  
  from rest_framework import serializers
  from tests.models import (
      ForeignKeySource, ForeignKeyTarget, ManyToManySource, ManyToManyTarget,
      NullableForeignKeySource, NullableOneToOneSource,
      NullableUUIDForeignKeySource, OneToOneTarget, UUIDForeignKeyTarget
  )
  
  
  # ManyToMany
 
</s>
    NullableForeignKeySource, NullableOneToOneSource, OneToOnePKSource,
  
  from rest_framework import serializers
  from tests.models import (
      ForeignKeySource, ForeignKeyTarget, ManyToManySource, ManyToManyTarget,
    NullableForeignKeySource, NullableOneToOneSource, OneToOnePKSource,
      NullableUUIDForeignKeySource, OneToOneTarget, UUIDForeignKeyTarget
  )
  
  
  # ManyToMany
keep keep keep keep replace keep keep keep keep keep
 Special case for when OneToOneField is also primary key.

https://github.com/encode/django-rest-framework/issues/5135
tests/test_relations_pk.py