add @requires support

README.md

@@ -27,9 +27,9 @@ Supports now:
     ```
 * extend  # extend remote types
 * external  # mark field as external 
+* requires  # mark that field resolver requires other fields to be pre-fetched
 
 Todo implement:
-* @requires
 * @provides
 
 

graphene_federation/__init__.py

@@ -1,2 +1,2 @@
 from .main import key, build_schema
-from .extend import extend, external
+from .extend import extend, external, requires

graphene_federation/extend.py

@@ -20,3 +20,8 @@ def decorator(Type):
 def external(field):
     field._external = True
     return field
+
+
+def requires(field, fields: str):
+    field._requires = fields
+    return field

graphene_federation/service.py

@@ -7,20 +7,36 @@
 from .entity import custom_entities
 
 
-def _mark_external(entity_name, entity, schema, auto_camelcase):
+def _mark_field(
+        entity_name, entity, schema: str, mark_attr_name: str,
+        decorator_resolver: callable, auto_camelcase: bool
+):
     for field_name in dir(entity):
         field = getattr(entity, field_name, None)
-        if field is not None and getattr(field, '_external', False):
+        if field is not None and getattr(field, mark_attr_name, None):
             # todo write tests on regexp
             schema_field_name = to_camel_case(field_name) if auto_camelcase else field_name
             pattern = re.compile(
                 r"(\s%s\s[^\{]*\{[^\}]*\s%s[\s]*:[\s]*[^\s]+)(\s)" % (
                     entity_name, schema_field_name))
-            schema = pattern.sub(r'\g<1> @external ', schema)
+            schema = pattern.sub(
+                rf'\g<1> {decorator_resolver(getattr(field, mark_attr_name))} ', schema)
 
     return schema
 
 
+def _mark_external(entity_name, entity, schema, auto_camelcase):
+    return _mark_field(
+        entity_name, entity, schema, '_external', lambda _: '@external', auto_camelcase)
+
+
+def _mark_requires(entity_name, entity, schema, auto_camelcase):
+    return _mark_field(
+        entity_name, entity, schema, '_requires', lambda fields: f'@requires(fields: "{fields}")',
+        auto_camelcase
+    )
+
+
 def get_sdl(schema, custom_entities):
     string_schema = str(schema)
     string_schema = string_schema.replace("\n", " ")
@@ -37,6 +53,7 @@ def get_sdl(schema, custom_entities):
 
     for entity_name, entity in extended_types.items():
         string_schema = _mark_external(entity_name, entity, string_schema, schema.auto_camelcase)
+        string_schema = _mark_requires(entity_name, entity, string_schema, schema.auto_camelcase)
 
         type_def_re = r"type %s ([^\{]*)" % entity_name
         type_def = r"type %s " % entity_name

integration_tests/service_c/src/schema.py

@@ -1,10 +1,15 @@
 from graphene import ObjectType, String, Int, List, NonNull, Field
-from graphene_federation import build_schema, extend, external
+from graphene_federation import build_schema, extend, external, requires
 
 
 @extend(fields='id')
 class User(ObjectType):
     id = external(Int(required=True))
+    primary_email = external(String())
+    uppercase_email = requires(String(), fields='primaryEmail')
+
+    def resolve_uppercase_email(self, info):
+        return self.primary_email.upper() if self.primary_email else self.primary_email
 
 
 class Article(ObjectType):

integration_tests/tests/tests/test_main.py

@@ -118,3 +118,30 @@ def test_multiple_key_decorators_apply_multiple_key_annotations():
 def test_avoid_duplication_of_key_decorator():
     sdl = fetch_sdl('service_a')
     assert 'extend type FileNode   @key(fields: \"id\") {' in sdl
+
+
+def test_requires():
+    query = {
+        'query': """
+            query {
+                articles {
+                    id
+                    text
+                    author {
+                        uppercaseEmail
+                    }
+                }
+            }
+        """,
+        'variables': {}
+    }
+    response = requests.post(
+        'http://federation:3000/graphql/',
+        json=query,
+    )
+    assert response.status_code == 200
+    data = json.loads(response.content)['data']
+    articles = data['articles']
+
+    assert articles == [
+        {'id': 1, 'text': 'some text', 'author': {'uppercaseEmail': 'NAME_5@GMAIL.COM'}}]