refactor: make relay connections extendable

graphene/relay/connection.py

@@ -61,8 +61,9 @@ class Connection(ObjectType):
         abstract = True
 
     @classmethod
-    def __init_subclass_with_meta__(cls, node=None, name=None, **options):
-        _meta = ConnectionOptions(cls)
+    def __init_subclass_with_meta__(cls, node=None, name=None, _meta=None, **options):
+        if not _meta:
+            _meta = ConnectionOptions(cls)
         assert node, f"You have to provide a node in {cls.__name__}.Meta"
         assert isinstance(node, NonNull) or issubclass(
             node, (Scalar, Enum, ObjectType, Interface, Union, NonNull)
@@ -92,19 +93,26 @@ class Connection(ObjectType):
         cls.Edge = edge
 
         options["name"] = name
+
         _meta.node = node
-        _meta.fields = {
-            "page_info": Field(
-                PageInfo,
-                name="pageInfo",
-                required=True,
-                description="Pagination data for this connection.",
-            ),
-            "edges": Field(
-                NonNull(List(edge)),
-                description="Contains the nodes in this connection.",
-            ),
-        }
+
+        if not _meta.fields:
+            _meta.fields = {}
+
+        _meta.fields.update(
+            {
+                "page_info": Field(
+                    PageInfo,
+                    name="pageInfo",
+                    required=True,
+                    description="Pagination data for this connection.",
+                ),
+                "edges": Field(
+                    NonNull(List(edge)),
+                    description="Contains the nodes in this connection.",
+                ),
+            }
+        )
         return super(Connection, cls).__init_subclass_with_meta__(
             _meta=_meta, **options
         )

graphene/relay/tests/test_connection.py

@@ -1,7 +1,7 @@
 from pytest import raises
 
 from ...types import Argument, Field, Int, List, NonNull, ObjectType, Schema, String
-from ..connection import Connection, ConnectionField, PageInfo
+from ..connection import Connection, ConnectionField, PageInfo, ConnectionOptions
 from ..node import Node
 
 
@@ -51,6 +51,55 @@ def test_connection_inherit_abstracttype():
     assert list(fields) == ["page_info", "edges", "extra"]
 
 
+def test_connection_extra_abstract_fields():
+    class ConnectionWithNodes(Connection):
+        class Meta:
+            abstract = True
+
+        @classmethod
+        def __init_subclass_with_meta__(cls, node=None, name=None, **options):
+            _meta = ConnectionOptions(cls)
+
+            _meta.fields = {
+                "nodes": Field(
+                    NonNull(List(node)),
+                    description="Contains all the nodes in this connection.",
+                ),
+            }
+
+            return super(ConnectionWithNodes, cls).__init_subclass_with_meta__(
+                node=node, name=name, _meta=_meta, **options
+            )
+
+    class MyObjectConnection(ConnectionWithNodes):
+        class Meta:
+            node = MyObject
+
+        class Edge:
+            other = String()
+
+    assert MyObjectConnection._meta.name == "MyObjectConnection"
+    fields = MyObjectConnection._meta.fields
+    assert list(fields) == ["nodes", "page_info", "edges"]
+    edge_field = fields["edges"]
+    pageinfo_field = fields["page_info"]
+    nodes_field = fields["nodes"]
+
+    assert isinstance(edge_field, Field)
+    assert isinstance(edge_field.type, NonNull)
+    assert isinstance(edge_field.type.of_type, List)
+    assert edge_field.type.of_type.of_type == MyObjectConnection.Edge
+
+    assert isinstance(pageinfo_field, Field)
+    assert isinstance(pageinfo_field.type, NonNull)
+    assert pageinfo_field.type.of_type == PageInfo
+
+    assert isinstance(nodes_field, Field)
+    assert isinstance(nodes_field.type, NonNull)
+    assert isinstance(nodes_field.type.of_type, List)
+    assert nodes_field.type.of_type.of_type == MyObject
+
+
 def test_connection_name():
     custom_name = "MyObjectCustomNameConnection"