Query Optimizer

Features

The query optimizer is a must-have extension for improved performance of your schema. What it does:

Call QuerySet.select_related() on all selected foreign key relations by the query to avoid requiring an extra query to retrieve those
Call QuerySet.prefetch_related() on all selected many-to-one/many-to-many relations by the query to avoid requiring an extra query to retrieve those.
Call QuerySet.only() on all selected fields to reduce the database payload and only requesting what is actually being selected
Call QuerySet.annotate() to support any passed annotations of Query Expressions .

Those are specially useful to avoid some common GraphQL pitfalls, like the famous n+1 issue.

Enabling the extension

The automatic optimization can be enabled by adding the DjangoOptimizerExtension to your strawberry’s schema config.

import strawberry
from strawberry_django.optimizer import DjangoOptimizerExtension

schema = strawberry.Schema(
    Query,
    extensions=[
        # other extensions...
        DjangoOptimizerExtension,
    ]
)

Usage

The optimizer will try to optimize all types automatically by introspecting it. Consider the following example:

class Artist(models.Model):
    name = models.CharField()


class Album(models.Model):
    name = models.CharField()
    release_date = models.DateTimeField()
    artist = models.ForeignKey("Artist", related_name="albums")


class Song(models.Model):
    name = model.CharField()
    duration = models.DecimalField()
    album = models.ForeignKey("Album", related_name="songs")

from strawberry import auto
import strawberry_django

@strawberry_django.type(Artist)
class ArtistType:
    name: auto
    albums: list["AlbumType"]
    albums_count: int = strawberry_django.field(annotate=Count("albums"))


@strawberry_django.type(Album)
class AlbumType:
    name: auto
    release_date: auto
    artist: ArtistType
    songs: list["SongType"]


@strawberry_django.type(Song)
class SongType:
    name: auto
    duration: auto
    album_type: AlbumType


@strawberry.type
class Query:
    artist: Artist = strawberry_django.field()
    songs: List[SongType] = strawberry_django.field()

Querying for artist and songs like this:

query {
  artist {
    id
    name
    albums {
      id
      name
      songs {
        id
        name
      }
    }
    albumsCount
  }
  song {
    id
    album {
      id
      name
      artist {
        id
        name
        albums {
          id
          name
          release_date
        }
      }
    }
  }
}

Would produce an ORM query like this:

# For "artist" query
Artist.objects.all().only("id", "name").prefetch_related(
    Prefetch(
        "albums",
        queryset=Album.objects.all().only("id", "name").prefetch_related(
            Prefetch(
               "songs",
               Song.objects.all().only("id", "name"),
            )
        )
    ),
).annotate(
    albums_count=Count("albums")
)

# For "songs" query
Song.objects.all().only(
    "id",
    "album",
    "album__id",
    "album__name",
    "album__release_date",  # Note about this below
    "album__artist",
    "album__artist__id",
).select_related(
    "album",
    "album__artist",
).prefetch_related(
    Prefetch(
       "album__artist__albums",
        Album.objects.all().only("id", "name", "release_date"),
    )
)

Note

Even though album__release_date field was not selected here, it got selected in the prefetch query later. Since Django caches known objects, we have to select it here or else it would trigger extra queries latter.

Optimization hints

Sometimes you will have a custom resolver which cannot be automatically optimized by the extension. Take this for example:

class OrderItem(models.Model):
    price = models.DecimalField()
    quantity = models.IntegerField()

    @property
    def total(self) -> decimal.Decimal:
        return self.price * self.quantity

from strawberry import auto
import strawberry_django

@strawberry_django.type(models.OrderItem)
class OrderItem:
    price: auto
    quantity: auto
    total: auto

In this case, if only total is requested it would trigger an extra query for both price and quantity because both had their value retrievals defered by the optimizer.

A solution in this case would be to “tell the optimizer” how to optimize that field:

from strawberry import auto
import strawberry_django

@strawberry_django.type(models.OrderItem)
class OrderItem:
    price: auto
    quantity: auto
    total: auto = strawberry_django.field(
        only=["price", "quantity"],
    )

Or if you are using a custom resolver:

import decimal

from strawberry import auto
import strawberry_django

@strawberry_django.type(models.OrderItem)
class OrderItem:
    price: auto
    quantity: auto

    @strawberry_django.field(only=["price", "quantity"])
    def total(self, root: models.OrderItem) -> decimal.Decimal:
        return root.price * root.quantity  # or root.total directly

The following options are accepted for optimizer hints:

only : a list of fields in the same format as accepted by QuerySet.only()
select_related : a list of relations to join using QuerySet.select_related()
prefetch_related : a list of relations to prefetch using QuerySet.prefetch_related() . The options here are strings or a callable in the format of Callable[[Info], Prefetch] (e.g. prefetch_related=[lambda info: Prefetch(...)] )
annotate : a dict of expressions to annotate using QuerySet.annotate() . The keys of this dict are strings, and each value is a Query Expression or a callable in the format of Callable[[Info], BaseExpression] (e.g. annotate={"total": lambda info: Sum(...)} )

Optimization hints on model (ModelProperty)

It is also possible to include type hints directly in the models’ @property to allow it to be resolved with auto , while the GraphQL schema doesn’t have to worry about its internal logic.

For that this integration provides 2 decorators that can be used:

strawberry_django.model_property : similar to @property but accepts optimization hints
strawberry_django.cached_model_property : similar to @cached_property but accepts optimization hints

The example in the previous section could be written using @model_property like this:

from strawberry_django import model_property

class OrderItem(models.Model):
    price = models.DecimalField()
    quantity = models.IntegerField()

    @model_property(only=["price", "quantity"])
    def total(self) -> decimal.Decimal:
        return self.price * self.quantity

from strawberry import auto
import strawberry_django

@strawberry_django.type(models.OrderItem)
class OrderItem:
    price: auto
    quantity: auto
    total: auto

total now will be properly optimized since it points to a @model_property decorated attribute, which contains the required information for optimizing it.