Add support for optional connections

RELEASE.md

@@ -0,0 +1,51 @@
+Release type: minor
+
+This release adds support for making Relay connection optional, this is useful
+when you want to add permission classes to the connection and not fail the whole
+query if the user doesn't have permission to access the connection.
+
+Example:
+
+```python
+import strawberry
+from strawberry import relay
+from strawberry.permission import BasePermission
+
+
+class IsAuthenticated(BasePermission):
+    message = "User is not authenticated"
+
+    # This method can also be async!
+    def has_permission(
+        self, source: typing.Any, info: strawberry.Info, **kwargs
+    ) -> bool:
+        return False
+
+
+@strawberry.type
+class Fruit(relay.Node):
+    code: relay.NodeID[int]
+    name: str
+    weight: float
+
+    @classmethod
+    def resolve_nodes(
+        cls,
+        *,
+        info: strawberry.Info,
+        node_ids: Iterable[str],
+    ):
+        return []
+
+
+@strawberry.type
+class Query:
+    node: relay.Node = relay.node()
+
+    @relay.connection(
+        relay.ListConnection[Fruit] | None, permission_classes=[IsAuthenticated()]
+    )
+    def fruits(self) -> Iterable[Fruit]:
+        # This can be a database query, a generator, an async generator, etc
+        return all_fruits.values()
+```

strawberry/annotation.py

@@ -208,7 +208,7 @@ def create_optional(self, evaled_type: Any) -> StrawberryOptional:
         )
 
         # Note that passing a single type to `Union` is equivalent to not using `Union`
-        # at all. This allows us to not di any checks for how many types have been
+        # at all. This allows us to not do any checks for how many types have been
         # passed as we can safely use `Union` for both optional types
         # (e.g. `Optional[str]`) and optional unions (e.g.
         # `Optional[Union[TypeA, TypeB]]`)

strawberry/relay/fields.py

@@ -24,9 +24,8 @@
     Type,
     Union,
     cast,
-    overload,
 )
-from typing_extensions import Annotated, get_origin
+from typing_extensions import Annotated, get_args, get_origin
 
 from strawberry.annotation import StrawberryAnnotation
 from strawberry.extensions.field_extension import (
@@ -44,9 +43,9 @@
 from strawberry.types.fields.resolver import StrawberryResolver
 from strawberry.types.lazy_type import LazyType
 from strawberry.utils.aio import asyncgen_to_list
-from strawberry.utils.typing import eval_type, is_generic_alias
+from strawberry.utils.typing import eval_type, is_generic_alias, is_union
 
-from .types import Connection, GlobalID, Node, NodeIterableType, NodeType
+from .types import Connection, GlobalID, Node
 
 if TYPE_CHECKING:
     from typing_extensions import Literal
@@ -233,7 +232,11 @@ def apply(self, field: StrawberryField) -> None:
             f_type = f_type.resolve_type()
             field.type = f_type
 
+        if isinstance(f_type, StrawberryOptional):
+            f_type = f_type.of_type
+
         type_origin = get_origin(f_type) if is_generic_alias(f_type) else f_type
+
         if not isinstance(type_origin, type) or not issubclass(type_origin, Connection):
             raise RelayWrongAnnotationError(field.name, cast(type, field.origin))
 
@@ -253,13 +256,18 @@ def apply(self, field: StrawberryField) -> None:
                 None,
             )
 
+        if is_union(resolver_type):
+            # TODO: actually check if is optional and get correct type
+            resolver_type = get_args(resolver_type)[0]
+
         origin = get_origin(resolver_type)
+
         if origin is None or not issubclass(
             origin, (Iterator, Iterable, AsyncIterator, AsyncIterable)
         ):
             raise RelayWrongResolverAnnotationError(field.name, field.base_resolver)
 
-        self.connection_type = cast(Type[Connection[Node]], field.type)
+        self.connection_type = cast(Type[Connection[Node]], f_type)
 
     def resolve(
         self,
@@ -327,44 +335,17 @@ def node(*args: Any, **kwargs: Any) -> StrawberryField:
         return field(*args, **kwargs)
 
