While working on a large custom content management solution for a client I was building templates for multiple post types all sharing a common taxonomy. Most of these templates needed a dropdown to filter the results by the common taxonomy, in this case a taxonomy named “department.”
Should be fairly straight-forward, right? WordPress does offer a great function for creating taxonomy dropdowns called wp_dropdown_categories, which works with custom taxonomies as well as categories.
However, it will return all taxonomies with any posts. If you have multiple post types, you could very easily get a list of taxonomies with posts, but not the post type you want for the template – as was my issue.
Luckily, we can filter the SQL query used in the get_terms function, which is called by wp_dropdown_cateogies.
The above utilizes the term_clauses filter, and hunts for the post_type argument. The beauty of this is that we’re extending the functionality of the get_terms function directly.
This means we can use wp_dropdown_categories and simply pass our new post_type argument. Furthermore, the fallback here is the built-in function, which is a double bonus. I love the extend-ability of WordPress!
Here’s the basic usage, now that we have the filter above:
That said, I built a custom function to wrap the wp_dropdown_categories, so I could grab the current query var and add a wrapper element.
Here are some useful resources if you’re going down this rabbit hole:
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