Merge pull request #893 from tfranzel/improve_slugrelatedfield

Treat SlugRelatedField analog to PrimaryKeyRelatedField #854

drf_spectacular/openapi.py

@@ -659,11 +659,13 @@ def _map_serializer_field(self, field, direction, bypass_extensions=False):
             schema.pop('readOnly', None)
             return append_meta(build_array_type(schema), meta)
 
-        if isinstance(field, serializers.PrimaryKeyRelatedField):
+        if isinstance(field, (serializers.PrimaryKeyRelatedField, serializers.SlugRelatedField)):
+            # SlugRelatedField is essentially a non-pk version of PrimaryKeyRelatedField.
+            is_slug = isinstance(field, serializers.SlugRelatedField)
             # read_only fields do not have a Manager by design. go around and get field
             # from parent. also avoid calling Manager. __bool__ as it might be customized
             # to hit the database.
-            if getattr(field, 'queryset', None) is not None:
+            if getattr(field, 'queryset', None) is not None and not is_slug:
                 model_field = field.queryset.model._meta.pk
             else:
                 if isinstance(field.parent, serializers.ManyRelatedField):
@@ -674,14 +676,17 @@ def _map_serializer_field(self, field, direction, bypass_extensions=False):
                     source = field.source.split('.')
                 else:
                     warn(
-                        f'Could not derive type for under-specified PrimaryKeyRelatedField '
+                        f'Could not derive type for under-specified {field.__class__.__name__} '
                         f'"{field.field_name}". The serializer has no associated model (Meta class) '
                         f'and this particular field has no type without a model association. Consider '
                         f'changing the field or adding a Meta class. defaulting to string.'
                     )
                     return append_meta(build_basic_type(OpenApiTypes.STR), meta)
 
-                # estimates the relating model field and jumps to it's target model PK field.
+                if is_slug:
+                    source.append(field.slug_field)
+
+                # estimates the relating model field and jumps to its target model PK field.
                 # also differentiate as source can be direct (pk) or relation field (model).
                 model_field = follow_field_source(model, source)
                 if callable(model_field):
@@ -697,9 +702,6 @@ def _map_serializer_field(self, field, direction, bypass_extensions=False):
         if isinstance(field, serializers.StringRelatedField):
             return append_meta(build_basic_type(OpenApiTypes.STR), meta)
 
-        if isinstance(field, serializers.SlugRelatedField):
-            return append_meta(build_basic_type(OpenApiTypes.STR), meta)
-
         if isinstance(field, serializers.HyperlinkedIdentityField):
             return append_meta(build_basic_type(OpenApiTypes.URI), meta)
 

tests/test_fields.py

@@ -35,6 +35,7 @@
 class Aux(models.Model):
     id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
     field_foreign = models.ForeignKey('Aux', null=True, on_delete=models.CASCADE)
+    url = models.URLField(unique=True)
 
 
 class AuxSerializer(serializers.ModelSerializer):
@@ -191,7 +192,10 @@ def get_field_method_object(self, obj) -> dict:
 
     # extra related fields
     field_related_slug = serializers.SlugRelatedField(
-        read_only=True, source='field_foreign', slug_field='id'
+        read_only=True, source='field_foreign', slug_field='url',
+    )  # type: ignore
+    field_related_slug_many = serializers.SlugRelatedField(
+        many=True, read_only=True, source='field_m2m', slug_field='url',
     )  # type: ignore
     field_related_string = serializers.StringRelatedField(
         source='field_foreign'
@@ -292,7 +296,10 @@ def test_fields(no_warnings):
 @pytest.mark.urls(__name__)
 @pytest.mark.django_db
 def test_model_setup_is_valid():
-    aux = Aux(id='0ac6930d-87f4-40e8-8242-10a3ed31a335')
+    aux = Aux(
+        id='0ac6930d-87f4-40e8-8242-10a3ed31a335',
+        url='https://xkcd.com'
+    )
     aux.save()
 
     m = AllFields(

tests/test_fields.yml

@@ -126,6 +126,13 @@ components:
             $ref: '#/components/schemas/Aux'
         field_related_slug:
           type: string
+          format: uri
+          readOnly: true
+        field_related_slug_many:
+          type: array
+          items:
+            type: string
+            format: uri
           readOnly: true
         field_related_string:
           type: string
@@ -331,6 +338,7 @@ components:
       - field_regex
       - field_related_hyperlink
       - field_related_slug
+      - field_related_slug_many
       - field_related_string
       - field_slug
       - field_smallint
@@ -357,12 +365,17 @@ components:
           type: string
           format: uuid
           readOnly: true
+        url:
+          type: string
+          format: uri
+          maxLength: 200
         field_foreign:
           type: string
           format: uuid
           nullable: true
       required:
       - id
+      - url
   securitySchemes:
     basicAuth:
       type: http

tests/test_fields_response.json

@@ -14,10 +14,14 @@
   "field_list_serializer": [
     {
       "id": "0ac6930d-87f4-40e8-8242-10a3ed31a335",
+      "url": "https://xkcd.com",
       "field_foreign": null
     }
   ],
-  "field_related_slug": "0ac6930d-87f4-40e8-8242-10a3ed31a335",
+  "field_related_slug": "https://xkcd.com",
+  "field_related_slug_many": [
+      "https://xkcd.com"
+  ],
   "field_related_string": "Aux object (0ac6930d-87f4-40e8-8242-10a3ed31a335)",
   "field_related_hyperlink": "http://testserver/aux/0ac6930d-87f4-40e8-8242-10a3ed31a335/",
   "field_identity_hyperlink": "http://testserver/allfields/1/",