django-rest-framework/docs/api-guide/schemas.md

source: schemas.py

Schemas

A machine-readable [schema] describes what resources are available via the API, what their URLs are, how they are represented and what operations they support.

— Heroku, JSON Schema for the Heroku Platform API

API schemas are a useful tool that allow for a range of use cases, including generating reference documentation, or driving dynamic client libraries that can interact with your API.

Install Core API

You'll need to install the coreapi package in order to add schema support for REST framework.

pip install coreapi

Internal schema representation

REST framework uses Core API in order to model schema information in a format-independent representation. This information can then be rendered into various different schema formats, or used to generate API documentation.

When using Core API, a schema is represented as a Document which is the top-level container object for information about the API. Available API interactions are represented using Link objects. Each link includes a URL, HTTP method, and may include a list of Field instances, which describe any parameters that may be accepted by the API endpoint. The Link and Field instances may also include descriptions, that allow an API schema to be rendered into user documentation.

Here's an example of an API description that includes a single search endpoint:

coreapi.Document(
    title='Flight Search API',
    url='https://api.example.org/',
    content={
        'search': coreapi.Link(
            url='/search/',
            action='get',
            fields=[
                coreapi.Field(
                    name='from',
                    required=True,
                    location='query',
                    description='City name or airport code.'
                ),
                coreapi.Field(
                    name='to',
                    required=True,
                    location='query',
                    description='City name or airport code.'
                ),
                coreapi.Field(
                    name='date',
                    required=True,
                    location='query',
                    description='Flight date in "YYYY-MM-DD" format.'
                )
            ],
            description='Return flight availability and prices.'
        )
    }
)

Schema output formats

In order to be presented in an HTTP response, the internal representation has to be rendered into the actual bytes that are used in the response.

Core JSON is designed as a canonical format for use with Core API. REST framework includes a renderer class for handling this media type, which is available as renderers.CoreJSONRenderer.

Alternate schema formats

Other schema formats such as Open API ("Swagger"), JSON HyperSchema, or API Blueprint can also be supported by implementing a custom renderer class that handles converting a Document instance into a bytestring representation.

If there is a Core API codec package that supports encoding into the format you want to use then implementing the renderer class can be done by using the codec.

Example

For example, the openapi_codec package provides support for encoding or decoding to the Open API ("Swagger") format:

from rest_framework import renderers
from openapi_codec import OpenAPICodec

class SwaggerRenderer(renderers.BaseRenderer):
    media_type = 'application/openapi+json'
    format = 'swagger'

    def render(self, data, media_type=None, renderer_context=None):
        codec = OpenAPICodec()
        return codec.dump(data)

Schemas vs Hypermedia

It's worth pointing out here that Core API can also be used to model hypermedia responses, which present an alternative interaction style to API schemas.

With an API schema, the entire available interface is presented up-front as a single endpoint. Responses to individual API endpoints are then typically presented as plain data, without any further interactions contained in each response.

With Hypermedia, the client is instead presented with a document containing both data and available interactions. Each interaction results in a new document, detailing both the current state and the available interactions.

Further information and support on building Hypermedia APIs with REST framework is planned for a future version.

---

Creating a schema

REST framework includes functionality for auto-generating a schema, or allows you to specify one explicitly.

Manual Schema Specification

To manually specify a schema you create a Core API Document, similar to the example above.

schema = coreapi.Document(
    title='Flight Search API',
    content={
        ...
    }
)

Automatic Schema Generation

Automatic schema generation is provided by the SchemaGenerator class.

SchemaGenerator processes a list of routed URL pattterns and compiles the appropriately structured Core API Document.

Basic usage is just to provide the title for your schema and call get_schema():

generator = schemas.SchemaGenerator(title='Flight Search API')
schema = generator.get_schema()

Per-View Schema Customisation

By default, view introspection is performed by an AutoSchema instance accessible via the schema attribute on APIView. This provides the appropriate Core API Link object for the view, request method and path:

auto_schema = view.schema
coreapi_link = auto_schema.get_link(...)

