Implement 'R.<type>.CanBe` decorator.

Author: jhgg

epoxy/metaclasses/object_type.py

@@ -36,7 +36,7 @@ def __new__(mcs, name, bases, attrs):
         return cls
 
     @staticmethod
-    def _register(object_type):
+    def _register(object_type, cls):
         raise NotImplementedError('_register must be implemented in the sub-metaclass')
 
     @staticmethod

epoxy/registry.py

@@ -47,6 +47,7 @@ def __init__(self):
         self._added_impl_types = set()
         self._interface_declared_fields = {}
         self._registered_types_can_be = defaultdict(set)
+        self._pending_types_can_be = defaultdict(set)
         self.ObjectType = self._create_object_type_class()
         self.Implements = ClassTypeCreator(self, self._create_object_type_class)
         self.Union = ClassTypeCreator(self, self._create_union_type_class)
@@ -185,11 +186,22 @@ def _add_interface_declared_fields(self, interface, attrs):
     def _get_interface_declared_fields(self, interface):
         return self._interface_declared_fields.get(interface, {})
 
+    def _register_possible_type_for(self, type_name, klass):
+        type = self._registered_types.get(type_name)
+        if type:
+            self._registered_types_can_be[type].add(klass)
+
+        else:
+            self._pending_types_can_be[type_name].add(klass)
+
     def _add_impl_to_interfaces(self):
         for type in self._registered_types.values():
             if not isinstance(type, GraphQLObjectType):
                 continue
 
+            if type.name in self._pending_types_can_be:
+                self._registered_types_can_be[type] |= self._pending_types_can_be.pop(type.name)
+
             if type in self._added_impl_types:
                 continue
 

epoxy/thunk.py

@@ -69,7 +69,8 @@ def __call__(self):
 
     # noinspection PyPep8Naming
     def CanBe(self, klass):
-        raise NotImplementedError('CanBe not yet implemented.')
+        self.registry._register_possible_type_for(self.item, klass)
+        return klass
 
 
 class ThunkList(object):

tests/test_can_be.py

@@ -0,0 +1,83 @@
+from graphql.core import graphql
+from epoxy import TypeRegistry
+
+
+def test_can_be():
+    R = TypeRegistry()
+
+    @R.Cat.CanBe
+    class MyCat(object):
+        def __init__(self, name, meow):
+            self.name = name
+            self.meow = meow
+
+    class Pet(R.Interface):
+        name = R.String
+
+    class Dog(R.Implements.Pet):
+        bark = R.String
+
+    class Cat(R.Implements.Pet):
+        meow = R.String
+
+    class Bird(R.Implements.Pet):
+        tweet = R.String
+
+    class Query(R.ObjectType):
+        pets = R.Pet.List
+
+    @R.Dog.CanBe
+    class MyDog(object):
+        def __init__(self, name, bark):
+            self.name = name
+            self.bark = bark
+
+    schema = R.Schema(Query)
+
+    @R.Bird.CanBe
+    class MyBird(object):
+        def __init__(self, name, tweet):
+            self.name = name
+            self.tweet = tweet
+
+    data = Query(pets=[
+        MyDog(name='Clifford', bark='Really big bark, because it\'s a really big dog.'),
+        MyCat(name='Garfield', meow='Lasagna'),
+        MyBird(name='Tweetie', tweet='#yolo'),
+
+        Dog(name='OTClifford', bark='Really big bark, because it\'s a really big dog.'),
+        Cat(name='OTGarfield', meow='Lasagna'),
+        Bird(name='OTTweetie', tweet='#yolo'),
+    ])
+
+    result = graphql(schema, '''
+        {
+            pets {
+                name
+                __typename
+                ... on Dog {
+                    bark
+                }
+
+                ... on Cat {
+                    meow
+                }
+
+                ... on Bird {
+                    tweet
+                }
+            }
+        }
+
+    ''', data)
+    assert not result.errors
+    assert result.data == {
+        'pets': [
+            {'__typename': 'Dog', 'bark': "Really big bark, because it's a really big dog.", 'name': 'Clifford'},
+            {'__typename': 'Cat', 'meow': 'Lasagna', 'name': 'Garfield'},
+            {'__typename': 'Bird', 'tweet': '#yolo', 'name': 'Tweetie'},
+            {'__typename': 'Dog', 'bark': "Really big bark, because it's a really big dog.", 'name': 'OTClifford'},
+            {'__typename': 'Cat', 'meow': 'Lasagna', 'name': 'OTGarfield'},
+            {'__typename': 'Bird', 'tweet': '#yolo', 'name': 'OTTweetie'},
+        ]
+    }