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.descriptors 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.

Optimizing polymorphic queries

The optimizer has dedicated support for polymorphic queries, that is, fields which return an interface. The optimizer will handle optimizing any subtypes of the interface as necessary. This is supported on top level queries as well as relations between models. See the following sections for how this interacts with your models.

Using Django Polymorphic

If you are already using the Django Polymorphic library, polymorphic queries work out of the box.

from django.db import models
from polymorphic.models import PolymorphicModel

class Project(PolymorphicModel):
    topic = models.CharField(max_length=255)

class ResearchProject(Project):
    supervisor = models.CharField(max_length=30)

class ArtProject(Project):
    artist = models.CharField(max_length=30)

import strawberry
import strawberry_django
from . import models


@strawberry_django.interface(models.Project)
class ProjectType:
    topic: strawberry.auto


@strawberry_django.type(models.ResearchProject)
class ResearchProjectType(ProjectType):
    supervisor: strawberry.auto


@strawberry_django.type(models.ArtProject)
class ArtProjectType(ProjectType):
    artist: strawberry.auto


@strawberry.type
class Query:
    projects: list[ProjectType] = strawberry_django.field()

The projects field will return either ResearchProjectType or ArtProjectType, matching on whether it is a ResearchProject or ArtProject. The optimizer will make sure to only select those fields from subclasses which are requested in the GraphQL query in the same way that it does normally.

Warning

The optimizer does not filter your QuerySet and Django will return all instances of your model, regardless of whether their type exists in your GraphQL schema or not. Make sure you have a corresponding type for every model subclass or add a get_queryset method to your GraphQL interface type to filter out unwanted subtypes. Otherwise you might receive an error like Abstract type 'ProjectType' must resolve to an Object type at runtime for field 'Query.projects'.

Using Model-Utils InheritanceManager

Models using InheritanceManager from django-model-utils are also supported.

from django.db import models
from model_utils.managers import InheritanceManager

class Project(models.Model):
    topic = models.CharField(max_length=255)

    objects = InheritanceManager()

class ResearchProject(Project):
    supervisor = models.CharField(max_length=30)

class ArtProject(Project):
    artist = models.CharField(max_length=30)

import strawberry
import strawberry_django
from . import models


@strawberry_django.interface(models.Project)
class ProjectType:
    topic: strawberry.auto


@strawberry_django.type(models.ResearchProject)
class ResearchProjectType(ProjectType):
    supervisor: strawberry.auto


@strawberry_django.type(models.ArtProject)
class ArtProjectType(ProjectType):
    artist: strawberry.auto


@strawberry.type
class Query:
    projects: list[ProjectType] = strawberry_django.field()

The projects field will return either ResearchProjectType or ArtProjectType, matching on whether it is a ResearchProject or ArtProject. The optimizer automatically calls select_subclasses , passing in any subtypes present in your schema.

Warning

Note

If you have polymorphic relations (as in: a field that points to a model with subclasses), you need to make sure the manager being used to look up the related model is an InheritanceManager . Strawberry Django uses the model’s base manager by default, which is different from the standard objects . Either change your base manager to also be an InheritanceManager or set Strawberry Django to use the default manager: DjangoOptimizerExtension(prefetch_custom_queryset=True) .

Custom polymorphic solution

The optimizer also supports polymorphism even if your models are not polymorphic. resolve_type in the GraphQL interface type is used to tell GraphQL the actual type that should be used.

from django.db import models

class Project(models.Model):
    topic = models.CharField(max_length=255)
    supervisor = models.CharField(max_length=30)
    artist = models.CharField(max_length=30)

import strawberry
import strawberry_django
from . import models


@strawberry_django.interface(models.Project)
class ProjectType:
    topic: strawberry.auto

    @classmethod
    def resolve_type(cls, value, info, parent_type) -> str:
        if not isinstance(value, models.Project):
            raise TypeError()
        if value.artist:
            return 'ArtProjectType'
        if value.supervisor:
            return 'ResearchProjectType'
        raise TypeError()

    @classmethod
    def get_queryset(cls, qs, info):
        return qs


@strawberry_django.type(models.ResearchProject)
class ResearchProjectType(ProjectType):
    supervisor: strawberry.auto


@strawberry_django.type(models.ArtProject)
class ArtProjectType(ProjectType):
    artist: strawberry.auto


@strawberry.type
class Query:
    projects: list[ProjectType] = strawberry_django.field()

Warning

Make sure to add get_queryset to your interface type, to force the optimizer to use prefetch_related , otherwise this technique will not work for relation fields.