graphene-django/docs/mutations.rst

Mutations

Introduction

Graphene-Django makes it easy to perform mutations.

With Graphene-Django we can take advantage of pre-existing Django features to quickly build CRUD functionality, while still using the core graphene mutation features to add custom mutations to a Django project.

Simple example

import graphene

from graphene_django import DjangoObjectType

from .models import Question


class QuestionType(DjangoObjectType):
    class Meta:
        model = Question
        fields = '__all__'


class QuestionMutation(graphene.Mutation):
    class Arguments:
        # The input arguments for this mutation
        text = graphene.String(required=True)
        id = graphene.ID()

    # The class attributes define the response of the mutation
    question = graphene.Field(QuestionType)

    @classmethod
    def mutate(cls, root, info, text, id):
        question = Question.objects.get(pk=id)
        question.text = text
        question.save()
        # Notice we return an instance of this mutation
        return QuestionMutation(question=question)


class Mutation(graphene.ObjectType):
    update_question = QuestionMutation.Field()

Django Forms

Graphene-Django comes with mutation classes that will convert the fields on Django forms into inputs on a mutation.

DjangoFormMutation

from graphene_django.forms.mutation import DjangoFormMutation

class MyForm(forms.Form):
    name = forms.CharField()

class MyMutation(DjangoFormMutation):
    class Meta:
        form_class = MyForm

MyMutation will automatically receive an input argument. This argument should be a dict where the key is name and the value is a string.

DjangoModelFormMutation

DjangoModelFormMutation will pull the fields from a ModelForm.

from graphene_django.forms.mutation import DjangoModelFormMutation

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

class PetForm(forms.ModelForm):
    class Meta:
        model = Pet
        fields = ('name',)

# This will get returned when the mutation completes successfully
class PetType(DjangoObjectType):
    class Meta:
        model = Pet
        fields = '__all__'

class PetMutation(DjangoModelFormMutation):
    pet = Field(PetType)

    class Meta:
        form_class = PetForm

PetMutation will grab the fields from PetForm and turn them into inputs. If the form is valid then the mutation will lookup the DjangoObjectType for the Pet model and return that under the key pet. Otherwise it will return a list of errors.

You can change the input name (default is input) and the return field name (default is the model name lowercase).

class PetMutation(DjangoModelFormMutation):
    class Meta:
        form_class = PetForm
        input_field_name = 'data'
        return_field_name = 'my_pet'

Form validation

Form mutations will call is_valid() on your forms.

If the form is valid then the class method perform_mutate(form, info) is called on the mutation. Override this method to change how the form is saved or to return a different Graphene object type.

If the form is not valid then a list of errors will be returned. These errors have two fields: field, a string containing the name of the invalid form field, and messages, a list of strings with the validation messages.

Django REST Framework

You can re-use your Django Rest Framework serializer with Graphene Django mutations.

You can create a Mutation based on a serializer by using the SerializerMutation base class:

from graphene_django.rest_framework.mutation import SerializerMutation

class MyAwesomeMutation(SerializerMutation):
    class Meta:
        serializer_class = MySerializer

Create/Update Operations

By default ModelSerializers accept create and update operations. To customize this use the model_operations attribute on the SerializerMutation class.

The update operation looks up models by the primary key by default. You can customize the look up with the lookup_field attribute on the SerializerMutation class.

from graphene_django.rest_framework.mutation import SerializerMutation
from .serializers import MyModelSerializer


class AwesomeModelMutation(SerializerMutation):
    class Meta:
        serializer_class = MyModelSerializer
        model_operations = ['create', 'update']
        lookup_field = 'id'

Overriding Update Queries

Use the method get_serializer_kwargs to override how updates are applied.

from graphene_django.rest_framework.mutation import SerializerMutation
from .serializers import MyModelSerializer


class AwesomeModelMutation(SerializerMutation):
    class Meta:
        serializer_class = MyModelSerializer

    @classmethod
    def get_serializer_kwargs(cls, root, info, **input):
        if 'id' in input:
            instance = Post.objects.filter(
                id=input['id'], owner=info.context.user
            ).first()
            if instance:
                return {'instance': instance, 'data': input, 'partial': True}

            else:
                raise http.Http404

        return {'data': input, 'partial': True}

Relay

You can use relay with mutations. A Relay mutation must inherit from ClientIDMutation and implement the mutate_and_get_payload method:

import graphene
from graphene import relay
from graphene_django import DjangoObjectType
from graphql_relay import from_global_id

from .queries import QuestionType


class QuestionMutation(relay.ClientIDMutation):
    class Input:
        text = graphene.String(required=True)
        id = graphene.ID()

    question = graphene.Field(QuestionType)

    @classmethod
    def mutate_and_get_payload(cls, root, info, text, id):
        question = Question.objects.get(pk=from_global_id(id)[1])
        question.text = text
        question.save()
        return QuestionMutation(question=question)

Notice that the class Arguments is renamed to class Input with relay. This is due to a deprecation of class Arguments in graphene 2.0.

Relay ClientIDMutation accept a clientIDMutation argument. This argument is also sent back to the client with the mutation result (you do not have to do anything). For services that manage a pool of many GraphQL requests in bulk, the clientIDMutation allows you to match up a specific mutation with the response.

Django Database Transactions

Django gives you a few ways to control how database transactions are managed.

Tying transactions to HTTP requests

A common way to handle transactions in Django is to wrap each request in a transaction. Set ATOMIC_REQUESTS settings to True in the configuration of each database for which you want to enable this behavior.

It works like this. Before calling GraphQLView Django starts a transaction. If the response is produced without problems, Django commits the transaction. If the view, a DjangoFormMutation or a DjangoModelFormMutation produces an exception, Django rolls back the transaction.

Warning

While the simplicity of this transaction model is appealing, it also makes it inefficient when traffic increases. Opening a transaction for every request has some overhead. The impact on performance depends on the query patterns of your application and on how well your database handles locking.

Check the next section for a better solution.

Tying transactions to mutations

A mutation can contain multiple fields, just like a query. There's one important distinction between queries and mutations, other than the name:

This means that if we send two incrementCredits mutations in one request, the first is guaranteed to finish before the second begins, ensuring that we don't end up with a race condition with ourselves.

On the other hand, if the first incrementCredits runs successfully but the second one does not, the operation cannot be retried as it is. That's why is a good idea to run all mutation fields in a transaction, to guarantee all occur or nothing occurs.

To enable this behavior for all databases set the graphene ATOMIC_MUTATIONS settings to True in your settings file:

GRAPHENE = {
    # ...
    "ATOMIC_MUTATIONS": True,
}

On the contrary, if you want to enable this behavior for a specific database, set ATOMIC_MUTATIONS to True in your database settings:

DATABASES = {
    "default": {
        # ...
        "ATOMIC_MUTATIONS": True,
    },
    # ...
}

Now, given the following example mutation:

mutation IncreaseCreditsTwice {

    increaseCredits1: increaseCredits(input: { amount: 10 }) {
        balance
        errors {
            field
            messages
        }
    }

    increaseCredits2: increaseCredits(input: { amount: -1 }) {
        balance
        errors {
            field
            messages
        }
    }

}

The server is going to return something like:

{
    "data": {
        "increaseCredits1": {
            "balance": 10.0,
            "errors": []
        },
        "increaseCredits2": {
            "balance": null,
            "errors": [
                {
                    "field": "amount",
                    "message": "Amount should be a positive number"
                }
            ]
        },
    }
}

But the balance will remain the same.