text: import sys
  
  from django.contrib.contenttypes.generic import GenericForeignKey, GenericRelation
  from django.core.management.color import color_style
  from django.utils.itercompat import is_iterable
  
  try:
      any
  except NameError:
      from django.utils.itercompat import any
  
  class ModelErrorCollection:
      def __init__(self, outfile=sys.stdout):
          self.errors = []
          self.outfile = outfile
          self.style = color_style()
  
      def add(self, context, error):
          self.errors.append((context, error))
          self.outfile.write(self.style.ERROR("%s: %s\n" % (context, error)))
  
  def get_validation_errors(outfile, app=None):
      """
      Validates all models that are part of the specified app. If no app name is provided,
      validates all models of all installed apps. Writes errors, if any, to outfile.
      Returns number of errors.
      """
      from django.conf import settings
      from django.db import models, connection
      from django.db.models.loading import get_app_errors
      from django.db.models.fields.related import RelatedObject
      from django.db.models.deletion import SET_NULL, SET_DEFAULT
  
      e = ModelErrorCollection(outfile)
  
      for (app_name, error) in get_app_errors().items():
          e.add(app_name, error)
  
      for cls in models.get_models(app):
          opts = cls._meta
  
          # Do field-specific validation.
          for f in opts.local_fields:
              if f.name == 'id' and not f.primary_key and opts.pk.name == 'id':
                  e.add(opts, '"%s": You can\'t use "id" as a field name, because each model automatically gets an "id" field if none of the fields have primary_key=True. You need to either remove/rename your "id" field or add primary_key=True to a field.' % f.name)
              if f.name.endswith('_'):
                  e.add(opts, '"%s": Field names cannot end with underscores, because this would lead to ambiguous queryset filters.' % f.name)
              if isinstance(f, models.CharField):
                  try:
                      max_length = int(f.max_length)
                      if max_length <= 0:
                          e.add(opts, '"%s": CharFields require a "max_length" attribute that is a positive integer.' % f.name)
                  except (ValueError, TypeError):
                      e.add(opts, '"%s": CharFields require a "max_length" attribute that is a positive integer.' % f.name)
              if isinstance(f, models.DecimalField):
                  decimalp_ok, mdigits_ok = False, False
                  decimalp_msg ='"%s": DecimalFields require a "decimal_places" attribute that is a non-negative integer.'
                  try:
                      decimal_places = int(f.decimal_places)
                      if decimal_places < 0:
                          e.add(opts, decimalp_msg % f.name)
                      else:
                          decimalp_ok = True
                  except (ValueError, TypeError):
                      e.add(opts, decimalp_msg % f.name)
                  mdigits_msg = '"%s": DecimalFields require a "max_digits" attribute that is a positive integer.'
                  try:
                      max_digits = int(f.max_digits)
                      if max_digits <= 0:
                          e.add(opts,  mdigits_msg % f.name)
                      else:
                          mdigits_ok = True
                  except (ValueError, TypeError):
                      e.add(opts, mdigits_msg % f.name)
                  invalid_values_msg = '"%s": DecimalFields require a "max_digits" attribute value that is greater than the value of the "decimal_places" attribute.'
                  if decimalp_ok and mdigits_ok:
                      if decimal_places >= max_digits:
                          e.add(opts, invalid_values_msg % f.name)
              if isinstance(f, models.FileField) and not f.upload_to:
                  e.add(opts, '"%s": FileFields require an "upload_to" attribute.' % f.name)
              if isinstance(f, models.ImageField):
                  # Try to import PIL in either of the two ways it can end up installed.
                  try:
                      from PIL import Image
                  except ImportError:
                      try:
                          import Image
                      except ImportError:
                          e.add(opts, '"%s": To use ImageFields, you need to install the Python Imaging Library. Get it at http://www.pythonware.com/products/pil/ .' % f.name)
              if isinstance(f, models.BooleanField) and getattr(f, 'null', False):
                  e.add(opts, '"%s": BooleanFields do not accept null values. Use a NullBooleanField instead.' % f.name)
              if f.choices:
                  if isinstance(f.choices, basestring) or not is_iterable(f.choices):
                      e.add(opts, '"%s": "choices" should be iterable (e.g., a tuple or list).' % f.name)
                  else:
                      for c in f.choices:
                          if not isinstance(c, (list, tuple)) or len(c) != 2:
                              e.add(opts, '"%s": "choices" should be a sequence of two-tuples.' % f.name)
              if f.db_index not in (None, True, False):
                  e.add(opts, '"%s": "db_index" should be either None, True or False.' % f.name)
  
              # Perform any backend-specific field validation.
              connection.validation.validate_field(e, opts, f)
  
              # Check if the on_delete behavior is sane
              if f.rel and hasattr(f.rel, 'on_delete'):
                  if f.rel.on_delete == SET_NULL and not f.null:
                      e.add(opts, "'%s' specifies on_delete=SET_NULL, but cannot be null." % f.name)
                  elif f.rel.on_delete == SET_DEFAULT and not f.has_default():
                      e.add(opts, "'%s' specifies on_delete=SET_DEFAULT, but has no default value." % f.name)
  