(In compiling the schema, SchemaGenerator calls view.schema.get_link() for each view, allowed method and path.)

---

Note: For basic APIView subclasses, default introspection is essentially limited to the URL kwarg path parameters. For GenericAPIView subclasses, which includes all the provided class based views, AutoSchema will attempt to introspect serialiser, pagination and filter fields, as well as provide richer path field descriptions. (The key hooks here are the relevant GenericAPIView attributes and methods: get_serializer, pagination_class, filter_backends and so on.)

---

To customise the Link generation you may:

• Instantiate AutoSchema on your view with the manual_fields kwarg:

    from rest_framework.views import APIView
    from rest_framework.schemas import AutoSchema
  
    class CustomView(APIView):
        ...
        schema = AutoSchema(
            manual_fields=[
                coreapi.Field("extra_field", ...),
            ]
        )
  

  This allows extension for the most common case without subclassing.

• Provide an AutoSchema subclass with more complex customisation:

    from rest_framework.views import APIView
    from rest_framework.schemas import AutoSchema
  
    class CustomSchema(AutoSchema):
        def get_link(...):
            # Implement custom introspection here (or in other sub-methods)
  
    class CustomView(APIView):
        ...
        schema = CustomSchema()
  

  This provides complete control over view introspection.

• Instantiate ManualSchema on your view, providing the Core API Fields for the view explicitly:

    from rest_framework.views import APIView
    from rest_framework.schemas import ManualSchema
  
    class CustomView(APIView):
        ...
        schema = ManualSchema(fields=[
            coreapi.Field(
                "first_field",
                required=True,
                location="path",
                schema=coreschema.String()
            ),
            coreapi.Field(
                "second_field",
                required=True,
                location="path",
                schema=coreschema.String()
            ),
        ])
  

  This allows manually specifying the schema for some views whilst maintaining automatic generation elsewhere.

You may disable schema generation for a view by setting schema to None:

    class CustomView(APIView):
        ...
        schema = None  # Will not appear in schema

---

Note: For full details on SchemaGenerator plus the AutoSchema and ManualSchema descriptors see the API Reference below.

---

Adding a schema view

There are a few different ways to add a schema view to your API, depending on exactly what you need.

The get_schema_view shortcut

The simplest way to include a schema in your project is to use the get_schema_view() function.

from rest_framework.schemas import get_schema_view

schema_view = get_schema_view(title="Server Monitoring API")

urlpatterns = [
    url('^$', schema_view),
    ...
]

Once the view has been added, you'll be able to make API requests to retrieve the auto-generated schema definition.

$ http http://127.0.0.1:8000/ Accept:application/coreapi+json
HTTP/1.0 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/vnd.coreapi+json

{
    "_meta": {
        "title": "Server Monitoring API"
    },
    "_type": "document",
    ...
}

The arguments to get_schema_view() are:

title

May be used to provide a descriptive title for the schema definition.

url

May be used to pass a canonical URL for the schema.

schema_view = get_schema_view(
    title='Server Monitoring API',
    url='https://www.example.org/api/'
)

urlconf

A string representing the import path to the URL conf that you want to generate an API schema for. This defaults to the value of Django's ROOT_URLCONF setting.

schema_view = get_schema_view(
    title='Server Monitoring API',
    url='https://www.example.org/api/',
    urlconf='myproject.urls'
)

renderer_classes

May be used to pass the set of renderer classes that can be used to render the API root endpoint.

