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Schema

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.

Django REST Framework provides support for automatic generation of OpenAPI schemas.

Overview

Schema generation has several moving parts. It's worth having an overview:

  • SchemaGenerator is a top-level class that is responsible for walking your configured URL patterns, finding APIView subclasses, enquiring for their schema representation, and compiling the final schema object.
  • AutoSchema encapsulates all the details necessary for per-view schema introspection. Is attached to each view via the schema attribute. You subclass AutoSchema in order to customize your schema.
  • The generateschema management command allows you to generate a static schema offline.
  • Alternatively, you can route SchemaView to dynamically generate and serve your schema.
  • settings.DEFAULT_SCHEMA_CLASS allows you to specify an AutoSchema subclass to serve as your project's default.

The following sections explain more.

Generating an OpenAPI Schema

Install dependencies

pip install pyyaml uritemplate
  • pyyaml is used to generate schema into YAML-based OpenAPI format.
  • uritemplate is used internally to get parameters in path.

Generating a static schema with the generateschema management command

If your schema is static, you can use the generateschema management command:

./manage.py generateschema --file openapi-schema.yml

Once you've generated a schema in this way you can annotate it with any additional information that cannot be automatically inferred by the schema generator.

You might want to check your API schema into version control and update it with each new release, or serve the API schema from your site's static media.

Generating a dynamic schema with SchemaView

If you require a dynamic schema, because foreign key choices depend on database values, for example, you can route a SchemaView that will generate and serve your schema on demand.

To route a SchemaView, use the get_schema_view() helper.

In urls.py:

from rest_framework.schemas import get_schema_view

urlpatterns = [
    # ...
    # Use the `get_schema_view()` helper to add a `SchemaView` to project URLs.
    #   * `title` and `description` parameters are passed to `SchemaGenerator`.
    #   * Provide view name for use with `reverse()`.
    path('openapi', get_schema_view(
        title="Your Project",
        description="API for all things …",
        version="1.0.0"
    ), name='openapi-schema'),
    # ...
]

get_schema_view()

The get_schema_view() helper takes the following keyword arguments:

  • title: May be used to provide a descriptive title for the schema definition.
  • description: Longer descriptive text.
  • version: The version of the API.

  • url: May be used to pass a canonical base 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'
)

  • 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 = [
    path('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.
  • renderer_classes: May be used to pass the set of renderer classes that can be used to render the API root endpoint.

SchemaGenerator

Schema-level customization

from rest_framework.schemas.openapi import SchemaGenerator

SchemaGenerator is a class that walks a list of routed URL patterns, requests the schema for each view and collates the resulting OpenAPI schema.

Typically you won't need to instantiate SchemaGenerator yourself, but you can do so like so:

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

Arguments:

  • title required: The name of the API.
  • description: Longer descriptive text.
  • version: The version of the API. Defaults to 0.1.0.
  • 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.

In order to customize the top-level schema, subclass rest_framework.schemas.openapi.SchemaGenerator and provide your subclass as an argument to the generateschema command or get_schema_view() helper function.

get_schema(self, request)

Returns a dictionary that represents the OpenAPI schema:

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

This is a good point to override if you want to customize the generated dictionary For example you might wish to add terms of service to the top-level info object:

class TOSSchemaGenerator(SchemaGenerator):
    def get_schema(self, *args, **kwargs):
        schema = super().get_schema(*args, **kwargs)
        schema["info"]["termsOfService"] = "https://example.com/tos.html"
        return schema

AutoSchema

Per-View Customization

from rest_framework.schemas.openapi import AutoSchema

By default, view introspection is performed by an AutoSchema instance accessible via the schema attribute on APIView.

auto_schema = some_view.schema

AutoSchema provides the OpenAPI elements needed for each view, request method and path:

  • A list of OpenAPI components. In DRF terms these are mappings of serializers that describe request and response bodies.
  • The appropriate OpenAPI operation object that describes the endpoint, including path and query parameters for pagination, filtering, and so on.
components = auto_schema.get_components(...)
operation = auto_schema.get_operation(...)

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

Note: The automatic introspection of components, and many operation parameters relies on the relevant attributes and methods of GenericAPIView: get_serializer(), pagination_class, filter_backends, etc. For basic APIView subclasses, default introspection is essentially limited to the URL kwarg path parameters for this reason.

AutoSchema encapsulates the view introspection needed for schema generation. Because of this all the schema generation logic is kept in a single place, rather than being spread around the already extensive view, serializer and field APIs.

Keeping with this pattern, try not to let schema logic leak into your own views, serializers, or fields when customizing the schema generation. You might be tempted to do something like this:

class CustomSchema(AutoSchema):
    """
    AutoSchema subclass using schema_extra_info on the view.
    """
    ...

class CustomView(APIView):
    schema = CustomSchema()
    schema_extra_info = ... some extra info ...

