Handle ModelSerializer case for relationships to models with custom pk.

rest_framework/serializers.py

@@ -1167,7 +1167,7 @@ def build_relational_field(self, field_name, relation_info):
         field_kwargs = get_relation_kwargs(field_name, relation_info)
 
         to_field = field_kwargs.pop('to_field', None)
-        if to_field and not relation_info.related_model._meta.get_field(to_field).primary_key:
+        if to_field and not relation_info.reverse and not relation_info.related_model._meta.get_field(to_field).primary_key:
             field_kwargs['slug_field'] = to_field
             field_class = self.serializer_related_to_field
 

rest_framework/utils/field_mapping.py

@@ -238,7 +238,7 @@ def get_relation_kwargs(field_name, relation_info):
     """
     Creates a default instance of a flat relational field.
     """
-    model_field, related_model, to_many, to_field, has_through_model = relation_info
+    model_field, related_model, to_many, to_field, has_through_model, reverse = relation_info
     kwargs = {
         'queryset': related_model._default_manager,
         'view_name': get_detail_view_name(related_model)

rest_framework/utils/model_meta.py

@@ -23,7 +23,8 @@
     'related_model',
     'to_many',
     'to_field',
-    'has_through_model'
+    'has_through_model',
+    'reverse'
 ])
 
 
@@ -81,7 +82,8 @@ def _get_forward_relationships(opts):
             related_model=get_related_model(field),
             to_many=False,
             to_field=_get_to_field(field),
-            has_through_model=False
+            has_through_model=False,
+            reverse=False
         )
 
     # Deal with forward many-to-many relationships.
@@ -94,7 +96,8 @@ def _get_forward_relationships(opts):
             to_field=None,
             has_through_model=(
                 not get_remote_field(field).through._meta.auto_created
-            )
+            ),
+            reverse=False
         )
 
     return forward_relations
@@ -118,7 +121,8 @@ def _get_reverse_relationships(opts):
             related_model=related,
             to_many=get_remote_field(relation.field).multiple,
             to_field=_get_to_field(relation.field),
-            has_through_model=False
+            has_through_model=False,
+            reverse=True
         )
 
     # Deal with reverse many-to-many relationships.
@@ -135,7 +139,8 @@ def _get_reverse_relationships(opts):
             has_through_model=(
                 (getattr(get_remote_field(relation.field), 'through', None) is not None) and
                 not get_remote_field(relation.field).through._meta.auto_created
-            )
+            ),
+            reverse=True
         )
 
     return reverse_relations

tests/test_model_serializer.py

@@ -89,6 +89,15 @@ class ChoicesModel(models.Model):
     choices_field_with_nonstandard_args = models.DecimalField(max_digits=3, decimal_places=1, choices=DECIMAL_CHOICES, verbose_name='A label')
 
 
+class Issue3674ParentModel(models.Model):
+    title = models.CharField(max_length=64)
+
+
+class Issue3674ChildModel(models.Model):
+    parent = models.ForeignKey(Issue3674ParentModel, related_name='children')
+    value = models.CharField(primary_key=True, max_length=64)
+
+
 class TestModelSerializer(TestCase):
     def test_create_method(self):
         class TestSerializer(serializers.ModelSerializer):
@@ -996,3 +1005,62 @@ class Meta:
         fields = TestSerializer().fields
         self.assertFalse(fields['field_1'].required)
         self.assertTrue(fields['field_2'].required)
+
+
+class Issue3674Test(TestCase):
+    def test_nonPK_foreignkey_model_serializer(self):
+        class TestParentModel(models.Model):
+            title = models.CharField(max_length=64)
+
+        class TestChildModel(models.Model):
+            parent = models.ForeignKey(TestParentModel, related_name='children')
+            value = models.CharField(primary_key=True, max_length=64)
+
+        class TestChildModelSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = TestChildModel
+                fields = ('value', 'parent')
+
+        class TestParentModelSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = TestParentModel
+                fields = ('id', 'title', 'children')
+
+        parent_expected = dedent("""
+            TestParentModelSerializer():
+                id = IntegerField(label='ID', read_only=True)
+                title = CharField(max_length=64)
+                children = PrimaryKeyRelatedField(many=True, queryset=TestChildModel.objects.all())
+        """)
+        self.assertEqual(unicode_repr(TestParentModelSerializer()), parent_expected)
+
+        child_expected = dedent("""
+            TestChildModelSerializer():
+                value = CharField(max_length=64, validators=[<UniqueValidator(queryset=TestChildModel.objects.all())>])
+                parent = PrimaryKeyRelatedField(queryset=TestParentModel.objects.all())
+        """)
+        self.assertEqual(unicode_repr(TestChildModelSerializer()), child_expected)
+
+    def test_nonID_PK_foreignkey_model_serializer(self):
+
+        class TestChildModelSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = Issue3674ChildModel
+                fields = ('value', 'parent')
+
+        class TestParentModelSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = Issue3674ParentModel
+                fields = ('id', 'title', 'children')
+
+        parent = Issue3674ParentModel.objects.create(title='abc')
+        child = Issue3674ChildModel.objects.create(value='def', parent=parent)
+
+        parent_serializer = TestParentModelSerializer(parent)
+        child_serializer = TestChildModelSerializer(child)
+
+        parent_expected = {'children': ['def'], 'id': 1, 'title': 'abc'}
+        self.assertEqual(parent_serializer.data, parent_expected)
+
+        child_expected = {'parent': 1, 'value': 'def'}
+        self.assertEqual(child_serializer.data, child_expected)