tag_id Doesn't Work in WP_Query

[miqrogroove]

WP_Query::parse_query() stores a value in $qv['tag_id'] but it does not query the tag name, and WP_Query::get_posts() never checks the tag_id value. Thus, this variable does nothing.

I noticed this while working on #10640. The tag_id variable could be useful for the specific purpose of URL shortening where long tag slugs may be problematic (e.g. micro-blogging).

Leaving as "defect" because parse_query() is accepting a parameter that does not work.

Adding, however, that the lack of tag_id support in get_posts() appears to be by design and is not a bug in itself. Since the HTML class names of tags are like "tag-slug" rather than "tag-item-id", the ID numbers are currently a semi-private reference system. Website guests would have no use for ID queries, except within a plugin feature such as URL shortening.

Also note that any registered user can use edit-tags.php.

I ran accross this today..

Personally I think all references to it should probably just be removed, Unless it was implemented at some point in time.

I can see the usefulness of having access to the ID, but on MS sites that can change. The slug is a better source of reliable data. (Of course, the slug can be modified too tho).

On MS sites the tag ID can change? Is it different from the way post IDs and category IDs work?

Its not just Category ID's that change, Its Term ID's on all taxonomies. Whilst a single blog can always be assured to retain the same term ID, If another blog modifies the term, They recieve a new Term_id with their modifications, thats so they dont clobber one another's term details.

Its not like posts which are one after the other on a single blog, Terms can be shared accross blogs with MS.

Punting per IRC meetup. See also #12589.

I'm closing as a duplicate of #14166, as that has a patch.