Here, the AutoSchema subclass goes looking for schema_extra_info on the view. This is OK (it doesn't actually hurt) but it means you'll end up with your schema logic spread out in a number of different places.

Instead try to subclass AutoSchema such that the extra_info doesn't leak out into the view:

class BaseSchema(AutoSchema):
    """
    AutoSchema subclass that knows how to use extra_info.
    """
    ...

class CustomSchema(BaseSchema):
    extra_info = ... some extra info ...

class CustomView(APIView):
    schema = CustomSchema()

This style is slightly more verbose but maintains the encapsulation of the schema related code. It's more cohesive in the parlance. It'll keep the rest of your API code more tidy.

If an option applies to many view classes, rather than creating a specific subclass per-view, you may find it more convenient to allow specifying the option as an __init__() kwarg to your base AutoSchema subclass:

class CustomSchema(BaseSchema):
    def __init__(self, **kwargs):
        # store extra_info for later
        self.extra_info = kwargs.pop("extra_info")
        super().__init__(**kwargs)

class CustomView(APIView):
    schema = CustomSchema(
        extra_info=... some extra info ...
    )

This saves you having to create a custom subclass per-view for a commonly used option.

Not all AutoSchema methods expose related __init__() kwargs, but those for the more commonly needed options do.

AutoSchema methods

get_components()

Generates the OpenAPI components that describe request and response bodies, deriving their properties from the serializer.

Returns a dictionary mapping the component name to the generated representation. By default this has just a single pair but you may override get_components() to return multiple pairs if your view uses multiple serializers.

get_component_name()

Computes the component's name from the serializer.

You may see warnings if your API has duplicate component names. If so you can override get_component_name() or pass the component_name __init__() kwarg (see below) to provide different names.

map_serializer()

Maps serializers to their OpenAPI representations.

Most serializers should conform to the standard OpenAPI object type, but you may wish to override map_serializer() in order to customize this or other serializer-level fields.

map_field()

Maps individual serializer fields to their schema representation. The base implementation will handle the default fields that Django REST Framework provides.

For SerializerMethodField instances, for which the schema is unknown, or custom field subclasses you should override map_field() to generate the correct schema:

class CustomSchema(AutoSchema):
    """Extension of ``AutoSchema`` to add support for custom field schemas."""

    def map_field(self, field):
        # Handle SerializerMethodFields or custom fields here...
        # ...
        return super().map_field(field)

Authors of third-party packages should aim to provide an AutoSchema subclass, and a mixin, overriding map_field() so that users can easily generate schemas for their custom fields.

get_tags()

OpenAPI groups operations by tags. By default tags taken from the first path segment of the routed URL. For example, a URL like /users/{id}/ will generate the tag users.

You can pass an __init__() kwarg to manually specify tags (see below), or override get_tags() to provide custom logic.

get_operation()

Returns the OpenAPI operation object that describes the endpoint, including path and query parameters for pagination, filtering, and so on.

Together with get_components(), this is the main entry point to the view introspection.

get_operation_id()

There must be a unique operationid for each operation. By default the operationId is deduced from the model name, serializer name or view name. The operationId looks like "listItems", "retrieveItem", "updateItem", etc. The operationId is camelCase by convention.

get_operation_id_base()

If you have several views with the same model name, you may see duplicate operationIds.

In order to work around this, you can override get_operation_id_base() to provide a different base for name part of the ID.

get_serializer()

If the view has implemented get_serializer(), returns the result.

get_request_serializer()

By default returns get_serializer() but can be overridden to differentiate between request and response objects.

get_response_serializer()

By default returns get_serializer() but can be overridden to differentiate between request and response objects.

AutoSchema.__init__() kwargs

AutoSchema provides a number of __init__() kwargs that can be used for common customizations, if the default generated values are not appropriate.

The available kwargs are:

  • tags: Specify a list of tags.
  • component_name: Specify the component name.
  • operation_id_base: Specify the resource-name part of operation IDs.

You pass the kwargs when declaring the AutoSchema instance on your view:

class PetDetailView(generics.RetrieveUpdateDestroyAPIView):
    schema = AutoSchema(
        tags=['Pets'],
        component_name='Pet',
        operation_id_base='Pet',
    )
    ...

Assuming a Pet model and PetSerializer serializer, the kwargs in this example are probably not needed. Often, though, you'll need to pass the kwargs if you have multiple view targeting the same model, or have multiple views with identically named serializers.

If your views have related customizations that are needed frequently, you can create a base AutoSchema subclass for your project that takes additional __init__() kwargs to save subclassing AutoSchema for each view.