Add error responses to schema

rest_framework/schemas/openapi.py

@@ -185,6 +185,9 @@ class AutoSchema(ViewInspector):
 
         return component_name
 
+    def get_error_component_name(self, serializer):
+        return self.get_component_name(serializer) + 'Error'
+
     def get_components(self, path, method):
         """
         Return components with their properties from the serializer.
@@ -201,6 +204,11 @@ class AutoSchema(ViewInspector):
             content = self.map_serializer(request_serializer)
             self.components.setdefault(component_name, content)
 
+            if method.lower() in ('put', 'post', 'patch'):
+                error_component_name = self.get_error_component_name(request_serializer)
+                error_content = self.map_error_serializer(request_serializer)
+                self.components.setdefault(error_component_name, error_content)
+
         if isinstance(response_serializer, serializers.Serializer):
             component_name = self.get_component_name(response_serializer)
             content = self.map_serializer(response_serializer)
@@ -509,6 +517,23 @@ class AutoSchema(ViewInspector):
         }
         return {'type': FIELD_CLASS_SCHEMA_TYPE.get(field.__class__, 'string')}
 
+    def map_error_field(self, field):
+        if isinstance(field, serializers.ListSerializer):
+            return {
+                'type': 'array',
+                'items': self.map_error_serializer(field.child)
+            }
+        if isinstance(field, serializers.Serializer):
+            return self.map_error_serializer(field)
+        if isinstance(field, serializers.SerializerMethodField) and isinstance(field.output_field, serializers.Serializer):
+            return self.map_error_serializer(field.output_field)
+        return {
+            'type': 'array',
+            'items': {
+                'type': 'string'
+            },
+        }
+
     def _map_min_max(self, field, content):
         if field.max_value:
             content['maximum'] = field.max_value
@@ -553,6 +578,33 @@ class AutoSchema(ViewInspector):
         self.components[component_name] = result
         return self._get_reference(serializer)
 
+    def map_error_serializer(self, serializer):
+        properties = {
+            api_settings.NON_FIELD_ERRORS_KEY: {
+                'type': 'array',
+                'items': {
+                    'type': 'string'
+                }
+            }
+        }
+
+        for field in serializer.fields.values():
+            if isinstance(field, serializers.HiddenField):
+                continue
+            if field.read_only:
+                continue
+
+            properties[field.field_name] = self.map_error_field(field)
+
+        result = {
+            'type': 'object',
+            'properties': properties
+        }
+
+        component_name = self.get_error_component_name(serializer=serializer)
+        self.components[component_name] = result
+        return self._get_error_reference(serializer)
+
     def map_field_validators(self, field, schema):
         """
         map field validators
@@ -643,6 +695,9 @@ class AutoSchema(ViewInspector):
     def _get_reference(self, serializer):
         return {'$ref': '#/components/schemas/{}'.format(self.get_component_name(serializer))}
 
+    def _get_error_reference(self, serializer):
+        return {'$ref': '#/components/schemas/{}'.format(self.get_error_component_name(serializer))}
+
     def get_request_body(self, path, method):
         if method not in ('PUT', 'PATCH', 'POST'):
             return {}
@@ -691,7 +746,7 @@ class AutoSchema(ViewInspector):
         else:
             response_schema = item_schema
         status_code = '201' if method == 'POST' else '200'
-        return {
+        responses = {
             status_code: {
                 'content': {
                     ct: {'schema': response_schema}
@@ -704,6 +759,20 @@ class AutoSchema(ViewInspector):
             }
         }
 
+        if method in ('POST', 'PUT', 'PATCH'):
+            error_schema = self._get_error_reference(self.get_request_serializer(path, method))
+            responses['400'] = {
+                'content': {
+                    ct: {'schema': error_schema}
+                    for ct in self.response_media_types
+                },
+                # description is a mandatory property,
+                # https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.2.md#responseObject
+                # TODO: put something meaningful into it
+                'description': ""
+            }
+        return responses
+
     def get_tags(self, path, method):
         # If user have specified tags, use them.
         if self._tags:

tests/schemas/test_openapi.py

@@ -793,6 +793,23 @@ class TestOperationIntrospection(TestCase):
                 },
                 'required': ['text'],
                 'type': 'object'
+            },
+            'RequestError': {
+                'properties': {
+                    'non_field_errors': {
+                        'type': 'array',
+                        'items': {
+                            'type': 'string'
+                        }
+                    },
+                    'text': {
+                        'type': 'array',
+                        'items': {
+                            'type': 'string'
+                        }
+                    }
+                },
+                'type': 'object'
             }
         }
 
@@ -830,6 +847,16 @@ class TestOperationIntrospection(TestCase):
                         }
                     },
                     'description': ''
+                },
+                '400': {
+                    'content': {
+                        'application/json': {
+                            'schema': {
+                                '$ref': '#/components/schemas/RequestError'
+                            }
+                        }
+                    },
+                    'description': ''
                 }
             },
             'tags': ['']