OpenAPI

flask-rest-api automatically generates an OpenAPI documentation (formerly known as Swagger) for the API.

That documentation can be made accessible as a JSON file, along with a nice web interface such as ReDoc or Swagger UI.

Specify Versions

The version of the API and the version of the OpenAPI specification can be specified as Flask application parameters:

API_VERSION

Version of the API. It is copied verbatim in the documentation. It should be a string, even it the version is a number.

Default: '1'

OPENAPI_VERSION

Version of the OpenAPI standard used to describe the API. It should be provided as a string.

The OpenAPI version must be passed either as application parameter or at Api initialization in spec_kwargs parameters.

Add Documentation Information to Resources

Add Summary and Description

flask-rest-api uses view functions docstrings to fill the summary and description attributes of an operation object.

def get(...):
    """Find pets by ID

    Return pets based on ID.
    ---
    Internal comment not meant to be exposed.
    """

The part of the docstring following the '---' line is ignored.

The part before the '---' line is used as summary and description. The first lines are used as summary. If an empty line is met, all following lines are used as description.

The example above produces the following documentation attributes:

{
    'get': {
        'summary': 'Find pets by ID',
        'description': 'Return pets based on ID',
    }
}

The delimiter line is the line starting with the delimiter string defined in Blueprint.DOCSTRING_INFO_DELIMITER. This string defaults to "---" and can be customized in a subclass. None means “no delimiter”: the whole docstring is included in the docs.

Document Operations Parameters and Responses

Schemas passed in Blueprint.arguments to deserialize arguments are parsed automatically to generate corresponding documentation. Additional example and examples parameters can be used to provide examples (those are only valid for OpenAPI v3).

Likewise, schemas passed in Blueprint.response to serialize responses are parsed automatically to generate corresponding documentation. Additional example and examples parameters can be used to provide examples (examples is only valid for OpenAPI v3). Additional headers parameters can be used to document response headers.

Document Path Parameters

Path parameters are automatically documented. The type in the documentation is inferred from the path parameter converter used in the URL rule. Custom path parameters should be registered for their type to be correctly determined (see below).

The Blueprint.route method takes a parameters argument to pass documentation for parameters that are shared by all operations of a path. It can be used to pass extra documentation, such as examples, for path parameters.

Pass Extra Documentation Information

flask-rest-api tries to document the API as automatically as possible and to provide explicit means to pass extra-information that can’t be inferred from the code, such as descriptions, examples, etc.

The Blueprint.doc decorator provides a means to pass extra documentation information. It comes in handy if an OpenAPI feature is not supported, but it suffers from a few limitations, and it should be considered a last resort solution until flask-rest-api is improved to fit the need.

Known issues and alternatives are discussed in issue #71.

Populate the Root Document Object

Additional root document attributes can be passed either in the code, in Api parameter spec_kwargs, or as Flask app configuration parameters.

app.config['API_SPEC_OPTIONS'] = {'x-internal-id': '2'}

api = Api(app, spec_kwargs={'host': 'example.com', 'x-internal-id': '1'})

Note that app.config overrides spec_kwargs. The example above produces

{'host': 'example.com', 'x-internal-id': '2', ...}

Note

Again, flask-rest-api tries to provide as much information as possible, but some values can only by provided by the user.

When using OpenAPI v2, basePath is automatically set from the value of the flask parameter APPLICATION_ROOT. In OpenAPI v3, basePath is removed, and the servers attribute can only be set by the user.

Document Top-level Components

Documentation components can be passed by accessing the internal apispec Components object.

 api = Api(app)
 api.spec.components.parameter(
   'Pet name',
   'query',
   {'description': 'Item ID', 'format': 'int32', 'required': True}
)

Register Custom Fields

Standard marshmallow Field classes are documented with the correct type and format.

