[wp-trac] [WordPress Trac] #41908: REST API gives wrong output when filtering posts with multiple category IDs - issue with AND operator

[WordPress Trac]

#41908: REST API gives wrong output when filtering posts with multiple category IDs
- issue with AND operator
------------------------------+-----------------------------
 Reporter:  subrataemfluence  |      Owner:
     Type:  defect (bug)      |     Status:  new
 Priority:  normal            |  Milestone:  Awaiting Review
Component:  REST API          |    Version:  4.8.1
 Severity:  normal            |   Keywords:
  Focuses:  rest-api          |
------------------------------+-----------------------------
 Encountered an issue while working with REST API which I am trying to
 explain below with test cases:

 Requirement:
 '''Filter out posts which are associated with category ids 2, 4 AND 3.'''

 REST API calls made:

 {{{
 http://example.com/wp-
 json/wp/v2/posts?filter[category__in][]=2&filter[category__in][]=3&filter[category__in][]=4
 }}}

 The above call fetched all available posts. Then I tried this:

 {{{
 http://example.com/wp-
 json/wp/v2/posts?categories=2&categories=4&categories=3
 }}}

 A better response this time, however, all posts having '''Category ID 3'''
 (the last one in the list) are returned even some of them don't have
 category ID 2 or 3 and some of have another category ID along with 3. In
 short this call gave me posts like this:

 '''Post A: 3, 9
 Post B: 3
 Post C: 3, 8, 12
 Post D: 2, 3, 6
 Post E: 2, 3, 4'''

 When I am expecting only '''Post E''' to come up.

 This time I changed the call a bit by putting the IDs in order:
 {{{
 http://example.com/wp-
 json/wp/v2/posts?categories=2&categories=3&categories=4
 }}}

 I got the correct result, i.e. only Post E came up this time.

 To extend my test a bit further I edited the post (Post E), removed
 Category ID 2 from it and then tried the same call again. '''This time I
 did not expect any result to come up because I am searching for posts
 associated with Category IDs 2, 3 AND 4'''. But I still get Post E even it
 is not associated with Category ID 2 anymore.

 Its a clean WP install, no plugin is there yet.

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Ticket URL: <https://core.trac.wordpress.org/ticket/41908>
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