Add support for pagination in OpenAPI response schemas (#6867)

Refs #6846

This provides a way for pagination classes to add pagination properties (`count`, `next`, `results` etc.) to OpenAPI response schemas.

A new method `get_paginated_response_schema()` has been added to `BasePagination`. This method is intended to mirror `get_paginated_response()` (which takes a `list` and wraps it in a `dict`). 

Hence, `get_paginated_response_schema()` takes an unpaginated response schema (of type `array`) and wraps that with a schema object of type `object` containing the relevant properties that the pagination class adds to responses.

The default implementation of `BasePagination.get_paginated_response_schema()` simply passes the schema through unmodified, for backwards compatibility.

rest_framework/pagination.py

@@ -138,6 +138,9 @@ class BasePagination:
     def get_paginated_response(self, data):  # pragma: no cover
         raise NotImplementedError('get_paginated_response() must be implemented.')
 
+    def get_paginated_response_schema(self, schema):
+        return schema
+
     def to_html(self):  # pragma: no cover
         raise NotImplementedError('to_html() must be implemented to display page controls.')
 
@@ -222,6 +225,26 @@ class PageNumberPagination(BasePagination):
             ('results', data)
         ]))
 
+    def get_paginated_response_schema(self, schema):
+        return {
+            'type': 'object',
+            'properties': {
+                'count': {
+                    'type': 'integer',
+                    'example': 123,
+                },
+                'next': {
+                    'type': 'string',
+                    'nullable': True,
+                },
+                'previous': {
+                    'type': 'string',
+                    'nullable': True,
+                },
+                'results': schema,
+            },
+        }
+
     def get_page_size(self, request):
         if self.page_size_query_param:
             try:
@@ -369,6 +392,26 @@ class LimitOffsetPagination(BasePagination):
             ('results', data)
         ]))
 
+    def get_paginated_response_schema(self, schema):
+        return {
+            'type': 'object',
+            'properties': {
+                'count': {
+                    'type': 'integer',
+                    'example': 123,
+                },
+                'next': {
+                    'type': 'string',
+                    'nullable': True,
+                },
+                'previous': {
+                    'type': 'string',
+                    'nullable': True,
+                },
+                'results': schema,
+            },
+        }
+
     def get_limit(self, request):
         if self.limit_query_param:
             try:
@@ -840,6 +883,22 @@ class CursorPagination(BasePagination):
             ('results', data)
         ]))
 
+    def get_paginated_response_schema(self, schema):
+        return {
+            'type': 'object',
+            'properties': {
+                'next': {
+                    'type': 'string',
+                    'nullable': True,
+                },
+                'previous': {
+                    'type': 'string',
+                    'nullable': True,
+                },
+                'results': schema,
+            },
+        }
+
     def get_html_context(self):
         return {
             'previous_url': self.get_previous_link(),

rest_framework/schemas/openapi.py

@@ -206,11 +206,10 @@ class AutoSchema(ViewInspector):
         if not is_list_view(path, method, view):
             return []
 
-        pagination = getattr(view, 'pagination_class', None)
+        paginator = self._get_pagninator()
-        if not pagination:
+        if not paginator:
             return []
 
-        paginator = view.pagination_class()
         return paginator.get_schema_operation_parameters(view)
 
     def _map_field(self, field):
@@ -423,6 +422,13 @@ class AutoSchema(ViewInspector):
                     schema['maximum'] = int(digits * '9') + 1
                     schema['minimum'] = -schema['maximum']
 
+    def _get_pagninator(self):
+        pagination_class = getattr(self.view, 'pagination_class', None)
+        if pagination_class:
+            return pagination_class()
+
+        return None
+
     def _get_serializer(self, method, path):
         view = self.view
 
@@ -489,6 +495,9 @@ class AutoSchema(ViewInspector):
                 'type': 'array',
                 'items': item_schema,
             }
+            paginator = self._get_pagninator()
+            if paginator:
+                response_schema = paginator.get_paginated_response_schema(response_schema)
         else:
             response_schema = item_schema
 

tests/schemas/test_openapi.py

@@ -264,6 +264,58 @@ class TestOperationIntrospection(TestCase):
             },
         }
 