When using custom fields, the type and format must be passed, either explicitly or by specifying a parent field class, using Api.register_field():

# Map to ('string', 'ObjectId') passing type and format
api.register_field(ObjectId, 'string', 'ObjectId')

# Map to ('string') passing type
api.register_field(CustomString, 'string', None)

# Map to ('integer, 'int32') passing a code marshmallow field
api.register_field(CustomInteger, ma.fields.Integer)

Register Custom Path Parameter Converters

Likewise, standard types used as path parameter converters in the flask routes are correctly documented, but custom path converters must be registered.

The Api.register_converter() allows to register a converter in the Api object to generate an accurate documentation.

# Register MongoDB's ObjectId converter in Flask application
app.url_map.converters['objectid'] = ObjectIdConverter

# Register converter in Api
api.register_converter(ObjectIdConverter, 'string', 'ObjectID')

@blp.route('/pets/{objectid:pet_id}')
    ...

Enforce Order in OpenAPI Specification File

When a Blueprint is registered, a tag is created with the Blueprint name. The display order in the interface is the Blueprint registration order. And the display order inside a tag is the order in which the resources are defined in the Blueprint.

In the OpenAPI specification file, the fields of a Schema are documented as schema properties. Although objects are not ordered in JSON, OpenAPI graphical interfaces tend to respect the order in which the properties are defined in the properties object in the specification file.

When using an ordererd Schema, the fields definition order is preserved when generating the specification file and the properties are displayed in that order.

This is typically done in a base class:

class MyBaseSchema(ma.Schema):
    class Meta:
        ordered = True

class User(MyBaseSchema):
    name = ma.fields.String()
    surname = ma.fields.String()

Passing ordered Meta attribute is not necessary when using a Python version for which dictionaries are always ordered (>= 3.7 or CPython 3.6).

Serve the OpenAPI Documentation

Now that that the documentation is generated, it should be made available to the clients. flask-rest-api can define routes to provide both the documentation as a JSON file and a nice web interface to browse it interactively. This feature is accessible through Flask app parameters.

OPENAPI_URL_PREFIX

Defines the base path for both the JSON file and the UI. If None, the documentation is not served and the following parameters are ignored.

Default: None

OPENAPI_JSON_PATH

Path to the JSON file, relative to the base path.

Default: openapi.json

Both ReDoc and Swagger UI interfaces are available to present the API.

Their configuration logics are similar. If a path is set, then flask-rest-api creates a route in the application to serve the interface page, using the JS script from a user defined URL, if any, or from a CDN URL built with the version number.

OPENAPI_REDOC_PATH

If not None, path to the ReDoc page, relative to the base path.

Default: None

OPENAPI_REDOC_URL

URL to the ReDoc script. If None, a CDN version is used.

Default: None

OPENAPI_REDOC_VERSION

ReDoc version as string. Should be an existing version number, latest (latest 1.x version) or next (latest 2.x version).

This is used to build the CDN URL if OPENAPI_REDOC_URL is None.

On a production instance, it is recommended to specify a fixed version number.

Default: 'latest'

OPENAPI_SWAGGER_UI_PATH

If not None, path to the Swagger UI page, relative to the base path.

Default: None

OPENAPI_SWAGGER_UI_URL

URL to the Swagger UI script. If None, a CDN version is used.

Default: None

OPENAPI_SWAGGER_UI_VERSION

Swagger UI version as string. Contrary to ReDoc, there is no default value pointing to the latest version, so it must be specified.

This is used to build the CDN URL if OPENAPI_SWAGGER_UI_URL is None.

Default: None

OPENAPI_SWAGGER_UI_SUPPORTED_SUBMIT_METHODS

List of methods for which the ‘Try it out!’ feature is enabled. Should be a list of lowercase HTTP methods.

Passing an empty list disables the feature globally.

Default: ['get', 'put', 'post', 'delete', 'options', 'head', 'patch', 'trace']

Warning

The version strings are not checked by flask-rest-api. They are used as is to build the URL pointing to the UI script. Typos won’t be caught.