WP_Term_Query not honoring orderby meta_value_num

[littler.chicken]

I think this is related to ticket #35381, the introduction of the WP_Term_Query class. I have a situation where I've created a taxonomy and pre-populated it with about 60 terms. The order is not alphabetical or anything, but should be consistent.

If I could be sure that no one would add new terms, I would order by ID and leave it at that, but new terms might be added in certain cases, so I've created a term metadata key and used a number for it to set the order. I've put a filter on get_terms_defaults to set the orderby to use the new term metadata.

In WP 4.5, this works--looks like 4.4 did not accept meta_value and meta_value_num for orderby yet. However, in trunk, the meta_value_num no longer works. As near as I can tell, the reason is that

$meta_clauses = $this->meta_query->get_clauses();

(line 817 of class-wp-term-query.php) is returning an empty value, so the $orderby parameter is returned as empty as well. I get completely bogged down when I try to diagnose any further in the WP_Meta_Query class, so I'm currently stumped. However, since it works in 4.5 and not in 4.6, I'm thinking it's a bug, so reporting it in the hopes that someone else can help sort this.

[boonebgorges]

Hi @littler.chicken - Thanks for the report.

I get completely bogged down when I try to diagnose any further in the WP_Meta_Query class

I was a bit bogged down too :) This is a pretty subtle issue. Briefly, the way that WP_Term_Query sanitizes the orderby parameter means that the meta query's SQL clauses must have been generated. This logic was changed in 4.6, which is why your previously-working code doesn't work anymore. It's possible to force the meta query to generate its SQL, but this uncovers a bug in WP_Meta_Query: running get_sql() doesn't reset the internal list of table aliases, which results in malformed SQL in some cases.

Could you test 37151.diff​ to see if it addresses your issue?

[littler.chicken]

Boone, thanks so much (and bonus points for making it look easy!). Tested your patch and it does correct the issue for me, in my scenario (sorting by term metadata/meta_value_num).

Thank you!

[boonebgorges]

@littler.chicken Thanks so much for verifying!

[boonebgorges]

In 37860:

Fix orderby meta handling for WP_Term_Query.

In order to allow meta-related values of orderby to be handled properly,
the term query's meta_query object must run its get_sql() method before
orderby parsing.

Fixing this bug required addressing another bug in WP_Meta_Query, which
caused the table alias index not to be reset when calling get_sql()
multiple times on the same object.

Props littler.chicken.
Fixes #37151.