graph-wrap 0.0.2

Extend an existing tastypie REST-based API with a GraphQL interface with a only a couple of lines of code.

GraphWrap

GraphWrap is a python library which, by adding only a couple of lines of code to your django project, can extend an existing django-tastypie REST-based API with a GraphQL interface. This is achieved by leveraging Graphene-Django to dynamically build, at runtime, a GraphQL ObjectType for each tastypie resource. These ObjectTypes are then pieced together to form a GraphQL schema which has the same "shape" as your existing REST API. Note that GraphWrap is not designed to build a GraphQL schema to replace your existing REST API, but rather extend it to offer an additional GraphQL-queryable interface.

Highlights:

• The dynamic nature of the build of the GraphQL layer means that you can continue to develop your existing REST based API and know that the graphql schema will be kept up-to-date automatically.

• Since the graphql layer is using the REST API under-the-hood, you can be sure that important things like serialization (including any custom dehydration), authentication and authorization will be consistent between a REST resource and the corresponding GraphQL type.

• No longer will you be required to hardcode full=True to any of your tastypie resource fields - the client can simply make use of the GraphQL layer to retrieve data from related resources. This can lead to significant performance boosts in certain circumstances (One of the advantages of GraphQL queries is that they solve the n+1 problem which occurs with traditional REST-based APIs.)

Limitations

Here are a couple of limitations of the GraphQL API produced by GraphWrap:

• It can only accept GraphQL queries - mutations and subscriptions are not (yet) supported.

• The schema is built only from tastypie resources which inherit directly from ModelResource - non-ORM based resources are not (yet) supported.

Future Directions

The long term goal for this project is to give the ability to add automatic GraphQL query support to any Django view based REST framework.

Quickstart

Core Requirements

• graphene-django==2.13.0

• django-tastypie>=0.14.0

Each of the above requirements can be run using Python >=2.7 and Django >=1.11.

Installing

pip install graph_wrap

Registering the GraphQL resource

GraphWrap exposes the GraphQL schema via a tastypie resource GraphQLResource (which is effectively a Django class-based view). As with all resources, we are required to register GraphQLResource with the tastypie Api instance before we can interact with it via HTTP requests. Once registered, GraphQLResource builds and exposes a GraphQL queryable schema via the /graphql endpoint.

# tests.urls.py
from graph_wrap import GraphQLResource  # add this line to your project

api = Api('v1')
api.register(GraphQLResource()) # add this line to your project

urlpatterns = [
    path(r'', include(api.urls)),
    ...
]

Querying the GraphQL resource

As mentioned above, GraphWrap exposes the GraphQL API via the /graphql URL.

Settings

In order for GraphQL to be able to build the GraphQL schema from the tastypie Api instance, it needs to know where that instance lives in your project. To allow GraphWrap to locate the Api instance, we can simply add the full path of the instance to our django settings module. For example:

# tests.settings.py

TASTYPIE_API_PATH = 'tests.urls.api'

Documentation (by Example)

In this section we give a brief overview of how to use GraphWrap via examining a simple concrete example.

Set-up

Suppose we have the following basic django models and corresponding tastypie resources ( a fully executable version of this example can be found in graph_wrap.tests):

# models.py

class Author(models.Model):
    name = models.TextField()
    age = models.TextField()


class Post(models.Model):
    content = models.TextField()
    date = models.DateTimeField()
    author = models.ForeignKey(Author, null=True, on_delete=models.SET_NULL)
    files = models.ManyToManyField('Media')


class Media(models.Model):
    name = models.TextField()
    content_type = models.TextField()
    size = models.BigIntegerField()


# api.py

class AuthorResource(ModelResource):
    posts = fields.ManyToManyField('tests.api.PostResource', attribute='post_set')

    class Meta:
        queryset = Author.objects.all()
        resource_name = 'author'
        filtering = {
            'age': ('exact',),
            'name': ('exact',),
        }


class PostResource(ModelResource):
    author = fields.ForeignKey(AuthorResource, attribute='author', null=True)
    files = fields.ManyToManyField('tests.api.MediaResource', attribute='files')
    date = fields.DateTimeField('date')

    class Meta:
        queryset = Post.objects.all()
        resource_name = 'post'


class MediaResource(ModelResource):
    class Meta:
        queryset = Media.objects.all()
        resource_name = 'media'

If we wish to layer our REST resources with a GraphQL interface, we can follow the instructions above in the "Quickstart" guide. Start by registering our GraphQLResource with the tastypie Api instance:

