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Custom fields🔗

GraphQL types can have non-model fields using custom resolvers.

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import graphene
from example_project.app.models import HousingCompany

from query_optimizer import DjangoObjectType


class HousingCompanyType(DjangoObjectType):
    class Meta:
        model = HousingCompany

    greeting = graphene.String()

    def resolve_greeting(root: HousingCompany, info) -> str:
        return f"Hello World!"

If the custom type requires fields from its related models to resolve, you have a few options.

AnnotatedField🔗

This field can be used to add annotations to the queryset when the field is requested.

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import graphene
from django.db.models import F, Value
from example_project.app.models import HousingCompany

from query_optimizer import DjangoObjectType, AnnotatedField  # new import


class HousingCompanyType(DjangoObjectType):
    class Meta:
        model = HousingCompany

    greeting = AnnotatedField(graphene.String, expression=Value("Hello ") + F("name"))

Note that only a single annotation can be added, however, you can use the aliases parameter to help with more complex annotations.

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import graphene
from django.db.models import F, Value
from example_project.app.models import HousingCompany

from query_optimizer import DjangoObjectType, AnnotatedField


class HousingCompanyType(DjangoObjectType):
    class Meta:
        model = HousingCompany

    greeting = AnnotatedField(
        graphene.String,
        expression=F("hello") + F("name"),
        aliases={"hello": Value("Hello ")},  # very complex!
    )

MultiField🔗

This field can be used to add multiple fields to the queryset when the field is requested.

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import graphene
from example_project.app.models import HousingCompany

from query_optimizer import DjangoObjectType, MultiField  # new import


class HousingCompanyType(DjangoObjectType):
    class Meta:
        model = HousingCompany

    greeting = MultiField(graphene.String, fields=["pk", "name"])

    def resolve_greeting(root: HousingCompany, info) -> str:
        return f"Hello {root.name} ({root.pk})!"

Note that this can only be used for fields on the same model.

ManuallyOptimizedField🔗

This is the most powerful custom field type, which allows defining a custom method to manually optimize the queryset when the field is requested. This allows for optimization strategies that are not possible with the other fields.

Note: You shouldn't default to using this field, as it can break the optimization if you are not careful in considering other optimization already in the optimizer.

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import graphene
from django.db.models import QuerySet
from example_project.app.models import HousingCompany

from query_optimizer import DjangoObjectType, ManuallyOptimizedField  # new import
from query_optimizer.optimizer import QueryOptimizer  # for type hinting


class HousingCompanyType(DjangoObjectType):
    class Meta:
        model = HousingCompany

    extra = ManuallyOptimizedField(graphene.String)

    @staticmethod
    def optimize_extra(queryset: QuerySet, optimizer: QueryOptimizer, **kwargs) -> QuerySet:
        # Do any optimizations here, returning the queryset.
        return queryset

    def resolve_extra(root: HousingCompany, info) -> str:
        # Still needs a resolver.
        return ...

Note that this can only be used for fields on the same model.

The field_name argument🔗

RelatedField, DjangoListField, DjangoConnectionField have a field_name argument that can be used to specify the field name in the queryset if it's different from the field name in the model.

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from example_project.app.models import HousingCompany

from query_optimizer import DjangoObjectType, DjangoListField  # new import


class HousingCompanyType(DjangoObjectType):
    class Meta:
        model = HousingCompany

    developers_alt = DjangoListField("...", field_name="developers")

This marks the field as being for the same relation as the field_name is on the model, and it will resolve the field as if it was that relation. This is achieved by using the Prefetch("developers", qs, to_attr="developers_alt") feature from Django.