from rest_framework.schemas import get_schema_view
from rest_framework.renderers import CoreJSONRenderer
from my_custom_package import APIBlueprintRenderer

schema_view = get_schema_view(
    title='Server Monitoring API',
    url='https://www.example.org/api/',
    renderer_classes=[CoreJSONRenderer, APIBlueprintRenderer]
)

patterns

List of url patterns to limit the schema introspection to. If you only want the myproject.api urls to be exposed in the schema:

schema_url_patterns = [
    url(r'^api/', include('myproject.api.urls')),
]

schema_view = get_schema_view(
    title='Server Monitoring API',
    url='https://www.example.org/api/',
    patterns=schema_url_patterns,
)

generator_class

May be used to specify a SchemaGenerator subclass to be passed to the SchemaView.

authentication_classes

May be used to specify the list of authentication classes that will apply to the schema endpoint. Defaults to settings.DEFAULT_AUTHENTICATION_CLASSES

permission_classes

May be used to specify the list of permission classes that will apply to the schema endpoint. Defaults to settings.DEFAULT_PERMISSION_CLASSES

Using an explicit schema view

If you need a little more control than the get_schema_view() shortcut gives you, then you can use the SchemaGenerator class directly to auto-generate the Document instance, and to return that from a view.

This option gives you the flexibility of setting up the schema endpoint with whatever behaviour you want. For example, you can apply different permission, throttling, or authentication policies to the schema endpoint.

Here's an example of using SchemaGenerator together with a view to return the schema.

views.py:

from rest_framework.decorators import api_view, renderer_classes
from rest_framework import renderers, response, schemas

generator = schemas.SchemaGenerator(title='Bookings API')

@api_view()
@renderer_classes([renderers.CoreJSONRenderer])
def schema_view(request):
    schema = generator.get_schema(request)
    return response.Response(schema)

urls.py:

urlpatterns = [
    url('/', schema_view),
    ...
]

You can also serve different schemas to different users, depending on the permissions they have available. This approach can be used to ensure that unauthenticated requests are presented with a different schema to authenticated requests, or to ensure that different parts of the API are made visible to different users depending on their role.

In order to present a schema with endpoints filtered by user permissions, you need to pass the request argument to the get_schema() method, like so:

@api_view()
@renderer_classes([renderers.CoreJSONRenderer])
def schema_view(request):
    generator = schemas.SchemaGenerator(title='Bookings API')
    return response.Response(generator.get_schema(request=request))

Explicit schema definition

An alternative to the auto-generated approach is to specify the API schema explicitly, by declaring a Document object in your codebase. Doing so is a little more work, but ensures that you have full control over the schema representation.

import coreapi
from rest_framework.decorators import api_view, renderer_classes
from rest_framework import renderers, response

schema = coreapi.Document(
    title='Bookings API',
    content={
        ...
    }
)

@api_view()
@renderer_classes([renderers.CoreJSONRenderer])
def schema_view(request):
    return response.Response(schema)

Static schema file

A final option is to write your API schema as a static file, using one of the available formats, such as Core JSON or Open API.

You could then either:

• Write a schema definition as a static file, and serve the static file directly.
• Write a schema definition that is loaded using Core API, and then rendered to one of many available formats, depending on the client request.

---

Schemas as documentation

One common usage of API schemas is to use them to build documentation pages.

The schema generation in REST framework uses docstrings to automatically populate descriptions in the schema document.

These descriptions will be based on:

• The corresponding method docstring if one exists.
• A named section within the class docstring, which can be either single line or multi-line.
• The class docstring.

Examples

An APIView, with an explicit method docstring.

class ListUsernames(APIView):
    def get(self, request):
        """
        Return a list of all user names in the system.
        """
        usernames = [user.username for user in User.objects.all()]
        return Response(usernames)

A ViewSet, with an explict action docstring.

class ListUsernames(ViewSet):
    def list(self, request):
        """
        Return a list of all user names in the system.
        """
        usernames = [user.username for user in User.objects.all()]
        return Response(usernames)

A generic view with sections in the class docstring, using single-line style.

class UserList(generics.ListCreateAPIView):
    """
    get: List all the users.
    post: Create a new user.
    """
    queryset = User.objects.all()
    serializer_class = UserSerializer
    permission_classes = (IsAdminUser,)

A generic viewset with sections in the class docstring, using multi-line style.

class UserViewSet(viewsets.ModelViewSet):
    """
    API endpoint that allows users to be viewed or edited.

    retrieve:
    Return a user instance.

    list:
    Return all users, ordered by most recently joined.
    """
    queryset = User.objects.all().order_by('-date_joined')
    serializer_class = UserSerializer

---

API Reference

SchemaGenerator

A class that walks a list of routed URL patterns, requests the schema for each view, and collates the resulting CoreAPI Document.

