text: """
  We perform uniqueness checks explicitly on the serializer class, rather
  the using Django's `.full_clean()`.
  
  This gives us better separation of concerns, allows us to use single-step
  object creation, and makes it possible to switch between using the implicit
  `ModelSerializer` class and an equivalent explicit `Serializer` class.
  """
  from __future__ import unicode_literals
  
  from django.db import DataError
  from django.utils.translation import ugettext_lazy as _
  
  from rest_framework.compat import unicode_to_repr
  from rest_framework.exceptions import ValidationError
  from rest_framework.utils.representation import smart_repr
  
  
  # Robust filter and exist implementations. Ensures that queryset.exists() for
  # an invalid value returns `False`, rather than raising an error.
  # Refs https://github.com/encode/django-rest-framework/issues/3381
  def qs_exists(queryset):
      try:
          return queryset.exists()
      except (TypeError, ValueError, DataError):
          return False
  
  
  def qs_filter(queryset, **kwargs):
      try:
          return queryset.filter(**kwargs)
      except (TypeError, ValueError, DataError):
          return queryset.none()
  
  
  class UniqueValidator(object):
      """
      Validator that corresponds to `unique=True` on a model field.
  
      Should be applied to an individual field on the serializer.
      """
      message = _('This field must be unique.')
  
      def __init__(self, queryset, message=None, lookup='exact'):
          self.queryset = queryset
          self.serializer_field = None
          self.message = message or self.message
          self.lookup = lookup
  
      def set_context(self, serializer_field):
          """
          This hook is called by the serializer instance,
          prior to the validation call being made.
          """
          # Determine the underlying model field name. This may not be the
          # same as the serializer field name if `source=<>` is set.
          self.field_name = serializer_field.source_attrs[-1]
          # Determine the existing instance, if this is an update operation.
          self.instance = getattr(serializer_field.parent, 'instance', None)
  
      def filter_queryset(self, value, queryset):
          """
          Filter the queryset to all instances matching the given attribute.
          """
          filter_kwargs = {'%s__%s' % (self.field_name, self.lookup): value}
          return qs_filter(queryset, **filter_kwargs)
  
      def exclude_current_instance(self, queryset):
          """
          If an instance is being updated, then do not include
          that instance itself as a uniqueness conflict.
          """
          if self.instance is not None:
              return queryset.exclude(pk=self.instance.pk)
          return queryset
  
      def __call__(self, value):
          queryset = self.queryset
          queryset = self.filter_queryset(value, queryset)
          queryset = self.exclude_current_instance(queryset)
          if qs_exists(queryset):
              raise ValidationError(self.message, code='unique')
  
      def __repr__(self):
          return unicode_to_repr('<%s(queryset=%s)>' % (
              self.__class__.__name__,
              smart_repr(self.queryset)
          ))
  
  
  class UniqueTogetherValidator(object):
      """
      Validator that corresponds to `unique_together = (...)` on a model class.
  
      Should be applied to the serializer class, not to an individual field.
      """
      message = _('The fields {field_names} must make a unique set.')
      missing_message = _('This field is required.')
  
      def __init__(self, queryset, fields, message=None):
          self.queryset = queryset
          self.fields = fields
          self.serializer_field = None
          self.message = message or self.message
  
      def set_context(self, serializer):
          """
          This hook is called by the serializer instance,
          prior to the validation call being made.
          """
          # Determine the existing instance, if this is an update operation.
          self.instance = getattr(serializer, 'instance', None)
  
      def enforce_required_fields(self, attrs):
          """
          The `UniqueTogetherValidator` always forces an implied 'required'
          state on the fields it applies to.
          """
          if self.instance is not None:
              return
  
          missing_items = {
              field_name: self.missing_message
              for field_name in self.fields
              if field_name not in attrs
          }
          if missing_items:
              raise ValidationError(missing_items, code='required')
  
      def filter_queryset(self, attrs, queryset):
          """
          Filter the queryset to all instances matching the given attributes.
          """
          # If this is an update, then any unprovided field should
          # have it's value set based on the existing instance attribute.
          if self.instance is not None:
              for field_name in self.fields:
                  if field_name not in attrs:
                      attrs[field_name] = getattr(self.instance, field_name)
  
