.. _queries-objecttypes:
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
~~~~~~~~~~~~
.. code:: python
# my_app/schema.py
import graphene
from graphene_django import DjangoObjectType
from .models import Question
class QuestionType(DjangoObjectType):
class Meta:
model = Question
fields = ("id", "question_text")
class Query(graphene.ObjectType):
questions = graphene.List(QuestionType)
question_by_id = graphene.Field(QuestionType, id=graphene.String())
def resolve_questions(root, info, **kwargs):
# Querying a list
return Question.objects.all()
def resolve_question_by_id(root, info, id):
# Querying a single question
return Question.objects.get(pk=id)
Specifying which fields to include
----------------------------------
By default, ``DjangoObjectType`` will present all fields on a Model through GraphQL.
If you only want a subset of fields to be present, you can do so using
``fields`` or ``exclude``. It is strongly recommended that you explicitly set
all fields that should be exposed using the fields attribute.
This will make it less likely to result in unintentionally exposing data when
your models change.
``fields``
~~~~~~~~~~
Show **only** these fields on the model:
.. code:: python
from graphene_django import DjangoObjectType
from .models import Question
class QuestionType(DjangoObjectType):
class Meta:
model = Question
fields = ("id", "question_text")
You can also set the ``fields`` attribute to the special value ``"__all__"`` to indicate that all fields in the model should be used.
For example:
.. code:: python
from graphene_django import DjangoObjectType
from .models import Question
class QuestionType(DjangoObjectType):
class Meta:
model = Question
fields = "__all__"
``exclude``
~~~~~~~~~~~
Show all fields **except** those in ``exclude``:
.. code:: python
from graphene_django import DjangoObjectType
from .models import Question
class QuestionType(DjangoObjectType):
class Meta:
model = Question
exclude = ("question_text",)
Customising fields
------------------
You can completely overwrite a field, or add new fields, to a ``DjangoObjectType`` using a Resolver:
.. code:: python
from graphene_django import DjangoObjectType
from .models import Question
class QuestionType(DjangoObjectType):
class Meta:
model = Question
fields = ("id", "question_text")
extra_field = graphene.String()
def resolve_extra_field(self, info):
return "hello!"
Choices to Enum conversion
~~~~~~~~~~~~~~~~~~~~~~~~~~
By default Graphene-Django will convert any Django fields that have `choices`_
defined into a GraphQL enum type.
.. _choices: https://docs.djangoproject.com/en/2.2/ref/models/fields/#choices
For example the following ``Model`` and ``DjangoObjectType``:
.. code:: python
from django.db import models
from graphene_django import DjangoObjectType
class PetModel(models.Model):
kind = models.CharField(
max_length=100,
choices=(("cat", "Cat"), ("dog", "Dog"))
)
class Pet(DjangoObjectType):
class Meta:
model = PetModel
fields = ("id", "kind",)
Results in the following GraphQL schema definition:
.. code::
type Pet {
id: ID!
kind: PetModelKind!
}
enum PetModelKind {
CAT
DOG
}
You can disable this automatic conversion by setting
``convert_choices_to_enum`` attribute to ``False`` on the ``DjangoObjectType``
``Meta`` class.
.. code:: python
from graphene_django import DjangoObjectType
from .models import PetModel
class Pet(DjangoObjectType):
class Meta:
model = PetModel
fields = ("id", "kind",)
convert_choices_to_enum = False
.. code::
type Pet {
id: ID!
kind: String!
}
You can also set ``convert_choices_to_enum`` to a list of fields that should be
automatically converted into enums:
.. code:: python
from graphene_django import DjangoObjectType
from .models import PetModel
class Pet(DjangoObjectType):
class Meta:
model = PetModel
fields = ("id", "kind",)
convert_choices_to_enum = ["kind"]
**Note:** Setting ``convert_choices_to_enum = []`` is the same as setting it to
``False``.
Related models
--------------
Say you have the following models:
.. code:: python
from django.db import models
class Category(models.Model):
foo = models.CharField(max_length=256)
class Question(models.Model):
category = models.ForeignKey(Category, on_delete=models.CASCADE)
When ``Question`` is published as a ``DjangoObjectType`` and you want to add ``Category`` as a query-able field like so:
.. code:: python
from graphene_django import DjangoObjectType
from .models import Question
class QuestionType(DjangoObjectType):
class Meta:
model = Question
fields = ("category",)
Then all query-able related models must be defined as DjangoObjectType subclass,
or they will fail to show if you are trying to query those relation fields. You only
need to create the most basic class for this to work:
.. code:: python
from graphene_django import DjangoObjectType
from .models import Category
class CategoryType(DjangoObjectType):
class Meta:
model = Category
fields = ("foo",)
.. _django-objecttype-get-queryset:
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.
.. code:: python
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:
.. code:: python
def resolve_foo(parent, info, **kwargs):
Where "foo" is the name of the field declared in the ``Query`` object.
.. code:: python
import graphene
from .models import Question
from .types import QuestionType
class Query(graphene.ObjectType):
foo = graphene.List(QuestionType)
def resolve_foo(root, info):
id = kwargs.get("id")
return Question.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.
.. code:: python
import graphene
from .models import Question
from .types import QuestionType
class Query(graphene.ObjectType):
question = graphene.Field(
QuestionType,
foo=graphene.String(),
bar=graphene.Int()
)
def resolve_question(root, 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:
.. code:: python
import graphene
from .models import Question
from .types import QuestionType
class Query(graphene.ObjectType):
questions = graphene.List(QuestionType)
def resolve_questions(root, info):
# See if a user is authenticated
if info.context.user.is_authenticated():
return Question.objects.all()
else:
return Question.objects.none()
DjangoObjectTypes
~~~~~~~~~~~~~~~~~
A Resolver that maps to a defined `DjangoObjectType` should only use methods that return a queryset.
Queryset methods like `values` will return dictionaries, use `defer` instead.
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.
.. code:: python
import graphene
from .models import Question
class MyQuestion(graphene.ObjectType):
text = graphene.String()
class Query(graphene.ObjectType):
question = graphene.Field(MyQuestion, question_id=graphene.String())
def resolve_question(root, 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.
.. code:: python
from graphene import relay
from graphene_django import DjangoObjectType
from .models import Question
class QuestionType(DjangoObjectType):
class Meta:
model = Question
interfaces = (relay.Node,) # make sure you add this
fields = "__all__"
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:
.. code:: python
{
questions (first: 2, after: "YXJyYXljb25uZWN0aW9uOjEwNQ==") {
pageInfo {
startCursor
endCursor
hasNextPage
hasPreviousPage
}
edges {
cursor
node {
id
question_text
}
}
}
}
Which returns:
.. code:: python
{
"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 :code:`pagination` capabilities automatically, adding a :code:`pageInfo` element, and including :code:`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.