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125 lines
4.6 KiB
Markdown
125 lines
4.6 KiB
Markdown
---
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source:
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- metadata.py
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---
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# Metadata
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> [The `OPTIONS`] method allows a client to determine the options and/or requirements associated with a resource, or the capabilities of a server, without implying a resource action or initiating a resource retrieval.
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>
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> — [RFC7231, Section 4.3.7.][cite]
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REST framework includes a configurable mechanism for determining how your API should respond to `OPTIONS` requests. This allows you to return API schema or other resource information.
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There are not currently any widely adopted conventions for exactly what style of response should be returned for HTTP `OPTIONS` requests, so we provide an ad-hoc style that returns some useful information.
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Here's an example response that demonstrates the information that is returned by default.
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HTTP 200 OK
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Allow: GET, POST, HEAD, OPTIONS
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Content-Type: application/json
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{
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"name": "To Do List",
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"description": "List existing 'To Do' items, or create a new item.",
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"renders": [
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"application/json",
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"text/html"
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],
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"parses": [
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"application/json",
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"application/x-www-form-urlencoded",
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"multipart/form-data"
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],
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"actions": {
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"POST": {
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"note": {
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"type": "string",
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"required": false,
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"read_only": false,
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"label": "title",
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"max_length": 100
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}
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}
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}
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}
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## Setting the metadata scheme
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You can set the metadata class globally using the `'DEFAULT_METADATA_CLASS'` settings key:
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REST_FRAMEWORK = {
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'DEFAULT_METADATA_CLASS': 'rest_framework.metadata.SimpleMetadata'
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}
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Or you can set the metadata class individually for a view:
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class APIRoot(APIView):
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metadata_class = APIRootMetadata
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def get(self, request, format=None):
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return Response({
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...
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})
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The REST framework package only includes a single metadata class implementation, named `SimpleMetadata`. If you want to use an alternative style you'll need to implement a custom metadata class.
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## Creating schema endpoints
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If you have specific requirements for creating schema endpoints that are accessed with regular `GET` requests, you might consider reusing the metadata API for doing so.
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For example, the following additional route could be used on a viewset to provide a linkable schema endpoint.
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@action(methods=['GET'], detail=False)
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def api_schema(self, request):
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meta = self.metadata_class()
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data = meta.determine_metadata(request, self)
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return Response(data)
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There are a couple of reasons that you might choose to take this approach, including that `OPTIONS` responses [are not cacheable][no-options].
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---
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# Custom metadata classes
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If you want to provide a custom metadata class you should override `BaseMetadata` and implement the `determine_metadata(self, request, view)` method.
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Useful things that you might want to do could include returning schema information, using a format such as [JSON schema][json-schema], or returning debug information to admin users.
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## Example
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The following class could be used to limit the information that is returned to `OPTIONS` requests.
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class MinimalMetadata(BaseMetadata):
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"""
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Don't include field and other information for `OPTIONS` requests.
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Just return the name and description.
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"""
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def determine_metadata(self, request, view):
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return {
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'name': view.get_view_name(),
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'description': view.get_view_description()
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}
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Then configure your settings to use this custom class:
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REST_FRAMEWORK = {
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'DEFAULT_METADATA_CLASS': 'myproject.apps.core.MinimalMetadata'
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}
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# Third party packages
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The following third party packages provide additional metadata implementations.
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## DRF-schema-adapter
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[drf-schema-adapter][drf-schema-adapter] is a set of tools that makes it easier to provide schema information to frontend frameworks and libraries. It provides a metadata mixin as well as 2 metadata classes and several adapters suitable to generate [json-schema][json-schema] as well as schema information readable by various libraries.
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You can also write your own adapter to work with your specific frontend.
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If you wish to do so, it also provides an exporter that can export those schema information to json files.
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[cite]: https://tools.ietf.org/html/rfc7231#section-4.3.7
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[no-options]: https://www.mnot.net/blog/2012/10/29/NO_OPTIONS
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[json-schema]: https://json-schema.org/
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[drf-schema-adapter]: https://github.com/drf-forms/drf-schema-adapter
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