fix(optimizer): Avoid merging prefetches when using aliases (#698)

strawberry_django/optimizer.py

@@ -5,7 +5,7 @@
 import copy
 import dataclasses
 import itertools
-from collections import defaultdict
+from collections import Counter, defaultdict
 from collections.abc import Callable
 from typing import (
     TYPE_CHECKING,
@@ -58,6 +58,7 @@
 from .utils.inspect import (
     PrefetchInspector,
     get_model_field,
+    get_model_fields,
     get_possible_type_definitions,
 )
 from .utils.typing import (
@@ -1035,19 +1036,29 @@ def _get_model_hints(
     if pk is not None:
         store.only.append(pk.attname)
 
-    for f_selections in _get_selections(info, parent_type).values():
-        field_data = _get_field_data(
-            f_selections,
-            object_definition,
-            schema,
-            parent_type=parent_type,
-            info=info,
+    selections = [
+        field_data
+        for f_selection in _get_selections(info, parent_type).values()
+        if (
+            field_data := _get_field_data(
+                f_selection,
+                object_definition,
+                schema,
+                parent_type=parent_type,
+                info=info,
+            )
         )
-        if field_data is None:
+        is not None
+    ]
+    fields_counter = Counter(field_data[0] for field_data in selections)
+
+    for field, f_definition, f_selection, f_info in selections:
+        # If a field is selected more than once in the query, that means it is being
+        # aliased. In this case, optimizing it would make one query to affect the other,
+        # resulting in wrong results for both.
+        if fields_counter[field] > 1:
             continue
 
-        field, f_definition, f_selection, f_info = field_data
-
         # Add annotations from the field if they exist
         if field_store := _get_hints_from_field(field, f_info=f_info, prefix=prefix):
             store |= field_store
@@ -1089,6 +1100,30 @@ def _get_model_hints(
             store.only.extend(inner_store.only)
             store.select_related.extend(inner_store.select_related)
 
+    # In case we skipped optimization for a relation, we might end up with a new QuerySet
+    # which would not select its parent relation field on `.only()`, causing n+1 issues.
+    # Make sure that in this case we also select it.
+    if level == 0 and store.only and info.path.prev:
+        own_fk_fields = [
+            field
+            for field in get_model_fields(model).values()
+            if isinstance(field, models.ForeignKey)
+        ]
+
+        path = info.path
+        while path := path.prev:
+            type_ = schema.get_type_by_name(path.typename)
+            if not isinstance(type_, StrawberryObjectDefinition):
+                continue
+
+            if not (strawberry_django_type := get_django_definition(type_.origin)):
+                continue
+
+            for field in own_fk_fields:
+                if field.related_model is strawberry_django_type.model:
+                    store.only.append(field.attname)
+                    break
+
     return store
 
 

tests/test_optimizer.py

@@ -308,14 +308,6 @@ def test_query_forward_with_fragments(db, gql_client: GraphQLTestClient):
                 }
                 ... milestoneFrag
               }
-              milestoneAgain: milestone {
-                name
-                project {
-                  id
-                  name
-                }
-                ... milestoneFrag
-              }
             }
           }
         }
@@ -341,7 +333,6 @@ def test_query_forward_with_fragments(db, gql_client: GraphQLTestClient):
                         "nameWithKind": f"{i.kind}: {i.name}",
                         "nameWithPriority": f"{i.kind}: {i.priority}",
                         "milestone": m_res,
-                        "milestoneAgain": m_res,
                     },
                 )
 
@@ -538,12 +529,6 @@ def test_query_prefetch_with_fragments(db, gql_client: GraphQLTestClient):
                 ... milestoneFrag
               }
             }
-            otherIssues: issues {
-              id
-              milestone {
-                ... milestoneFrag
-              }
-            }
           }
         }
       }
@@ -566,7 +551,6 @@ def test_query_prefetch_with_fragments(db, gql_client: GraphQLTestClient):
                     "name": p_res["name"],
                 },
                 "issues": [],
-                "otherIssues": [],
             }
             p_res["milestones"].append(m_res)
             for i in IssueFactory.create_batch(3, milestone=m):
@@ -585,22 +569,10 @@ def test_query_prefetch_with_fragments(db, gql_client: GraphQLTestClient):
                         },
                     },
                 )
-                m_res["otherIssues"].append(
-                    {
-                        "id": to_base64("IssueType", i.id),
-                        "milestone": {
-                            "id": m_res["id"],
-                            "project": {
-                                "id": p_res["id"],
-                                "name": p_res["name"],
-                            },
-                        },
-                    },
-                )
 
     assert len(expected) == 3
     for e in expected:
-        with assert_num_queries(3 if DjangoOptimizerExtension.enabled.get() else 8):
+        with assert_num_queries(3 if DjangoOptimizerExtension.enabled.get() else 5):
             res = gql_client.query(query, {"node_id": e["id"]})
 
         assert res.data == {"project": e}
@@ -1089,6 +1061,52 @@ def test_query_nested_connection_with_filter(db, gql_client: GraphQLTestClient):
     } == expected
 
 
+@pytest.mark.django_db(transaction=True)
+def test_query_nested_connection_with_filter_and_alias(
+    db, gql_client: GraphQLTestClient
+):
+    query = """
+      query TestQuery ($id: GlobalID!) {
+        milestone(id: $id) {
+          id
+          fooIssues: issuesWithFilters (filters: {search: "Foo"}) {
+            edges {
+              node {
+                id
+              }
+            }
+          }
+          barIssues: issuesWithFilters (filters: {search: "Bar"}) {
+            edges {
+              node {
+                id
+              }
+            }
+          }
+        }
+      }
+    """
+
+    milestone = MilestoneFactory.create()
+    issue1 = IssueFactory.create(milestone=milestone, name="Foo")
+    issue2 = IssueFactory.create(milestone=milestone, name="Foo Bar")
+    issue3 = IssueFactory.create(milestone=milestone, name="Bar Foo")
+    issue4 = IssueFactory.create(milestone=milestone, name="Bar Bin")
+
+    with assert_num_queries(3):
+        res = gql_client.query(query, {"id": to_base64("MilestoneType", milestone.pk)})
+
+    assert isinstance(res.data, dict)
+    result = res.data["milestone"]
+    assert isinstance(result, dict)
+
+    foo_expected = {to_base64("IssueType", i.pk) for i in [issue1, issue2, issue3]}
+    assert {edge["node"]["id"] for edge in result["fooIssues"]["edges"]} == foo_expected
+
+    bar_expected = {to_base64("IssueType", i.pk) for i in [issue2, issue3, issue4]}
+    assert {edge["node"]["id"] for edge in result["barIssues"]["edges"]} == bar_expected
+
+
 @pytest.mark.django_db(transaction=True)
 def test_query_with_optimizer_paginated_prefetch():
     @strawberry_django.type(Milestone, pagination=True)