# urls.py

from django.contrib import admin
from django.urls import path, include
from tastypie.api import Api

from graph_wrap import GraphQLResource
from tests.api import AuthorResource, PostResource, MediaResource


api = Api('v1')
api.register(AuthorResource())
api.register(PostResource())
api.register(MediaResource())
api.register(GraphQLResource())

urlpatterns = [
    path(r'', include(api.urls)),
    path('admin/', admin.site.urls),
]

Next, add the TASTYPIE_API_PATH to the django settings module so GraphWrap can locate the tastypie Api:

TASTYPIE_API_PATH = 'tests.urls.api'

Understanding the Schema

With these simple changes, we can now query the /grahql endpoint with GraphQL queries. The structure queries can take, as with all GraphQL APIs, is dictated by the shape of the underlying schema (which, in this case, is dictated by the shape of the tastypie API). To see what the schema looks like, run the following:

>>> from graph_wrap import schema
>>> schema = schema()
>>> print(schema)


schema {
  query: Query
}
type Query {
  author(id: Int!): author_type
  all_authors(orm_filters: String): [author_type]
  post(id: Int!): post_type
  all_posts(orm_filters: String): [post_type]
  media(id: Int!): media_type
  all_medias(orm_filters: String): [media_type]
}
type author_type {
  resource_uri: String!
  posts: [post_type]!
  id: Int!
  name: String!
  age: String!
}
type media_type {
  resource_uri: String!
  id: Int!
  name: String!
  content_type: String!
  size: Int!
}
type post_type {
  resource_uri: String!
  author: author_type
  files: [media_type]!
  date: String!
  id: Int!
  content: String!
}

Important points to note about the schema produced by GraphWrap:

• snake_case: As can be seen above, GraphWrap produces a schema in the snake_case convention. Whilst this is generally not favoured in GraphQL circles, it was chosen here as it would likely be more consistent with the field names on the underlying REST resources (which would use most often use the PEP8 recommended snake case convention).

• Root Query field names: For each REST model-resource, GraphWrap adds to the Query type precisely two fields - one corresponding to the data accessible via a GET request to the 'list' endpoint of the resource, and one corresponding to the data accessible via a GET request to the 'detail' endpoint of the resource. If we take our AuthorResource as an example:

  • the 'list' endpoint corresponds to the url /author. This maps to the all_authors field on the Query type.
  • the 'detail' endpoint corresponds to urls of the form '/author/{author_pk}'. This maps to the author(id: Int!) field on the Query type (where, in the usual GraphQL schema syntax, (id: Int!) indicates that an integer author id must be supplied.)

• ObjectType and ObjectType Field names:

  • GraphWrap maps each model-resource maps to a GraphQL ObjectType. The name of the resultant ObjectType can be found by appending _type to the name of the corresponding resource. For example, the AuthorResource, which has name author, maps to the author_type GraphQL ObjectType.
  • The names of the fields on each ObjectType match those of the names of the fields on the corresponding resource.

• Filtering (orm_filters): Notice in the schema above that each all_ field can be queried with an optional orm_filters argument. This is the GraphQL equivalent of the ORM filtering offered by tastypie on list endpoints. If we take our AuthorResource as an example (which has been defined with filtering = {'age': ('exact',), 'name': ('exact',)}), then the REST GET query /author/?name=Paul can be achieved via a POST request to /graphql with the following query:

  {
    all_authors(orm_filters: "name=Paul") {
      name
    }
  }
  

Authentication and Authorization of GraphQLResource

The authentication/authorization applied when querying /graphql is the authentication/authorization defined on the resource corresponding to the root field of the query applied. This is consistent with the way tastypie handles authenticaiton/authorization. So, for example, the following query would invoke whatever authentication/authorization was defined on the AuthorResource:

    {
      all_authors(orm_filters: "name=Paul") {
        name
      }
    }

Making Queries: REST vs GraphQL

In this section we'll look at how various REST GET requests can be mapped to queries for the /graphql endpoint. Again, we'll do this via examining our explicit concrete example (note that the queries and requests pictured in this section were produced on the Insomnia HTTP client, which has a integration with GraphQL):

'list' endpoint requests

• REST:

• GraphQL

'detail' endpoint requests

• REST

• GraphQL

Filtering

• REST

• GraphQL

Some fancier GraphQL query examples - see GraphQL queries for more

• Nesting

• Fragments