perf(listconnection): only resolve edges when edges or pageInfo are s…

…elected (#3480)

RELEASE.md

@@ -0,0 +1,8 @@
+Release type: patch
+
+This release adds an optimization to `ListConnection` such that only queries with
+`edges` or `pageInfo` in their selected fields triggers `resolve_edges`.
+
+This change is particularly useful for the `strawberry-django` extension's
+`ListConnectionWithTotalCount` and the only selected field is `totalCount`. An
+extraneous SQL query is prevented with this optimization.

strawberry/relay/types.py

@@ -38,7 +38,7 @@
 from strawberry.utils.inspect import in_async_context
 from strawberry.utils.typing import eval_type, is_classvar
 
-from .utils import from_base64, to_base64
+from .utils import from_base64, should_resolve_list_connection_edges, to_base64
 
 if TYPE_CHECKING:
     from strawberry.scalars import ID
@@ -933,6 +933,17 @@ async def resolver():
                 overfetch,
             )
 
+        if not should_resolve_list_connection_edges(info):
+            return cls(
+                edges=[],
+                page_info=PageInfo(
+                    start_cursor=None,
+                    end_cursor=None,
+                    has_previous_page=False,
+                    has_next_page=False,
+                ),
+            )
+
         edges = [
             edge_class.resolve_edge(
                 cls.resolve_node(v, info=info, **kwargs),

strawberry/relay/utils.py

@@ -2,6 +2,8 @@
 from typing import Any, Tuple, Union
 from typing_extensions import assert_never
 
+from strawberry.types.info import Info
+from strawberry.types.nodes import InlineFragment
 from strawberry.types.types import StrawberryObjectDefinition
 
 
@@ -61,3 +63,25 @@ def to_base64(type_: Union[str, type, StrawberryObjectDefinition], node_id: Any)
         raise ValueError(f"{type_} is not a valid GraphQL type or name") from e
 
     return base64.b64encode(f"{type_name}:{node_id}".encode()).decode()
+
+
+def should_resolve_list_connection_edges(info: Info) -> bool:
+    """Check if the user requested to resolve the `edges` field of a connection.
+
+    Args:
+        info:
+            The strawberry execution info resolve the type name from
+
+    Returns:
+        True if the user requested to resolve the `edges` field of a connection, False otherwise.
+
+    """
+    resolve_for_field_names = {"edges", "pageInfo"}
+    for selection_field in info.selected_fields:
+        for selection in selection_field.selections:
+            if (
+                not isinstance(selection, InlineFragment)
+                and selection.name in resolve_for_field_names
+            ):
+                return True
+    return False

tests/relay/test_types.py

@@ -1,5 +1,6 @@
 from typing import Any, AsyncGenerator, AsyncIterable, Optional, Union, cast
 from typing_extensions import assert_type
+from unittest.mock import MagicMock
 
 import pytest
 
@@ -8,7 +9,7 @@
 from strawberry.relay.utils import to_base64
 from strawberry.types.info import Info
 
-from .schema import Fruit, FruitAsync, schema
+from .schema import Fruit, FruitAsync, fruits_resolver, schema
 
 
 class FakeInfo:
@@ -255,3 +256,36 @@ def fruit(self) -> Fruit:
             return Fruit(color="red")  # pragma: no cover
 
     strawberry.Schema(query=Query)
+
+
+def test_list_connection_without_edges_or_page_info(mocker: MagicMock):
+    @strawberry.type(name="Connection", description="A connection to a list of items.")
+    class DummyListConnectionWithTotalCount(relay.ListConnection[relay.NodeType]):
+        @strawberry.field(description="Total quantity of existing nodes.")
+        def total_count(self) -> int:
+            return -1
+
+    @strawberry.type
+    class Query:
+        fruits: DummyListConnectionWithTotalCount[Fruit] = relay.connection(
+            resolver=fruits_resolver
+        )
+
+    mock = mocker.patch("strawberry.relay.types.Edge.resolve_edge")
+    schema = strawberry.Schema(query=Query)
+    ret = schema.execute_sync(
+        """
+    query {
+      fruits {
+        totalCount
+      }
+    }
+    """
+    )
+    mock.assert_not_called()
+    assert ret.errors is None
+    assert ret.data == {
+        "fruits": {
+            "totalCount": -1,
+        }
+    }