DjangoOptimizerExtension not optimizing when fragments are used and field is queried twice

[edomora97]

Given this schema (simplified from the demo):

schema.py

from typing import List, cast

from strawberry_django_plus import gql
from strawberry_django_plus.directives import SchemaDirectiveExtension
from strawberry_django_plus.optimizer import DjangoOptimizerExtension

from .models import Issue, Tag


@gql.django.type(Issue)
class IssueType:
    name: gql.auto
    tags: List["TagType"]


@gql.django.type(Tag)
class TagType:
    name: gql.auto
    issues: List[IssueType]


@gql.type
class Query:
    issue_list: List[IssueType] = gql.django.field()


schema = gql.Schema(
    query=Query,
    extensions=[
        SchemaDirectiveExtension,
        DjangoOptimizerExtension,
    ],
)

And given these two equivalent queries:

slow.graphql

query Slow {
  issueList {
    name
    tags {
      ...A
    }
    tags {
      name
    }
  }
}

fragment A on TagType {
  issues {
    ...B
  }
}

fragment B on IssueType {
  name
}

fast.graphql (obtained by clicking on "Merge fragments into query" in GraphiQL)

query Fast {
  issueList {
    name
    tags {
      issues {
        name
      }
      name
    }
  }
}

Initializing the database with this queries:

Details

INSERT INTO demo_issue (id, name, priority)
VALUES (1, 'issue1', 1), (2, 'issue2', 2), (3, 'issue3', 3);

INSERT INTO demo_tag (id, name)
VALUES (1, 'tag1'), (2, 'tag2'), (3, 'tag3');

INSERT INTO demo_issue_tags (issue_id, tag_id)
VALUES (1, 1), (1, 2), (1, 3), (2, 1), (2, 2), (2, 3), (3, 1), (3, 2), (3, 3);

Slow is experiencing the N+1 queries problem, while Fast is not.

Using GraphiQL and the Django toolbar I can see that Fast is making 3 queries:

While Slow is making 11:

Note that moving the field name from issueList into the fragment A doesn't trigger the issue.

[blueyed]

@edomora97
btw/OT:

Using GraphiQL and the Django toolbar

How does this work for you?
I'm using https://github.com/przemub/django-graphiql-strawberry-debug-toolbar, but despite the fix from przemub/django-graphiql-strawberry-debug-toolbar#1 it appears to not be working for me anymore currently.

[bellini666]

Hey @edomora97 , thanks for reporting this.

The optimizer does take fragments into consideration, but your example might be hitting a corner case that it is not considering. The code that inspects the query is

strawberry-django-plus/strawberry_django_plus/utils/inspect.py

Line 193 in 87fb094

def get_selections(

, with the fragment handling being done in this elif clause.

I'll try to take a look at that by the end of the week, but if you have time to take a look at this, feel free to open a PR that fixes it and I'll glagly review it :)

@blueyed this lib provides a fix to the toolbar to make it work, even with async views. Try using it: https://blb-ventures.github.io/strawberry-django-plus/debug-toolbar/

[LucasPickering]

@bellini666 Did you ever get a chance to look at this one? I'm running into the same issue.