[wp-trac] [WordPress Trac] #30846: Custom query using tag__in sets query_var tag_id

[WordPress Trac]

#30846: Custom query using tag__in sets query_var tag_id
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 Reporter:  philbirnie         |       Owner:
     Type:  defect (bug)       |      Status:  new
 Priority:  normal             |   Milestone:  Awaiting Review
Component:  Taxonomy           |     Version:  4.1
 Severity:  normal             |  Resolution:
 Keywords:  reporter-feedback  |     Focuses:
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Changes (by boonebgorges):

 * keywords:   => reporter-feedback


Comment:

 philbirnie - Thanks for the detailed report.

 You're correct that `tag_id` gets set to the first member of `tag__in`.
 This happens primarily for backward compatibility, to ensure that the
 `tag_id` query var is always backfilled when viewing a taxonomy archive,
 in case themes attempt to reference it directly when (eg) setting up page
 titles. However, it's not referenced when building the SQL query itself.
 `WP_Query` converts all the query_vars passed directly to the class into a
 single unified `tax_query`; see
 https://core.trac.wordpress.org/browser/trunk/src/wp-
 includes/query.php#L1951. This tax query correctly recognizes the
 `tag__in` param. The `tag_id` backfilling happens afterward:
 https://core.trac.wordpress.org/browser/trunk/src/wp-
 includes/query.php#L2709

 The attached unit test [attachment:30846.test.diff] shows that this is
 working properly. Can you look at the logic there to make sure I'm
 understanding your report correctly?

 Double check to make sure you don't have any plugins or other
 customizations doing anything odd here. If you continue to have the
 problem even without any plugins, please share more detail about exactly
 *where* you're generating the query - the only possibility I can see is
 that there's something funny going on where you're trying to do a
 taxonomy-related query while on a single term's taxonomy archive page, or
 something like that.

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Ticket URL: <https://core.trac.wordpress.org/ticket/30846#comment:2>
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