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04fe299a6e
* Corrected typos in docs/queries.rst. * Add basic resolvers to Relay Full example in docs/queries.rst. Added basic resolvers to Full example in Relay section. * Remove question and question resolver. * Add query example to queries.rst. Added query example in Relay section. Minor clean-up.
333 lines
8.6 KiB
ReStructuredText
333 lines
8.6 KiB
ReStructuredText
Queries & ObjectTypes
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=====================
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Introduction
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------------
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Graphene-Django offers a host of features for performing GraphQL queries.
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Graphene-Django ships with a special ``DjangoObjectType`` that automatically transforms a Django Model
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into a ``ObjectType`` for you.
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Full example
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~~~~~~~~~~~~
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.. code:: python
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# my_app/schema.py
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import graphene
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from graphene_django.types import DjangoObjectType
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from .models import Question
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class QuestionType(DjangoObjectType):
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class Meta:
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model = Question
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class Query:
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questions = graphene.List(QuestionType)
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question = graphene.Field(QuestionType, question_id=graphene.String())
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def resolve_questions(self, info, **kwargs):
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# Querying a list
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return Question.objects.all()
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def resolve_question(self, info, question_id):
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# Querying a single question
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return Question.objects.get(pk=question_id)
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Fields
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------
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By default, ``DjangoObjectType`` will present all fields on a Model through GraphQL.
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If you don't want to do this you can change this by setting either ``only_fields`` and ``exclude_fields``.
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only_fields
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~~~~~~~~~~~
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Show **only** these fields on the model:
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.. code:: python
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class QuestionType(DjangoObjectType):
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class Meta:
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model = Question
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only_fields = ('question_text')
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exclude_fields
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~~~~~~~~~~~~~~
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Show all fields **except** those in ``exclude_fields``:
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.. code:: python
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class QuestionType(DjangoObjectType):
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class Meta:
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model = Question
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exclude_fields = ('question_text')
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Customised fields
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~~~~~~~~~~~~~~~~~
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You can completely overwrite a field, or add new fields, to a ``DjangoObjectType`` using a Resolver:
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.. code:: python
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class QuestionType(DjangoObjectType):
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class Meta:
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model = Question
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exclude_fields = ('question_text')
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extra_field = graphene.String()
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def resolve_extra_field(self, info):
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return 'hello!'
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Related models
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--------------
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Say you have the following models:
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.. code:: python
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class Category(models.Model):
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foo = models.CharField(max_length=256)
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class Question(models.Model):
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category = models.ForeignKey(Category, on_delete=models.CASCADE)
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When ``Question`` is published as a ``DjangoObjectType`` and you want to add ``Category`` as a query-able field like so:
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.. code:: python
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class QuestionType(DjangoObjectType):
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class Meta:
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model = Question
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only_fields = ('category',)
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Then all query-able related models must be defined as DjangoObjectType subclass,
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or they will fail to show if you are trying to query those relation fields. You only
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need to create the most basic class for this to work:
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.. code:: python
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class CategoryType(DjangoObjectType):
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class Meta:
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model = Category
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Default QuerySet
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-----------------
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If you are using ``DjangoObjectType`` you can define a custom `get_queryset` method.
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Use this to control filtering on the ObjectType level instead of the Query object level.
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.. code:: python
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from graphene_django.types import DjangoObjectType
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from .models import Question
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class QuestionType(DjangoObjectType):
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class Meta:
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model = Question
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@classmethod
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def get_queryset(cls, queryset, info):
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if info.context.user.is_anonymous:
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return queryset.filter(published=True)
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return queryset
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Resolvers
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---------
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When a GraphQL query is received by the ``Schema`` object, it will map it to a "Resolver" related to it.
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This resolve method should follow this format:
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.. code:: python
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def resolve_foo(self, info, **kwargs):
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Where "foo" is the name of the field declared in the ``Query`` object.
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.. code:: python
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class Query:
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foo = graphene.List(QuestionType)
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def resolve_foo(self, info, **kwargs):
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id = kwargs.get('id')
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return QuestionModel.objects.get(id)
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Arguments
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~~~~~~~~~
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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.
