Extract method for manual_fields processing (#5633)

* Extract method for `manual_fields` processing

Allows reuse of logic to replace Field instances in a field list by `Field.name`.

Adds a utility function for the logic plus a wrapper method on `AutoSchema`.

Closes #5632

* Manual fields suggestions (#2)

* Use OrderedDict in inspectors

* Move empty check to 'update_fields()'

* Make 'update_fields()' an AutoSchema staticmethod

* Add 'AutoSchema.get_manual_fields()'

* Conform '.get_manual_fields()' to other methods

* Add test for update_fields

* Make sure `manual_fields` is a list.

(As documented to be)

* Add docs for new AutoSchema methods.

* `get_manual_fields`
* `update_fields`

* Add release notes for PR.

docs/api-guide/schemas.md

@@ -603,6 +603,31 @@ Return a list of `coreapi.Link()` instances, as returned by the `get_schema_fiel
 
 Return a list of `coreapi.Link()` instances, as returned by the `get_schema_fields()` method of any filter classes used by the view.
 
+### get_manual_fields(self, path, method)
+
+Return a list of `coreapi.Field()` instances to be added to or replace generated fields. Defaults to (optional) `manual_fields` passed to `AutoSchema` constructor.
+
+May be overridden to customise manual fields by `path` or `method`. For example, a per-method adjustment may look like this:
+
+```python
+def get_manual_fields(self, path, method):
+    """Example adding per-method fields."""
+
+    extra_fields = []
+    if method=='GET':
+        extra_fields = # ... list of extra fields for GET ...
+    if method=='POST':
+        extra_fields = # ... list of extra fields for POST ...
+
+    manual_fields = super().get_manual_fields()
+    return manual_fields + extra_fields
+```
+
+### update_fields(fields, update_with)
+
+Utility `staticmethod`. Encapsulates logic to add or replace fields from a list
+by `Field.name`. May be overridden to adjust replacement criteria.
+
 
 ## ManualSchema
 

docs/topics/release-notes.md

@@ -40,6 +40,25 @@ You can determine your currently installed version using `pip freeze`:
 
 ## 3.7.x series
 
+### 3.7.4
+
+**Date**: UNRELEASED
+
+* Extract method for `manual_fields` processing [#5633][gh5633]
+
+    Allows for easier customisation of `manual_fields` processing, for example
+    to provide per-method manual fields. `AutoSchema` adds `get_manual_fields`,
+    as the intended override point, and a utility method `update_fields`, to
+    handle by-name field replacement from a list, which, in general, you are not
+    expected to override.
+
+    Note: `AutoSchema.__init__` now ensures `manual_fields` is a list.
+    Previously may have been stored internally as `None`.
+
+
+[gh5633]: https://github.com/encode/django-rest-framework/issues/5633
+
+
 
 ### 3.7.3
 

rest_framework/schemas/inspectors.py

@@ -172,7 +172,8 @@ class AutoSchema(ViewInspector):
         * `manual_fields`: list of `coreapi.Field` instances that
             will be added to auto-generated fields, overwriting on `Field.name`
         """
-
+        if manual_fields is None:
+            manual_fields = []
         self._manual_fields = manual_fields
 
     def get_link(self, path, method, base_url):
@@ -181,11 +182,8 @@ class AutoSchema(ViewInspector):
         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())
+        manual_fields = self.get_manual_fields(path, method)
+        fields = self.update_fields(fields, manual_fields)
 
         if fields and any([field.location in ('form', 'body') for field in fields]):
             encoding = self.get_encoding(path, method)
@@ -379,6 +377,31 @@ class AutoSchema(ViewInspector):
             fields += filter_backend().get_schema_fields(self.view)
         return fields
 
+    def get_manual_fields(self, path, method):
+        return self._manual_fields
+
+    @staticmethod
+    def update_fields(fields, update_with):
+        """
+        Update list of coreapi.Field instances, overwriting on `Field.name`.
+
+        Utility function to handle replacing coreapi.Field fields
+        from a list by name. Used to handle `manual_fields`.
+
+        Parameters:
+
+        * `fields`: list of `coreapi.Field` instances to update
+        * `update_with: list of `coreapi.Field` instances to add or replace.
+        """
+        if not update_with:
+            return fields
+
+        by_name = OrderedDict((f.name, f) for f in fields)
+        for f in update_with:
+            by_name[f.name] = f
+        fields = list(by_name.values())
+        return fields
+
     def get_encoding(self, path, method):
         """
         Return the 'encoding' parameter to use for a given endpoint.

tests/test_schemas.py

@@ -516,7 +516,7 @@ class Test4605Regression(TestCase):
         assert prefix == '/'
 
 
-class TestDescriptor(TestCase):
+class TestAutoSchema(TestCase):
 
     def test_apiview_schema_descriptor(self):
         view = APIView()
@@ -528,7 +528,43 @@ class TestDescriptor(TestCase):
         with pytest.raises(AssertionError):
             descriptor.get_link(None, None, None)  # ???: Do the dummy arguments require a tighter assert?
 
-    def test_manual_fields(self):
+    def test_update_fields(self):
+        """
+        That updating fields by-name helper is correct
+
+        Recall: `update_fields(fields, update_with)`
+        """
+        schema = AutoSchema()
+        fields = []
+
+        # Adds a field...
+        fields = schema.update_fields(fields, [
+            coreapi.Field(
+                "my_field",
+                required=True,
+                location="path",
+                schema=coreschema.String()
+            ),
+        ])
+
+        assert len(fields) == 1
+        assert fields[0].name == "my_field"
+
+        # Replaces a field...
+        fields = schema.update_fields(fields, [
+            coreapi.Field(
+                "my_field",
+                required=False,
+                location="path",
+                schema=coreschema.String()
+            ),
+        ])
+
+        assert len(fields) == 1
+        assert fields[0].required is False
+
+    def test_get_manual_fields(self):
+        """That get_manual_fields is applied during get_link"""
 
         class CustomView(APIView):
             schema = AutoSchema(manual_fields=[