handle default value for SerializerMethodField #422

drf_spectacular/openapi.py

@@ -766,9 +766,10 @@ def _get_serializer_field_meta(self, field):
         if field.allow_null:
             meta['nullable'] = True
         if field.default is not None and field.default != empty and not callable(field.default):
-            if isinstance(field, serializers.ModelField):
-                # Skip coercion for lack of a better solution. ModelField.to_representation() is special
-                # in that it requires a model instance (which we don't have) instead of a plain value.
+            if isinstance(field, (serializers.ModelField, serializers.SerializerMethodField)):
+                # Skip coercion for lack of a better solution. ModelField.to_representation()
+                # and SerializerMethodField.to_representation() are special in that they require
+                # a model instance or object (which we don't have) instead of a plain value.
                 default = field.default
             else:
                 default = field.to_representation(field.default)

tests/test_regressions.py

@@ -2240,7 +2240,7 @@ def view_func(request, format=None):
     }
 
 
-def test_serializer_modelfield_with_default_value(no_warnings):
+def test_serializer_modelfield_and_methodfield_with_default_value(no_warnings):
     class M8Model(models.Model):
         field = models.IntegerField()
 
@@ -2249,6 +2249,10 @@ class XSerializer(serializers.ModelSerializer):
             model_field=M8Model()._meta.get_field('field'),
             default=3
         )
+        field_smf = serializers.SerializerMethodField(default=4)
+
+        def get_field_smf(self, obj) -> int:
+            return 0  # pragma: no cover
 
         class Meta:
             model = M8Model
@@ -2262,6 +2266,9 @@ class XViewset(viewsets.ModelViewSet):
     assert schema['components']['schemas']['X']['properties']['field'] == {
         'type': 'integer', 'default': 3
     }
+    assert schema['components']['schemas']['X']['properties']['field_smf'] == {
+        'type': 'integer', 'readOnly': True, 'default': 4
+    }
 
 
 def test_literal_dot_in_regex_path(no_warnings):