Typically you'll instantiate SchemaGenerator with a single argument, like so:

generator = SchemaGenerator(title='Stock Prices API')

Arguments:

• title required - The name of the API.
• url - The root URL of the API schema. This option is not required unless the schema is included under path prefix.
• patterns - A list of URLs to inspect when generating the schema. Defaults to the project's URL conf.
• urlconf - A URL conf module name to use when generating the schema. Defaults to settings.ROOT_URLCONF.

get_schema(self, request)

Returns a coreapi.Document instance that represents the API schema.

@api_view
@renderer_classes([renderers.CoreJSONRenderer])
def schema_view(request):
    generator = schemas.SchemaGenerator(title='Bookings API')
    return Response(generator.get_schema())

The request argument is optional, and may be used if you want to apply per-user permissions to the resulting schema generation.

get_links(self, request)

Return a nested dictionary containing all the links that should be included in the API schema.

This is a good point to override if you want to modify the resulting structure of the generated schema, as you can build a new dictionary with a different layout.

AutoSchema

A class that deals with introspection of individual views for schema generation.

AutoSchema is attached to APIView via the schema attribute.

The AutoSchema constructor takes a single keyword argument manual_fields.

manual_fields: a list of coreapi.Field instances that will be added to the generated fields. Generated fields with a matching name will be overwritten.

class CustomView(APIView):
    schema = AutoSchema(manual_fields=[
        coreapi.Field(
            "my_extra_field",
            required=True,
            location="path",
            schema=coreschema.String()
        ),
    ])

For more advanced customisation subclass AutoSchema to customise schema generation.

class CustomViewSchema(AutoSchema):
    """
    Overrides `get_link()` to provide Custom Behavior X
    """

    def get_link(self, path, method, base_url):
        link = super().get_link(path, method, base_url)
        # Do something to customize link here...
        return link

class MyView(APIView):
  schema = CustomViewSchema()

The following methods are available to override.

get_link(self, path, method, base_url)

Returns a coreapi.Link instance corresponding to the given view.

This is the main entry point. You can override this if you need to provide custom behaviors for particular views.

get_description(self, path, method)

Returns a string to use as the link description. By default this is based on the view docstring as described in the "Schemas as Documentation" section above.

get_encoding(self, path, method)

Returns a string to indicate the encoding for any request body, when interacting with the given view. Eg. 'application/json'. May return a blank string for views that do not expect a request body.

get_path_fields(self, path, method):

Return a list of coreapi.Link() instances. One for each path parameter in the URL.

get_serializer_fields(self, path, method)

Return a list of coreapi.Link() instances. One for each field in the serializer class used by the view.

get_pagination_fields(self, path, method)

Return a list of coreapi.Link() instances, as returned by the get_schema_fields() method on any pagination class used by the view.

get_filter_fields(self, path, method)

Return a list of coreapi.Link() instances, as returned by the get_schema_fields() method of any filter classes used by the view.

get_manual_fields(self, path, method)

Return a list of coreapi.Field() instances to be added to or replace generated fields. Defaults to (optional) manual_fields passed to AutoSchema constructor.

