add choice field display method handling #1228

drf_spectacular/openapi.py

@@ -893,7 +893,14 @@ def _map_serializer_field(self, field, direction, bypass_extensions=False):
                 return append_meta(build_basic_type(OpenApiTypes.STR), meta)
 
             target = follow_field_source(model, source)
-            if callable(target):
+            if (
+                hasattr(target, "_partialmethod")
+                and target._partialmethod.func.__name__ == '_get_FIELD_display'
+            ):
+                # the only way to detect an uninitialized partial method
+                # this is a convenience method for model choice fields and is mostly a string
+                schema = build_basic_type(str)
+            elif callable(target):
                 schema = self._map_response_type_hint(target)
             elif isinstance(target, models.Field):
                 schema = self._map_model_field(target, direction)

tests/test_regressions.py

@@ -3385,3 +3385,28 @@ def view_func(request, format=None):
         'baz': {'type': 'integer'},
         'qux': {'items': {'type': 'integer'}, 'type': 'array'}
     }
+
+
+def test_model_choice_display_method_on_readonly(no_warnings):
+    class M15(models.Model):
+        SHIRT_SIZES = {"S": "Small", "M": "Medium", "L": "Large"}
+
+        name = models.CharField(max_length=60)
+        shirt_size = models.CharField(max_length=1, choices=SHIRT_SIZES)
+
+    class XSerializer(serializers.ModelSerializer):
+        field_name = serializers.ReadOnlyField(source='name')
+        field_shirts = serializers.ReadOnlyField(source='get_shirt_size_display')
+
+        class Meta:
+            model = M15
+            fields = '__all__'
+
+    class XViewset(viewsets.ModelViewSet):
+        queryset = M15.objects.all()
+        serializer_class = XSerializer
+
+    schema = generate_schema('x', XViewset)
+    assert schema['components']['schemas']['X']["properties"]["field_shirts"] == {
+        "readOnly": True, 'type': 'string'
+    }