
              return
          if not isinstance(val, (set, list, tuple)):
              raise ValidationError('{0} {1} is not a list object'.format(self.column_name, val))
          if None in val:
              raise ValidationError("{0} None is not allowed in a list".format(self.column_name))
          return [self.value_col.validate(v) for v in val]
  
      def to_python(self, value):
          if value is None:
              return []
          return [self.value_col.to_python(v) for v in value]
  
      def to_database(self, value):
          if value is None:
              return None
          return [self.value_col.to_database(v) for v in value]
  
  
  class Map(BaseContainerColumn):
      """
      Stores a key -> value map (dictionary)
  
      https://docs.datastax.com/en/dse/6.7/cql/cql/cql_using/useMap.html
      """
  
      _python_type_hashable = False
  
      def __init__(self, key_type, value_type, default=dict, **kwargs):
          """
          :param key_type: a column class indicating the types of the key
          :param value_type: a column class indicating the types of the value
          """
          super(Map, self).__init__((key_type, value_type), default=default, **kwargs)
          self.key_col = self.types[0]
          self.value_col = self.types[1]
  
          if not self.key_col._python_type_hashable:
              raise ValidationError("Cannot create a Map with unhashable key type (see PYTHON-494)")
  
          self.db_type = 'map<{0}, {1}>'.format(self.key_col.db_type, self.value_col.db_type)
  
      def validate(self, value):
          val = super(Map, self).validate(value)
          if val is None:
              return
          if not isinstance(val, (dict, util.OrderedMap)):
              raise ValidationError('{0} {1} is not a dict object'.format(self.column_name, val))
          if None in val:
              raise ValidationError("{0} None is not allowed in a map".format(self.column_name))
          # TODO: stop doing this conversion because it doesn't support non-hashable collections as keys (cassandra does)
          # will need to start using the cassandra.util types in the next major rev (PYTHON-494)
          return dict((self.key_col.validate(k), self.value_col.validate(v)) for k, v in val.items())
  
      def to_python(self, value):
          if value is None:
              return {}
          if value is not None:
              return dict((self.key_col.to_python(k), self.value_col.to_python(v)) for k, v in value.items())
  
      def to_database(self, value):
          if value is None:
              return None
          return dict((self.key_col.to_database(k), self.value_col.to_database(v)) for k, v in value.items())
  
  
  class UDTValueManager(BaseValueManager):
      @property
      def changed(self):
          if self.explicit:
              return self.value != self.previous_value
  
          default_value = self.column.get_default()
          if not self.column._val_is_null(default_value):
              return self.value != default_value
          elif self.previous_value is None:
              return not self.column._val_is_null(self.value) and self.value.has_changed_fields()
  
          return False
  
      def reset_previous_value(self):
          if self.value is not None:
              self.value.reset_changed_fields()
          self.previous_value = copy(self.value)
  
  
  class UserDefinedType(Column):
      """
      User Defined Type column
  
      http://www.datastax.com/documentation/cql/3.1/cql/cql_using/cqlUseUDT.html
  
      These columns are represented by a specialization of :class:`cassandra.cqlengine.usertype.UserType`.
  
      Please see :ref:`user_types` for examples and discussion.
      """
  
      value_manager = UDTValueManager
  
      def __init__(self, user_type, **kwargs):
          """
          :param type user_type: specifies the :class:`~.cqlengine.usertype.UserType` model of the column
          """
          self.user_type = user_type
          self.db_type = "frozen<%s>" % user_type.type_name()
          super(UserDefinedType, self).__init__(**kwargs)
  
      @property
      def sub_types(self):
          return list(self.user_type._fields.values())
  
      @property
      def cql_type(self):
          return UserType.make_udt_class(keyspace='', udt_name=self.user_type.type_name(),
                                         field_names=[c.db_field_name for c in self.user_type._fields.values()],
                                         field_types=[c.cql_type for c in self.user_type._fields.values()])
  
      def validate(self, value):
          val = super(UserDefinedType, self).validate(value)
          if val is None:
              return
          val.validate()
          return val
  
      def to_python(self, value):
          if value is None:
              return
  
          copied_value = deepcopy(value)
  
          for name, field in self.user_type._fields.items():
              try:
                  if copied_value[name] is not None or isinstance(field, BaseContainerColumn):
                      copied_value[name] = field.to_python(copied_value[name])
              except TypeError as e:
                  pass
  
          return copied_value
  
      def to_database(self, value):
          if value is None:
              return
  
          copied_value = deepcopy(value)
          for name, field in self.user_type._fields.items():
              if copied_value[name] is not None or isinstance(field, BaseContainerColumn):
                  copied_value[name] = field.to_database(copied_value[name])
  
          return copied_value
  
  
  def resolve_udts(col_def, out_list):
      for col in col_def.sub_types:
          resolve_udts(col, out_list)
      if isinstance(col_def, UserDefinedType):
          out_list.append(col_def.user_type)
  
  
  class _PartitionKeysToken(Column):
      """
      virtual column representing token of partition columns.
      Used by filter(pk__token=Token(...)) filters
      """
  
      def __init__(self, model):
          self.partition_columns = list(model._partition_keys.values())
          super(_PartitionKeysToken, self).__init__(partition_key=True)
  
      @property
      def db_field_name(self):
          return 'token({0})'.format(', '.join(['"{0}"'.format(c.db_field_name) for c in self.partition_columns]))
  