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Queries
About the Django structure
It’s important to understand how the Django project structure works before moving on.
In the last chapter, you created a Django Project, which holds everything related to your application. However, Django separates the project into apps. Think about apps as a separation of concerns. You will have two apps, one for Users and one for the Links.
Another essential decision is about the database. Django works out of the box with SQLite – a file based database – which you will use. On production systems, you should have a more robust database, such as PostgreSQL.
Creating the Links app
In the project’s root (next to the manage.py file), create the links app:
python manage.py startapp links
It will create the links app and some default files inside it.
With an app in place, you need to define a Model – the layer between Django and the database.
In the links/models.py file, add the following content:
.../graphql-python/hackernews/links/models.py
class Link(models.Model):
url = models.URLField()
description = models.TextField(blank=True)
Lastly, configure Django to use the new links app in the hackernews/settings.py file:
.../graphql-python/hackernews/hackernews/settings.py
INSTALLED_APPS = (
# After the graphene_django app
'links',
)
Create the database tables:
python manage.py makemigrations
python manage.py migrate
Enter the Django shell with the command python manage.py shell and create some links:
from links.models import Link
Link.objects.create(url='https://www.howtographql.com/', description='The Fullstack Tutorial for GraphQL')
Link.objects.create(url='https://twitter.com/jonatasbaldin/', description='The Jonatas Baldin Twitter')
Creating your first Type and Schema
In GraphQL, a Type is an object that may contain multiple fields. Each field is calculated through resolvers, that returns a value. A collection of types is called a schema. Every schema has a special type called query for getting data from the server and mutation for sending data to the server.
This is a simple overview of the concepts, but it should be enough to go through the tutorial. You can read more about it here.
Create the links/schema.py file, with the content below:
.../graphql-python/hackernews/links/schema.py
import graphene
from graphene_django import DjangoObjectType
from .models import Link
class LinkType(DjangoObjectType):
class Meta:
model = Link
class Query(graphene.ObjectType):
links = graphene.List(LinkType)
def resolve_links(self, info, **kwargs):
return Link.objects.all()
In the snippet above, the LinkType was created using the DjangoObjectType – a custom type available in Graphene Django. Also, the special type query was created with a resolver for the field links, which returns all the links.
Create the hackernews/schema.py file, with the query type:
.../graphql-python/hackernews/hackernews/schema.py
import graphene
import links.schema
class Query(links.schema.Query, graphene.ObjectType):
pass
schema = graphene.Schema(query=Query)
Why creating another query? This query just inherits the query defined before. This way, you are able to keep every part of the schema isolated in the apps.
Wow, that’s a lot, right? But now you can finally query some data!
Introducing GraphiQL
GraphiQL is a graphical interactive in-browser GraphQL IDE. In other words, a playground. Note that you need to disable the Django CSRF protection.
To install it, add the following in the hackernews/urls.py file:
.../graphql-python/hackernews/hackernews/urls.py
... # code
from django.views.decorators.csrf import csrf_exempt
from graphene_django.views import GraphQLView
urlpatterns = [
path('admin/', admin.site.urls),
path('graphql/', csrf_exempt(GraphQLView.as_view(graphiql=True))),
]
Open your browser and access http://localhost:8000/graphql/, you should see a screen like this:
On the right there’s the Documentation Explorer, information about our schema created automatically through introspection. On the left, to create your first query, typing the following:
query {
links {
id
description
url
}
}You should see a response link this:
Congratulations! Play around a little bit, try to remove some fields or add others. Break it! It’s the best way of learning!
Unlock the next chapter
In GraphQL, what type of method returns the value of a field?
Query
Mutation
Type
Resolver
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