May be overridden to customise manual fields by path or method. For example, a per-method adjustment may look like this:

def get_manual_fields(self, path, method):
    """Example adding per-method fields."""

    extra_fields = []
    if method=='GET':
        extra_fields = # ... list of extra fields for GET ...
    if method=='POST':
        extra_fields = # ... list of extra fields for POST ...

    manual_fields = super().get_manual_fields()
    return manual_fields + extra_fields

update_fields(fields, update_with)

Utility staticmethod. Encapsulates logic to add or replace fields from a list by Field.name. May be overridden to adjust replacement criteria.

ManualSchema

Allows manually providing a list of coreapi.Field instances for the schema, plus an optional description.

class MyView(APIView):
  schema = ManualSchema(fields=[
        coreapi.Field(
            "first_field",
            required=True,
            location="path",
            schema=coreschema.String()
        ),
        coreapi.Field(
            "second_field",
            required=True,
            location="path",
            schema=coreschema.String()
        ),
    ]
  )

The ManualSchema constructor takes two arguments:

fields: A list of coreapi.Field instances. Required.

description: A string description. Optional.

---

Core API

This documentation gives a brief overview of the components within the coreapi package that are used to represent an API schema.

Note that these classes are imported from the coreapi package, rather than from the rest_framework package.

Document

Represents a container for the API schema.

title

A name for the API.

url

A canonical URL for the API.

content

A dictionary, containing the Link objects that the schema contains.

In order to provide more structure to the schema, the content dictionary may be nested, typically to a second level. For example:

content={
    "bookings": {
        "list": Link(...),
        "create": Link(...),
        ...
    },
    "venues": {
        "list": Link(...),
        ...
    },
    ...
}

Link

Represents an individual API endpoint.

url

The URL of the endpoint. May be a URI template, such as /users/{username}/.

action

The HTTP method associated with the endpoint. Note that URLs that support more than one HTTP method, should correspond to a single Link for each.

fields

A list of Field instances, describing the available parameters on the input.

description

A short description of the meaning and intended usage of the endpoint.

Field

Represents a single input parameter on a given API endpoint.

name

A descriptive name for the input.

required

A boolean, indicated if the client is required to included a value, or if the parameter can be omitted.

location

Determines how the information is encoded into the request. Should be one of the following strings:

"path"

Included in a templated URI. For example a url value of /products/{product_code}/ could be used together with a "path" field, to handle API inputs in a URL path such as /products/slim-fit-jeans/.

These fields will normally correspond with named arguments in the project URL conf.

"query"

Included as a URL query parameter. For example ?search=sale. Typically for GET requests.

These fields will normally correspond with pagination and filtering controls on a view.

"form"

Included in the request body, as a single item of a JSON object or HTML form. For example {"colour": "blue", ...}. Typically for POST, PUT and PATCH requests. Multiple "form" fields may be included on a single link.

These fields will normally correspond with serializer fields on a view.

"body"

Included as the complete request body. Typically for POST, PUT and PATCH requests. No more than one "body" field may exist on a link. May not be used together with "form" fields.

These fields will normally correspond with views that use ListSerializer to validate the request input, or with file upload views.

encoding

"application/json"

JSON encoded request content. Corresponds to views using JSONParser. Valid only if either one or more location="form" fields, or a single location="body" field is included on the Link.

"multipart/form-data"

Multipart encoded request content. Corresponds to views using MultiPartParser. Valid only if one or more location="form" fields is included on the Link.

"application/x-www-form-urlencoded"

URL encoded request content. Corresponds to views using FormParser. Valid only if one or more location="form" fields is included on the Link.

"application/octet-stream"

Binary upload request content. Corresponds to views using FileUploadParser. Valid only if a location="body" field is included on the Link.

description

A short description of the meaning and intended usage of the input field.

---

Third party packages

drf-yasg - Yet Another Swagger Generator

drf-yasg generates OpenAPI documents suitable for code generation - nested schemas, named models, response bodies, enum/pattern/min/max validators, form parameters, etc.

DRF OpenAPI

DRF OpenAPI renders the schema generated by Django Rest Framework in OpenAPI format.