Queries & ObjectTypes

Introduction

Graphene-Django offers a host of features for performing GraphQL queries.

Graphene-Django ships with a special DjangoObjectType that automatically transforms a Django Model into a ObjectType for you.

Full example

# my_app/schema.py

import graphene

from graphene_django.types import DjangoObjectType
from .models import Question


class QuestionType(DjangoObjectType):
    class Meta:
        model = Question


class Query:
    questions = graphene.List(QuestionType)
    question = graphene.Field(QuestionType, question_id=graphene.String())

    def resolve_questions(self, info, **kwargs):
        # Querying a list
        return Question.objects.all()

    def resolve_question(self, info, question_id):
        # Querying a single question
        return Question.objects.get(pk=question_id)

Fields

By default, DjangoObjectType will present all fields on a Model through GraphQL. If you don’t want to do this you can change this by setting either only_fields and exclude_fields.

only_fields

Show only these fields on the model:

class QuestionType(DjangoObjectType):
    class Meta:
        model = Question
        only_fields = ('question_text')

exclude_fields

Show all fields except those in exclude_fields:

class QuestionType(DjangoObjectType):
    class Meta:
        model = Question
        exclude_fields = ('question_text')

Customised fields

You can completely overwrite a field, or add new fields, to a DjangoObjectType using a Resolver:

class QuestionType(DjangoObjectType):

    class Meta:
        model = Question
        exclude_fields = ('question_text')

    extra_field = graphene.String()

    def resolve_extra_field(self, info):
        return 'hello!'

Default QuerySet

If you are using DjangoObjectType you can define a custom get_queryset method. Use this to control filtering on the ObjectType level instead of the Query object level.

from graphene_django.types import DjangoObjectType
from .models import Question


class QuestionType(DjangoObjectType):
    class Meta:
        model = Question

    @classmethod
    def get_queryset(cls, queryset, info):
        if info.context.user.is_anonymous:
            return queryset.filter(published=True)
        return queryset

Resolvers

When a GraphQL query is received by the Schema object, it will map it to a “Resolver” related to it.

This resolve method should follow this format:

def resolve_foo(self, info, **kwargs):

Where “foo” is the name of the field declared in the Query object.

class Query:
    foo = graphene.List(QuestionType)

    def resolve_foo(self, info, **kwargs):
        id = kwargs.get('id')
        return QuestionModel.objects.get(id)

Arguments

Additionally, Resolvers will receive any arguments declared in the field definition. This allows you to provide input arguments in your GraphQL server and can be useful for custom queries.

class Query:
    question = graphene.Field(Question, foo=graphene.String(), bar=graphene.Int())

    def resolve_question(self, info, foo, bar):
        # If `foo` or `bar` are declared in the GraphQL query they will be here, else None.
        return Question.objects.filter(foo=foo, bar=bar).first()

Info

The info argument passed to all resolve methods holds some useful information. For Graphene-Django, the info.context attribute is the HTTPRequest object that would be familiar to any Django developer. This gives you the full functionality of Django’s HTTPRequest in your resolve methods, such as checking for authenticated users:

def resolve_questions(self, info, **kwargs):
    # See if a user is authenticated
    if info.context.user.is_authenticated():
        return Question.objects.all()
    else:
        return Question.objects.none()

Plain ObjectTypes

With Graphene-Django you are not limited to just Django Models - you can use the standard ObjectType to create custom fields or to provide an abstraction between your internal Django models and your external API.

import graphene
from .models import Question


class MyQuestion(graphene.ObjectType):
    text = graphene.String()


class Query:
    question = graphene.Field(MyQuestion, question_id=graphene.String())

    def resolve_question(self, info, question_id):
        question = Question.objects.get(pk=question_id)
        return MyQuestion(
            text=question.question_text
        )

For more information and more examples, please see the core object type documentation.

Relay

Relay with Graphene-Django gives us some additional features:

  • Pagination and slicing.
  • An abstract id value which contains enough info for the server to know its type and its id.

There is one additional import and a single line of code needed to adopt this:

Full example

See the Relay documentation on the core graphene pages for more information on customizing the Relay experience.

from graphene import relay
from graphene_django import DjangoObjectType
from .models import Question


class QuestionType(DjangoObjectType):
    class Meta:
        model = Question
        interfaces = (relay.Node,)


class QuestionConnection(relay.Connection):
    class Meta:
        node = QuestionType


class Query:
    questions = relay.ConnectionField(QuestionConnection)

    def resolve_questions(root, info, **kwargs):
        return Question.objects.all()

You can now execute queries like:

{
    questions (first: 2, after: "YXJyYXljb25uZWN0aW9uOjEwNQ==") {
        pageInfo {
        startCursor
        endCursor
        hasNextPage
        hasPreviousPage
        }
        edges {
        cursor
        node {
            id
            question_text
        }
        }
    }
}

Which returns:

{
    "data": {
        "questions": {
        "pageInfo": {
            "startCursor": "YXJyYXljb25uZWN0aW9uOjEwNg==",
            "endCursor": "YXJyYXljb25uZWN0aW9uOjEwNw==",
            "hasNextPage": true,
            "hasPreviousPage": false
        },
        "edges": [
            {
            "cursor": "YXJyYXljb25uZWN0aW9uOjEwNg==",
            "node": {
                "id": "UGxhY2VUeXBlOjEwNw==",
                "question_text": "How did we get here?"
            }
            },
            {
            "cursor": "YXJyYXljb25uZWN0aW9uOjEwNw==",
            "node": {
                "id": "UGxhY2VUeXBlOjEwOA==",
                "name": "Where are we?"
            }
            }
        ]
        }
    }
}

Note that relay implements pagination capabilities automatically, adding a pageInfo element, and including cursor on nodes. These elements are included in the above example for illustration.

To learn more about Pagination in general, take a look at Pagination on the GraphQL community site.