              # Check to see if the related field will clash with any existing
              # fields, m2m fields, m2m related objects or related objects
              if f.rel:
                  if f.rel.to not in models.get_models():
                      e.add(opts, "'%s' has a relation with model %s, which has either not been installed or is abstract." % (f.name, f.rel.to))
                  # it is a string and we could not find the model it refers to
                  # so skip the next section
                  if isinstance(f.rel.to, (str, unicode)):
                      continue
  
                  # Make sure the related field specified by a ForeignKey is unique
                  if not f.rel.to._meta.get_field(f.rel.field_name).unique:
                      e.add(opts, "Field '%s' under model '%s' must have a unique=True constraint." % (f.rel.field_name, f.rel.to.__name__))
  
                  rel_opts = f.rel.to._meta
                  rel_name = RelatedObject(f.rel.to, cls, f).get_accessor_name()
                  rel_query_name = f.related_query_name()
                  if not f.rel.is_hidden():
                      for r in rel_opts.fields:
                          if r.name == rel_name:
                              e.add(opts, "Accessor for field '%s' clashes with field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
                          if r.name == rel_query_name:
                              e.add(opts, "Reverse query name for field '%s' clashes with field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
                      for r in rel_opts.local_many_to_many:
                          if r.name == rel_name:
                              e.add(opts, "Accessor for field '%s' clashes with m2m field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
                          if r.name == rel_query_name:
                              e.add(opts, "Reverse query name for field '%s' clashes with m2m field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
                      for r in rel_opts.get_all_related_many_to_many_objects():
                          if r.get_accessor_name() == rel_name:
                              e.add(opts, "Accessor for field '%s' clashes with related m2m field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.get_accessor_name(), f.name))
                          if r.get_accessor_name() == rel_query_name:
                              e.add(opts, "Reverse query name for field '%s' clashes with related m2m field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.get_accessor_name(), f.name))
                      for r in rel_opts.get_all_related_objects():
                          if r.field is not f:
                              if r.get_accessor_name() == rel_name:
                                  e.add(opts, "Accessor for field '%s' clashes with related field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.get_accessor_name(), f.name))
                              if r.get_accessor_name() == rel_query_name:
                                  e.add(opts, "Reverse query name for field '%s' clashes with related field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.get_accessor_name(), f.name))
  
          seen_intermediary_signatures = []
          for i, f in enumerate(opts.local_many_to_many):
              # Check to see if the related m2m field will clash with any
              # existing fields, m2m fields, m2m related objects or related
              # objects
              if f.rel.to not in models.get_models():
                  e.add(opts, "'%s' has an m2m relation with model %s, which has either not been installed or is abstract." % (f.name, f.rel.to))
                  # it is a string and we could not find the model it refers to
                  # so skip the next section
                  if isinstance(f.rel.to, (str, unicode)):
                      continue
  
              # Check that the field is not set to unique.  ManyToManyFields do not support unique.
              if f.unique:
                  e.add(opts, "ManyToManyFields cannot be unique.  Remove the unique argument on '%s'." % f.name)
  
              if f.rel.through is not None and not isinstance(f.rel.through, basestring):
                  from_model, to_model = cls, f.rel.to
                  if from_model == to_model and f.rel.symmetrical and not f.rel.through._meta.auto_created:
                      e.add(opts, "Many-to-many fields with intermediate tables cannot be symmetrical.")
                  seen_from, seen_to, seen_self = False, False, 0
                  for inter_field in f.rel.through._meta.fields:
                      rel_to = getattr(inter_field.rel, 'to', None)
                      if from_model == to_model: # relation to self
                          if rel_to == from_model:
                              seen_self += 1
                          if seen_self > 2:
                              e.add(opts, "Intermediary model %s has more than "
                                  "two foreign keys to %s, which is ambiguous "
                                  "and is not permitted." % (
                                      f.rel.through._meta.object_name,
                                      from_model._meta.object_name
                                  )
                              )
                      else:
                          if rel_to == from_model:
                              if seen_from:
                                  e.add(opts, "Intermediary model %s has more "
                                      "than one foreign key to %s, which is "
                                      "ambiguous and is not permitted." % (
                                          f.rel.through._meta.object_name,
                                           from_model._meta.object_name
                                       )
                                   )
                              else:
                                  seen_from = True
                          elif rel_to == to_model:
                              if seen_to:
                                  e.add(opts, "Intermediary model %s has more "
                                      "than one foreign key to %s, which is "
                                      "ambiguous and is not permitted." % (
                                          f.rel.through._meta.object_name,
                                          rel_to._meta.object_name
                                      )
                                  )
                              else:
                                  seen_to = True
                  if f.rel.through not in models.get_models(include_auto_created=True):
                      e.add(opts, "'%s' specifies an m2m relation through model "
                          "%s, which has not been installed." % (f.name, f.rel.through)
                      )
                  signature = (f.rel.to, cls, f.rel.through)
                  if signature in seen_intermediary_signatures:
                      e.add(opts, "The model %s has two manually-defined m2m "
                          "relations through the model %s, which is not "
                          "permitted. Please consider using an extra field on "
                          "your intermediary model instead." % (
                              cls._meta.object_name,
                              f.rel.through._meta.object_name
                          )
                      )
                  else:
                      seen_intermediary_signatures.append(signature)
                  if not f.rel.through._meta.auto_created:
                      seen_related_fk, seen_this_fk = False, False
                      for field in f.rel.through._meta.fields:
                          if field.rel:
                              if not seen_related_fk and field.rel.to == f.rel.to:
                                  seen_related_fk = True
                              elif field.rel.to == cls:
                                  seen_this_fk = True
                      if not seen_related_fk or not seen_this_fk:
                          e.add(opts, "'%s' is a manually-defined m2m relation "
                              "through model %s, which does not have foreign keys "
                              "to %s and %s" % (f.name, f.rel.through._meta.object_name,
                                  f.rel.to._meta.object_name, cls._meta.object_name)
                          )
              elif isinstance(f.rel.through, basestring):
                  e.add(opts, "'%s' specifies an m2m relation through model %s, "
                      "which has not been installed" % (f.name, f.rel.through)
                  )
              elif isinstance(f, GenericRelation):
                  if not any([isinstance(vfield, GenericForeignKey) for vfield in f.rel.to._meta.virtual_fields]):
                      e.add(opts, "Model '%s' must have a GenericForeignKey in "
                          "order to create a GenericRelation that points to it."
                          % f.rel.to.__name__
                      )
  
