[wp-trac] [WordPress Trac] #56264: WP_Term_Query does not allow limiting results when descending family tree

[WordPress Trac]

#56264: WP_Term_Query does not allow limiting results when descending family tree
-----------------------------+-----------------------------
 Reporter:  get_dave         |      Owner:  (none)
     Type:  feature request  |     Status:  new
 Priority:  normal           |  Milestone:  Awaiting Review
Component:  Taxonomy         |    Version:  trunk
 Severity:  normal           |   Keywords:
  Focuses:                   |
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 == The Problem
 Over in https://github.com/WordPress/gutenberg/pull/42424 we're working on
 a way to limit the number of Category taxonomy terms that are displayed in
 the UI.

 This works well until you attempt to display top level terms only (i.e.
 those with a parent of 0). In this case the limit is **not applied**.

 Here is the Gutenberg PHP code where we apply the parent argument:

 https://github.com/WordPress/gutenberg/blob/10f8542e26e83262f177cdcca30ca57ae516e644/packages
 /block-library/src/categories/index.php#L27

 == Why does this happen?


 Digging into the Core code I noticed that `WP_Term_Query->get_terms()`
 method explicitly does not allow limiting when descending into the family
 tree of terms or when a parent is provided:

 https://github.com/WordPress/wordpress-develop/blob/6.0/src/wp-includes
 /class-wp-term-query.php#L628-L629

 The code comment states:

 > Don't limit the query results when we have to descend the family tree.

 There is no further information.

 Further investigation reveals that this "feature" was present in the
 original commit which introduced this functionality:

 https://github.com/WordPress/wordpress-
 develop/commit/8220d04e6d12c4a139344117e02fef268df5f205#diff-
 7813f38c6b905b75c4b11bf2750c63ba0f5a1227ffc4f012deeeb22999cee68bR1338-R1339


 == Feature Request

 I would like to display the top X categories but showing **top level terms
 only**. As it stands I don't believe this is possible.

 Perhaps we could introduce a clause in the conditional which allows
 limiting if the `$parent` is `0`?

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Ticket URL: <https://core.trac.wordpress.org/ticket/56264>
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