 
-@overload
-def connection(
-    graphql_type: Optional[Type[Connection[NodeType]]] = None,
-    *,
-    resolver: Optional[_RESOLVER_TYPE[NodeIterableType[Any]]] = None,
-    name: Optional[str] = None,
-    is_subscription: bool = False,
-    description: Optional[str] = None,
-    init: Literal[True] = True,
-    permission_classes: Optional[List[Type[BasePermission]]] = None,
-    deprecation_reason: Optional[str] = None,
-    default: Any = dataclasses.MISSING,
-    default_factory: Union[Callable[..., object], object] = dataclasses.MISSING,
-    metadata: Optional[Mapping[Any, Any]] = None,
-    directives: Optional[Sequence[object]] = (),
-    extensions: List[FieldExtension] = (),  # type: ignore
-) -> Any: ...
-
-
-@overload
-def connection(
-    graphql_type: Optional[Type[Connection[NodeType]]] = None,
-    *,
-    name: Optional[str] = None,
-    is_subscription: bool = False,
-    description: Optional[str] = None,
-    permission_classes: Optional[List[Type[BasePermission]]] = None,
-    deprecation_reason: Optional[str] = None,
-    default: Any = dataclasses.MISSING,
-    default_factory: Union[Callable[..., object], object] = dataclasses.MISSING,
-    metadata: Optional[Mapping[Any, Any]] = None,
-    directives: Optional[Sequence[object]] = (),
-    extensions: List[FieldExtension] = (),  # type: ignore
-) -> StrawberryField: ...
+# we used to have `Type[Connection[NodeType]]` here, but that when we added
+# support for making the Connection type optional, we had to change it to
+# `Any` because otherwise it wouldn't be type check since `Optional[Connection[Something]]`
+# is not a `Type`, but a special form, see https://discuss.python.org/t/is-annotated-compatible-with-type-t/43898/46
+# for more information, and also https://peps.python.org/pep-0747/, which is currently
+# in draft status (and no type checker supports it yet)
+ConnectionGraphQLType = Any
 
 
 def connection(
-    graphql_type: Optional[Type[Connection[NodeType]]] = None,
+    graphql_type: Optional[ConnectionGraphQLType] = None,
     *,
     resolver: Optional[_RESOLVER_TYPE[Any]] = None,
     name: Optional[str] = None,
@@ -379,7 +360,7 @@ def connection(
     extensions: List[FieldExtension] = (),  # type: ignore
     # This init parameter is used by pyright to determine whether this field
     # is added in the constructor or not. It is not used to change
-    # any behavior at the moment.
+    # any behaviour at the moment.
     init: Literal[True, False, None] = None,
 ) -> Any:
     """Annotate a property or a method to create a relay connection field.

strawberry/schema/subscribe.py

@@ -138,7 +138,7 @@ async def subscribe(
         middleware_manager,
         execution_context_class,
     )
-    # GrapQL-core might return an initial error result instead of an async iterator.
+    # GraphQL-core might return an initial error result instead of an async iterator.
     # This happens when "there was an immediate error" i.e resolver is not an async iterator.
     # To overcome this while maintaining the extension contexts we do this trick.
     first = await asyncgen.__anext__()

tests/relay/test_connection.py

@@ -0,0 +1,125 @@
+import sys
+from typing import Any, Iterable, List, Optional
+from typing_extensions import Self
+
+import pytest
+
+import strawberry
+from strawberry.permission import BasePermission
+from strawberry.relay import Connection, Node
+
+
+@strawberry.type
+class User(Node):
+    id: strawberry.relay.NodeID
+    name: str = "John"
+
+    @classmethod
+    def resolve_nodes(
+        cls, *, info: strawberry.Info, node_ids: List[Any], required: bool
+    ) -> List[Self]:
+        return [cls() for _ in node_ids]
+
+
+@strawberry.type
+class UserConnection(Connection[User]):
+    @classmethod
+    def resolve_connection(
+        cls,
+        nodes: Iterable[User],
+        *,
+        info: Any,
+        after: Optional[str] = None,
+        before: Optional[str] = None,
+        first: Optional[int] = None,
+        last: Optional[int] = None,
+    ) -> Optional[Self]:
+        return None
+
+
+class TestPermission(BasePermission):
+    message = "Not allowed"
+
+    def has_permission(self, source, info, **kwargs: Any):
+        return False
+
+
+def test_nullable_connection_with_optional():
+    @strawberry.type
+    class Query:
+        @strawberry.relay.connection(Optional[UserConnection])
+        def users(self) -> Optional[List[User]]:
+            return None
+
+    schema = strawberry.Schema(query=Query)
+    query = """
+        query {
+            users {
+                edges {
+                    node {
+                        name
+                    }
+                }
+            }
+        }
+    """
+
+    result = schema.execute_sync(query)
+    assert result.data == {"users": None}
+    assert not result.errors
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 10),
+    reason="pipe syntax for union is only available on python 3.10+",
+)
+def test_nullable_connection_with_pipe():
+    @strawberry.type
+    class Query:
+        @strawberry.relay.connection(UserConnection | None)
+        def users(self) -> List[User] | None:
+            return None
+
+    schema = strawberry.Schema(query=Query)
+    query = """
+        query {
+            users {
+                edges {
+                    node {
+                        name
+                    }
+                }
+            }
+        }
+    """
+
+    result = schema.execute_sync(query)
+    assert result.data == {"users": None}
+    assert not result.errors
+
+
+def test_nullable_connection_with_permission():
+    @strawberry.type
+    class Query:
+        @strawberry.relay.connection(
+            Optional[UserConnection], permission_classes=[TestPermission]
+        )
+        def users(self) -> Optional[List[User]]:
+            return None
+
+    schema = strawberry.Schema(query=Query)
+    query = """
+        query {
+            users {
+                edges {
+                    node {
+                        name
+                    }
+                }
+            }
+        }
+    """
+
+    result = schema.execute_sync(query)
+    assert result.data == {"users": None}
+    assert result.errors[0].message == "Not allowed"