Allow WP_Comment_Query::query to filter by category

[sambauers]

The attached patch allows WP_Comment_Query::query to accept three additional arguments:

• cat
• category__in
• category__not_in

The resulting comments are then filtered by these category arguments as well as any other arguments.

These arguments work the same way as their WP_Query counterparts.

I would appreciate advice on the appropriateness of using INNER JOIN (as I have done here) to join in the taxonomy tables to the query.

[sambauers]

The argument list got a bit munged there. The last two arguments should have double underscores after "category". Here is the relevant link in the codex to how WP_Query works with these arguments:

​http://codex.wordpress.org/Class_Reference/WP_Query#Category_Parameters

That is the argument usage I have followed for this patch.

[boonebgorges]

Thanks for the patch, sambauers.

Adding these table joins into WP_Comment_Query is pretty unappealing. In WP_Query, all (or at least most) of the category query logic has been moved to WP_Tax_Query. So, if we were going to add something like this, we'd want to do it with WP_Tax_Query instead of by building the SQL like this. I guess the relevant argument for WP_Comment_Query would then be something like 'post_tax_query', since we would want to leave the door open for putting taxonomy on comments at some point in the future.