Merge pull request #899 from tfranzel/fix_slugrelated

utilize queryset for SlugRelatedField #897

Author: tfranzel

drf_spectacular/openapi.py

@@ -666,8 +666,13 @@ def _map_serializer_field(self, field, direction, bypass_extensions=False):
             # 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 and not is_slug:
-                model_field = field.queryset.model._meta.pk
+            if getattr(field, 'queryset', None) is not None:
+                if is_slug:
+                    model = field.queryset.model
+                    source = [field.slug_field]
+                    model_field = follow_field_source(model, source, default=models.TextField())
+                else:
+                    model_field = field.queryset.model._meta.pk
             else:
                 if isinstance(field.parent, serializers.ManyRelatedField):
                     model = field.parent.parent.Meta.model
@@ -689,10 +694,8 @@ def _map_serializer_field(self, field, direction, bypass_extensions=False):
 
                 # 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):
-                    # follow_field_source bailed with a warning. be graceful and default to str.
-                    model_field = models.TextField()
+                # be graceful and default to string.
+                model_field = follow_field_source(model, source, default=models.TextField())
 
             # primary keys are usually non-editable (readOnly=True) and map_model_field correctly
             # signals that attribute. however this does not apply in the context of relations.

drf_spectacular/plumbing.py

@@ -572,7 +572,7 @@ def _follow_return_type(a_callable):
     return target_type
 
 
-def follow_field_source(model, path, emit_warnings=True):
+def follow_field_source(model, path, default=None, emit_warnings=True):
     """
     a model traversal chain "foreignkey.foreignkey.value" can either end with an actual model field
     instance "value" or a model property function named "value". differentiate the cases.
@@ -594,7 +594,7 @@ def follow_field_source(model, path, emit_warnings=True):
 
     def dummy_property(obj) -> str:  # type: ignore
         pass  # pragma: no cover
-    return dummy_property
+    return default or dummy_property
 
 
 def follow_model_field_lookup(model, lookup):

tests/test_fields.py

@@ -194,6 +194,9 @@ def get_field_method_object(self, obj) -> dict:
     field_related_slug = serializers.SlugRelatedField(
         read_only=True, source='field_foreign', slug_field='url',
     )  # type: ignore
+    field_related_slug_queryset = serializers.SlugRelatedField(
+        source='field_foreign', slug_field='url', queryset=Aux.objects.all()
+    )  # type: ignore
     field_related_slug_many = serializers.SlugRelatedField(
         many=True, read_only=True, source='field_m2m', slug_field='url',
     )  # type: ignore

tests/test_fields.yml

@@ -129,6 +129,10 @@ components:
           format: uri
           description: URL identifier for Aux
           readOnly: true
+        field_related_slug_queryset:
+          type: string
+          format: uri
+          description: URL identifier for Aux
         field_related_slug_many:
           type: array
           items:
@@ -341,6 +345,7 @@ components:
       - field_related_hyperlink
       - field_related_slug
       - field_related_slug_many
+      - field_related_slug_queryset
       - field_related_string
       - field_slug
       - field_smallint

tests/test_fields_response.json

@@ -19,6 +19,7 @@
     }
   ],
   "field_related_slug": "https://xkcd.com",
+  "field_related_slug_queryset": "https://xkcd.com",
   "field_related_slug_many": [
       "https://xkcd.com"
   ],