+    def test_paginated_list_response_body_generation(self):
+        """Test that pagination properties are added for a paginated list view."""
+        path = '/'
+        method = 'GET'
+
+        class Pagination(pagination.BasePagination):
+            def get_paginated_response_schema(self, schema):
+                return {
+                    'type': 'object',
+                    'item': schema,
+                }
+
+        class ItemSerializer(serializers.Serializer):
+            text = serializers.CharField()
+
+        class View(generics.GenericAPIView):
+            serializer_class = ItemSerializer
+            pagination_class = Pagination
+
+        view = create_view(
+            View,
+            method,
+            create_request(path),
+        )
+        inspector = AutoSchema()
+        inspector.view = view
+
+        responses = inspector._get_responses(path, method)
+        assert responses == {
+            '200': {
+                'description': '',
+                'content': {
+                    'application/json': {
+                        'schema': {
+                            'type': 'object',
+                            'item': {
+                                'type': 'array',
+                                'items': {
+                                    'properties': {
+                                        'text': {
+                                            'type': 'string',
+                                        },
+                                    },
+                                    'required': ['text'],
+                                },
+                            },
+                        },
+                    },
+                },
+            },
+        }
+
     def test_delete_response_body_generation(self):
         """Test that a view's delete method generates a proper response body schema."""
         path = '/{id}/'
@@ -288,15 +340,27 @@ class TestOperationIntrospection(TestCase):
         }
 
     def test_retrieve_response_body_generation(self):
-        """Test that a list of properties is returned for retrieve item views."""
+        """
+        Test that a list of properties is returned for retrieve item views.
+
+        Pagination properties should not be added as the view represents a single item.
+        """
         path = '/{id}/'
         method = 'GET'
 
+        class Pagination(pagination.BasePagination):
+            def get_paginated_response_schema(self, schema):
+                return {
+                    'type': 'object',
+                    'item': schema,
+                }
+
         class ItemSerializer(serializers.Serializer):
             text = serializers.CharField()
 
         class View(generics.GenericAPIView):
             serializer_class = ItemSerializer
+            pagination_class = Pagination
 
         view = create_view(
             View,

tests/test_pagination.py

@@ -259,6 +259,37 @@ class TestPageNumberPagination:
         with pytest.raises(exceptions.NotFound):
             self.paginate_queryset(request)
 
+    def test_get_paginated_response_schema(self):
+        unpaginated_schema = {
+            'type': 'object',
+            'item': {
+                'properties': {
+                    'test-property': {
+                        'type': 'integer',
+                    },
+                },
+            },
+        }
+
+        assert self.pagination.get_paginated_response_schema(unpaginated_schema) == {
+            'type': 'object',
+            'properties': {
+                'count': {
+                    'type': 'integer',
+                    'example': 123,
+                },
+                'next': {
+                    'type': 'string',
+                    'nullable': True,
+                },
+                'previous': {
+                    'type': 'string',
+                    'nullable': True,
+                },
+                'results': unpaginated_schema,
+            },
+        }
+
 
 class TestPageNumberPaginationOverride:
     """
@@ -535,6 +566,37 @@ class TestLimitOffset:
         assert content.get('next') == next_url
         assert content.get('previous') == prev_url
 
+    def test_get_paginated_response_schema(self):
+        unpaginated_schema = {
+            'type': 'object',
+            'item': {
+                'properties': {
+                    'test-property': {
+                        'type': 'integer',
+                    },
+                },
+            },
+        }
+
+        assert self.pagination.get_paginated_response_schema(unpaginated_schema) == {
+            'type': 'object',
+            'properties': {
+                'count': {
+                    'type': 'integer',
+                    'example': 123,
+                },
+                'next': {
+                    'type': 'string',
+                    'nullable': True,
+                },
+                'previous': {
+                    'type': 'string',
+                    'nullable': True,
+                },
+                'results': unpaginated_schema,
+            },
+        }
+
 
 class CursorPaginationTestsMixin:
 
@@ -834,6 +896,33 @@ class CursorPaginationTestsMixin:
         assert current == [1, 1, 1, 1, 1]
         assert next == [1, 2, 3, 4, 4]
 
+    def test_get_paginated_response_schema(self):
+        unpaginated_schema = {
+            'type': 'object',
+            'item': {
+                'properties': {
+                    'test-property': {
+                        'type': 'integer',
+                    },
+                },
+            },
+        }
+
+        assert self.pagination.get_paginated_response_schema(unpaginated_schema) == {
+            'type': 'object',
+            'properties': {
+                'next': {
+                    'type': 'string',
+                    'nullable': True,
+                },
+                'previous': {
+                    'type': 'string',
+                    'nullable': True,
+                },
+                'results': unpaginated_schema,
+            },
+        }
+
 
 class TestCursorPagination(CursorPaginationTestsMixin):
     """