[wp-trac] [WordPress Trac] #50244: Add bulk operation support to the Rest API

[WordPress Trac]

#50244: Add bulk operation support to the Rest API
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 Reporter:  andraganescu              |       Owner:  TimothyBlynJacobs
     Type:  feature request           |      Status:  assigned
 Priority:  high                      |   Milestone:  5.5
Component:  REST API                  |     Version:  4.4
 Severity:  normal                    |  Resolution:
 Keywords:  has-patch has-unit-tests  |     Focuses:  performance
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Comment (by TimothyBlynJacobs):

 I've created a PR with a first pass at what this could look like. Things
 for thoughts:

 1. I don't really love this being in `wp/v2`, it isn't really part of the
 `wp` data namespace. I kinda would like it do just be `wp-json/batch`.
 2. Should routes have to opt-in to supporting batching? We could have a
 `register_rest_route` flag like `allows_batch`. While theoretically any
 properly coded route wouldn't have an issue being used in this manner, not
 every route is properly coded ( #50239 ).
 3. We could also support a `validate_callback` in the
 `register_rest_route` on the same level as `callback` and
 `permission_callback` that would take a `WP_REST_Request` object and do
 validation for it. This would be helpful for cases where validation has to
 be done with all the fields together as context, not just individual field
 validation. We'd do the parameter validation first, and then call
 `validate_callback` on the whole request.
 4. I'm thinking about registering the batch controller as part of
 `WP_REST_Server` itself like the namespace routes. That way we don't have
 to expose the `match_request_to_handler` method.
 5. In `pre` validation mode, validation will happen twice. Once when we
 check every request for passing validation, and then again in the
 individual dispatch. Adjusting this to only happen once makes me nervous,
 but there would be a performance benefit to it only happening once.
 6. The `maxItems` number is fairly arbitrary, and isn't currently
 implemented #48821.
 7. I've omitted support for `GET` requests entirely at the moment. The
 other requests will have their own permission checks, so it is more
 difficult for an unscrupulous person to create a lot of load. But if we
 allow `GET` requests this could easily get out of control with no
 permission checks, and the permission checks are non-obvious. I think we
 should also encourage using linking/embedding over a batch `GET` for the
 time being. So I'd like to punt `GET` batching to a later release.

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Ticket URL: <https://core.trac.wordpress.org/ticket/50244#comment:7>
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