Add manual_fields kwarg to AutoSchema

docs/api-guide/schemas.md

@@ -164,8 +164,7 @@ appropriate Core API `Link` object for the view, request method and path:
     auto_schema = view.schema
     coreapi_link = auto_schema.get_link(...)
 
-
-(Aside: In compiling the schema, `SchemaGenerator` calls `view.schema.get_link()` for
+(In compiling the schema, `SchemaGenerator` calls `view.schema.get_link()` for
 each view, allowed method and path.)
 
 To customise the `Link` generation you may:
@@ -178,9 +177,9 @@ To customise the `Link` generation you may:
         class CustomView(APIView):
             ...
             schema = AutoSchema(
-                manual_fields= {
-                    "extra_field": coreapi.Field(...)
-                }
+                manual_fields=[
+                    coreapi.Field("extra_field", ...),
+                ]
             )
 
     This allows extension for the most common case without subclassing.
@@ -512,9 +511,22 @@ A class that deals with introspection of individual views for schema generation.
 
 `AutoSchema` is attached to `APIView` via the `schema` attribute.
 
-Typically you will subclass `AutoSchema` to customise schema generation
-and then set your subclass on your view.
+The `AutoSchema` constructor takes a single keyword argument  `manual_fields`.
+
+### `manual_fields`: a `list` of `coreapi.Field` instances that will be added to
+the generated fields. Generated fields with a matching `name` will be overwritten.
 
+    class CustomView(APIView):
+        schema = AutoSchema(manual_fields=[
+            coreapi.Field(
+                "my_extra_field",
+                required=True,
+                location="path",
+                schema=coreschema.String()
+            ),
+        ])
+
+For more advanced customisation subclass `AutoSchema` to customise schema generation.
 
     class CustomViewSchema(AutoSchema):
         """
@@ -529,10 +541,13 @@ and then set your subclass on your view.
     class MyView(APIView):
       schema = CustomViewSchema()
 
+The following methods are available to override.
+
 ### get_link(self, path, method, base_url)
 
 Returns a `coreapi.Link` instance corresponding to the given view.
 
+This is the main entry point.
 You can override this if you need to provide custom behaviors for particular views.
 
 ### get_description(self, path, method)
@@ -565,7 +580,7 @@ Return a list of `coreapi.Link()` instances, as returned by the `get_schema_fiel
 
 ## ManualSchema
 
-`APIViewSchemaDescriptor` subclass for specifying a manual schema.
+Allows specifying a manual schema for a view:
 
     class MyView(APIView):
       schema = ManualSchema(coreapi.Link(

rest_framework/schemas.py

@@ -301,12 +301,28 @@ class AutoSchema(ViewInspector):
 
     Responsible for per-view instrospection and schema generation.
     """
+    def __init__(self, manual_fields=None):
+        """
+        Parameters:
+
+        * `manual_fields`: list of `coreapi.Field` instances that
+            will be added to auto-generated fields, overwriting on `Field.name`
+        """
+
+        self._manual_fields = manual_fields
+
     def get_link(self, path, method, base_url):
         fields = self.get_path_fields(path, method)
         fields += self.get_serializer_fields(path, method)
         fields += self.get_pagination_fields(path, method)
         fields += self.get_filter_fields(path, method)
 
+        if self._manual_fields is not None:
+            by_name = {f.name: f for f in fields}
+            for f in self._manual_fields:
+                by_name[f.name] = f
+            fields = list(by_name.values())
+
         if fields and any([field.location in ('form', 'body') for field in fields]):
             encoding = self.get_encoding(path, method)
         else:

tests/test_schemas.py

@@ -513,6 +513,25 @@ def test_get_link_requires_instance(self):
         with pytest.raises(AssertionError):
             descriptor.get_link(None, None, None)  # ???: Do the dummy arguments require a tighter assert?
 
+    def test_manual_fields(self):
+
+        class CustomView(APIView):
+            schema = AutoSchema(manual_fields=[
+                coreapi.Field(
+                    "my_extra_field",
+                    required=True,
+                    location="path",
+                    schema=coreschema.String()
+                ),
+            ])
+
+        view = CustomView()
+        link = view.schema.get_link('/a/url/{id}/', 'GET', '')
+        fields = link.fields
+
+        assert len(fields) == 2
+        assert "my_extra_field" in [f.name for f in fields]
+
     def test_view_with_manual_schema(self):
 
         expected = coreapi.Link(