Custom serialization of PrimaryKeyRelatedField values

Adds a 'pk_field' parameter which can be used to proxy serialization and
deserialization of arbitrary primary key values.

docs/api-guide/relations.md

@@ -116,6 +116,8 @@ By default this field is read-write, although you can change this behavior using
 * `queryset` - The queryset used for model instance lookups when validating the field input. Relationships must either set a queryset explicitly, or set `read_only=True`.
 * `many` - If applied to a to-many relationship, you should set this argument to `True`.
 * `allow_null` - If set to `True`, the field will accept values of `None` or the empty string for nullable relationships. Defaults to `False`.
+* `pk_field` - Set to a field to control serialization/deserialization of the primary key's value. For example, `pk_field=UUIDField(format='hex')` would serialize a UUID primary key into its compact hex representation.
+
 
 ## HyperlinkedRelatedField
 

rest_framework/relations.py

@@ -134,10 +134,16 @@ class PrimaryKeyRelatedField(RelatedField):
         'incorrect_type': _('Incorrect type. Expected pk value, received {data_type}.'),
     }
 
+    def __init__(self, **kwargs):
+        self.pk_field = kwargs.pop('pk_field', None)
+        super(PrimaryKeyRelatedField, self).__init__(**kwargs)
+
     def use_pk_only_optimization(self):
         return True
 
     def to_internal_value(self, data):
+        if self.pk_field is not None:
+            data = self.pk_field.to_internal_value(data)
         try:
             return self.get_queryset().get(pk=data)
         except ObjectDoesNotExist:
@@ -146,6 +152,8 @@ class PrimaryKeyRelatedField(RelatedField):
             self.fail('incorrect_type', data_type=type(data).__name__)
 
     def to_representation(self, value):
+        if self.pk_field is not None:
+            return self.pk_field.to_representation(value.pk)
         return value.pk
 
 

tests/test_relations.py

@@ -1,3 +1,4 @@
+import uuid
 from .utils import mock_reverse, fail_reverse, BadType, MockObject, MockQueryset
 from django.core.exceptions import ImproperlyConfigured
 from django.utils.datastructures import MultiValueDict
@@ -48,6 +49,34 @@ class TestPrimaryKeyRelatedField(APISimpleTestCase):
         assert representation == self.instance.pk
 
 
+class TestProxiedPrimaryKeyRelatedField(APISimpleTestCase):
+    def setUp(self):
+        self.queryset = MockQueryset([
+            MockObject(pk=uuid.UUID(int=0), name='foo'),
+            MockObject(pk=uuid.UUID(int=1), name='bar'),
+            MockObject(pk=uuid.UUID(int=2), name='baz')
+        ])
+        self.instance = self.queryset.items[2]
+        self.field = serializers.PrimaryKeyRelatedField(
+            queryset=self.queryset,
+            pk_field=serializers.UUIDField(format='int')
+        )
+
+    def test_pk_related_lookup_exists(self):
+        instance = self.field.to_internal_value(self.instance.pk.int)
+        assert instance is self.instance
+
+    def test_pk_related_lookup_does_not_exist(self):
+        with pytest.raises(serializers.ValidationError) as excinfo:
+            self.field.to_internal_value(4)
+        msg = excinfo.value.detail[0]
+        assert msg == 'Invalid pk "00000000-0000-0000-0000-000000000004" - object does not exist.'
+
+    def test_pk_representation(self):
+        representation = self.field.to_representation(self.instance)
+        assert representation == self.instance.pk.int
+
+
 class TestHyperlinkedIdentityField(APISimpleTestCase):
     def setUp(self):
         self.instance = MockObject(pk=1, name='foo')