              rel_opts = f.rel.to._meta
              rel_name = RelatedObject(f.rel.to, cls, f).get_accessor_name()
              rel_query_name = f.related_query_name()
              # If rel_name is none, there is no reverse accessor (this only
              # occurs for symmetrical m2m relations to self). If this is the
              # case, there are no clashes to check for this field, as there are
              # no reverse descriptors for this field.
              if rel_name is not None:
                  for r in rel_opts.fields:
                      if r.name == rel_name:
                          e.add(opts, "Accessor for m2m field '%s' clashes with field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
                      if r.name == rel_query_name:
                          e.add(opts, "Reverse query name for m2m field '%s' clashes with field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
                  for r in rel_opts.local_many_to_many:
                      if r.name == rel_name:
                          e.add(opts, "Accessor for m2m field '%s' clashes with m2m field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
                      if r.name == rel_query_name:
                          e.add(opts, "Reverse query name for m2m field '%s' clashes with m2m field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.name, f.name))
                  for r in rel_opts.get_all_related_many_to_many_objects():
                      if r.field is not f:
                          if r.get_accessor_name() == rel_name:
                              e.add(opts, "Accessor for m2m field '%s' clashes with related m2m field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.get_accessor_name(), f.name))
                          if r.get_accessor_name() == rel_query_name:
                              e.add(opts, "Reverse query name for m2m field '%s' clashes with related m2m field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.get_accessor_name(), f.name))
                  for r in rel_opts.get_all_related_objects():
                      if r.get_accessor_name() == rel_name:
                          e.add(opts, "Accessor for m2m field '%s' clashes with related field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.get_accessor_name(), f.name))
                      if r.get_accessor_name() == rel_query_name:
                          e.add(opts, "Reverse query name for m2m field '%s' clashes with related field '%s.%s'. Add a related_name argument to the definition for '%s'." % (f.name, rel_opts.object_name, r.get_accessor_name(), f.name))
  
          # Check ordering attribute.
          if opts.ordering:
              for field_name in opts.ordering:
                  if field_name == '?': continue
                  if field_name.startswith('-'):
                      field_name = field_name[1:]
                  if opts.order_with_respect_to and field_name == '_order':
                      continue
                  # Skip ordering in the format field1__field2 (FIXME: checking
                  # this format would be nice, but it's a little fiddly).
                  if '__' in field_name:
                      continue
                  try:
                      opts.get_field(field_name, many_to_many=False)
                  except models.FieldDoesNotExist:
                      e.add(opts, '"ordering" refers to "%s", a field that doesn\'t exist.' % field_name)
  
          # Check unique_together.
          for ut in opts.unique_together:
              for field_name in ut:
                  try:
                      f = opts.get_field(field_name, many_to_many=True)
                  except models.FieldDoesNotExist:
                      e.add(opts, '"unique_together" refers to %s, a field that doesn\'t exist. Check your syntax.' % field_name)
                  else:
                      if isinstance(f.rel, models.ManyToManyRel):
                          e.add(opts, '"unique_together" refers to %s. ManyToManyFields are not supported in unique_together.' % f.name)
                      if f not in opts.local_fields:
                          e.add(opts, '"unique_together" refers to %s. This is not in the same model as the unique_together statement.' % f.name)
  
      return len(e.errors)
  