          # Determine the filter keyword arguments and filter the queryset.
          filter_kwargs = {
              field_name: attrs[field_name]
              for field_name in self.fields
          }
          return qs_filter(queryset, **filter_kwargs)
  
      def exclude_current_instance(self, attrs, queryset):
          """
          If an instance is being updated, then do not include
          that instance itself as a uniqueness conflict.
          """
          if self.instance is not None:
              return queryset.exclude(pk=self.instance.pk)
          return queryset
  
      def __call__(self, attrs):
          self.enforce_required_fields(attrs)
          queryset = self.queryset
          queryset = self.filter_queryset(attrs, queryset)
          queryset = self.exclude_current_instance(attrs, queryset)
  
          # Ignore validation if any field is None
          checked_values = [
              value for field, value in attrs.items() if field in self.fields
          ]
          if None not in checked_values and qs_exists(queryset):
              field_names = ', '.join(self.fields)
              message = self.message.format(field_names=field_names)
              raise ValidationError(message, code='unique')
  
      def __repr__(self):
          return unicode_to_repr('<%s(queryset=%s, fields=%s)>' % (
              self.__class__.__name__,
              smart_repr(self.queryset),
              smart_repr(self.fields)
          ))
  
  
  class BaseUniqueForValidator(object):
      message = None
      missing_message = _('This field is required.')
  
      def __init__(self, queryset, field, date_field, message=None):
          self.queryset = queryset
          self.field = field
          self.date_field = date_field
          self.message = message or self.message
  
      def set_context(self, serializer):
          """
          This hook is called by the serializer instance,
          prior to the validation call being made.
          """
          # Determine the underlying model field names. These may not be the
          # same as the serializer field names if `source=<>` is set.
          self.field_name = serializer.fields[self.field].source_attrs[-1]
          self.date_field_name = serializer.fields[self.date_field].source_attrs[-1]
          # Determine the existing instance, if this is an update operation.
          self.instance = getattr(serializer, 'instance', None)
  
      def enforce_required_fields(self, attrs):
          """
          The `UniqueFor<Range>Validator` classes always force an implied
          'required' state on the fields they are applied to.
          """
          missing_items = {
              field_name: self.missing_message
              for field_name in [self.field, self.date_field]
              if field_name not in attrs
          }
          if missing_items:
              raise ValidationError(missing_items, code='required')
  
      def filter_queryset(self, attrs, queryset):
          raise NotImplementedError('`filter_queryset` must be implemented.')
  
      def exclude_current_instance(self, attrs, queryset):
          """
          If an instance is being updated, then do not include
          that instance itself as a uniqueness conflict.
          """
          if self.instance is not None:
              return queryset.exclude(pk=self.instance.pk)
          return queryset
  
      def __call__(self, attrs):
          self.enforce_required_fields(attrs)
          queryset = self.queryset
          queryset = self.filter_queryset(attrs, queryset)
          queryset = self.exclude_current_instance(attrs, queryset)
          if qs_exists(queryset):
              message = self.message.format(date_field=self.date_field)
              raise ValidationError({
                  self.field: message
              }, code='unique')
  
      def __repr__(self):
          return unicode_to_repr('<%s(queryset=%s, field=%s, date_field=%s)>' % (
              self.__class__.__name__,
              smart_repr(self.queryset),
              smart_repr(self.field),
              smart_repr(self.date_field)
          ))
  
  
  class UniqueForDateValidator(BaseUniqueForValidator):
      message = _('This field must be unique for the "{date_field}" date.')
  
      def filter_queryset(self, attrs, queryset):
          value = attrs[self.field]
          date = attrs[self.date_field]
  
          filter_kwargs = {}
          filter_kwargs[self.field_name] = value
          filter_kwargs['%s__day' % self.date_field_name] = date.day
          filter_kwargs['%s__month' % self.date_field_name] = date.month
          filter_kwargs['%s__year' % self.date_field_name] = date.year
          return qs_filter(queryset, **filter_kwargs)
  
  
  class UniqueForMonthValidator(BaseUniqueForValidator):
      message = _('This field must be unique for the "{date_field}" month.')
  
      def filter_queryset(self, attrs, queryset):
          value = attrs[self.field]
          date = attrs[self.date_field]
  
          filter_kwargs = {}
          filter_kwargs[self.field_name] = value
          filter_kwargs['%s__month' % self.date_field_name] = date.month
          return qs_filter(queryset, **filter_kwargs)
  
  
  class UniqueForYearValidator(BaseUniqueForValidator):
      message = _('This field must be unique for the "{date_field}" year.')
  
      def filter_queryset(self, attrs, queryset):
          value = attrs[self.field]
          date = attrs[self.date_field]
  
          filter_kwargs = {}
          filter_kwargs[self.field_name] = value
          filter_kwargs['%s__year' % self.date_field_name] = date.year
          return qs_filter(queryset, **filter_kwargs)
  