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.. code:: python
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class Query:
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question = graphene.Field(Question, foo=graphene.String(), bar=graphene.Int())
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def resolve_question(self, info, foo, bar):
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# If `foo` or `bar` are declared in the GraphQL query they will be here, else None.
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return Question.objects.filter(foo=foo, bar=bar).first()
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Info
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~~~~
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The ``info`` argument passed to all resolve methods holds some useful information.
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For Graphene-Django, the ``info.context`` attribute is the ``HTTPRequest`` object
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that would be familiar to any Django developer. This gives you the full functionality
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of Django's ``HTTPRequest`` in your resolve methods, such as checking for authenticated users:
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.. code:: python
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def resolve_questions(self, info, **kwargs):
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# See if a user is authenticated
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if info.context.user.is_authenticated():
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return Question.objects.all()
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else:
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return Question.objects.none()
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Plain ObjectTypes
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-----------------
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With Graphene-Django you are not limited to just Django Models - you can use the standard
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``ObjectType`` to create custom fields or to provide an abstraction between your internal
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Django models and your external API.
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.. code:: python
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import graphene
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from .models import Question
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class MyQuestion(graphene.ObjectType):
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text = graphene.String()
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class Query:
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question = graphene.Field(MyQuestion, question_id=graphene.String())
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def resolve_question(self, info, question_id):
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question = Question.objects.get(pk=question_id)
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return MyQuestion(
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text=question.question_text
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)
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For more information and more examples, please see the `core object type documentation <https://docs.graphene-python.org/en/latest/types/objecttypes/>`__.
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Relay
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-----
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`Relay <http://docs.graphene-python.org/en/latest/relay/>`__ with Graphene-Django gives us some additional features:
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- Pagination and slicing.
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- An abstract ``id`` value which contains enough info for the server to know its type and its id.
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There is one additional import and a single line of code needed to adopt this:
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Full example
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~~~~~~~~~~~~
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See the `Relay documentation <https://docs.graphene-python.org/en/latest/relay/nodes/>`__ on
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the core graphene pages for more information on customizing the Relay experience.
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.. code:: python
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from graphene import relay
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from graphene_django import DjangoObjectType
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from .models import Question
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class QuestionType(DjangoObjectType):
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class Meta:
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model = Question
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interfaces = (relay.Node,)
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class QuestionConnection(relay.Connection):
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class Meta:
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node = QuestionType
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class Query:
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questions = relay.ConnectionField(QuestionConnection)
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def resolve_questions(root, info, **kwargs):
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return Question.objects.all()
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You can now execute queries like:
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.. code:: python
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{
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questions (first: 2, after: "YXJyYXljb25uZWN0aW9uOjEwNQ==") {
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pageInfo {
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startCursor
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endCursor
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hasNextPage
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hasPreviousPage
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}
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edges {
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cursor
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node {
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id
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question_text
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}
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}
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}
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}
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Which returns:
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.. code:: python
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{
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"data": {
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"questions": {
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"pageInfo": {
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"startCursor": "YXJyYXljb25uZWN0aW9uOjEwNg==",
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"endCursor": "YXJyYXljb25uZWN0aW9uOjEwNw==",
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"hasNextPage": true,
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"hasPreviousPage": false
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},
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"edges": [
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{
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"cursor": "YXJyYXljb25uZWN0aW9uOjEwNg==",
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"node": {
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"id": "UGxhY2VUeXBlOjEwNw==",
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"question_text": "How did we get here?"
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}
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},
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{
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"cursor": "YXJyYXljb25uZWN0aW9uOjEwNw==",
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"node": {
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"id": "UGxhY2VUeXBlOjEwOA==",
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"name": "Where are we?"
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}
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}
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]
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}
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}
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}
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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.
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To learn more about Pagination in general, take a look at `Pagination <https://graphql.org/learn/pagination/>`__ on the GraphQL community site.
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