Respect serializer's id field.

example/tests/unit/test_renderer_class_methods.py

@@ -41,6 +41,40 @@ def test_build_json_resource_obj():
         serializer.fields, resource, resource_instance, 'user') == output
 
 
+class PrefixedId(serializers.CharField):
+    def get_attribute(self, instance):
+        return 'my-id-' + str(instance.id)
+
+    def to_internal_value(self, data):
+        return int(data['id'].split('-')[-1])
+
+
+class ResourceWithIdSerializer(serializers.ModelSerializer):
+    id = PrefixedId(required=False)
+
+    class Meta:
+        fields = ('id', 'username',)
+        model = get_user_model()
+
+
+def test_build_json_resource_obj_respects_serializer_id():
+    serializer = ResourceWithIdSerializer(data={'username': 'Alice'})
+    serializer.is_valid()
+    resource_instance = serializer.save()
+    resource = serializer.data
+
+    output = {
+        'type': 'user',
+        'id': 'my-id-1',
+        'attributes': {
+            'username': 'Alice'
+        },
+    }
+
+    assert JSONRenderer.build_json_resource_obj(
+        serializer.fields, resource, resource_instance, 'user') == output
+
+
 def test_can_override_methods():
     """
     Make sure extract_attributes and extract_relationships can be overriden.

rest_framework_json_api/renderers.py

@@ -487,9 +487,16 @@ def build_json_resource_obj(cls, fields, resource, resource_instance, resource_n
         # Determine type from the instance if the underlying model is polymorphic
         if force_type_resolution:
             resource_name = utils.get_resource_type_from_instance(resource_instance)
+
+        # Allow serializer `id` field to override model pk
+        if 'id' in resource:
+            resource_id = encoding.force_text(resource['id'])
+        else:
+            resource_id = encoding.force_text(resource_instance.pk) if resource_instance else None
+
         resource_data = [
             ('type', resource_name),
-            ('id', encoding.force_text(resource_instance.pk) if resource_instance else None),
+            ('id', resource_id),
             ('attributes', cls.extract_attributes(fields, resource)),
         ]
         relationships = cls.extract_relationships(fields, resource, resource_instance)