I have been working with custom post types in WordPress for several years now, but never really found a suitable solution for ordering any of the default or custom columns properly. By default WP will order all custom post types by date, which sucks if you want them to sort by menu order, their title, or some other custom column you’ve created.
Every tutorial I came across (not to say every single one out there is wrong) either didn’t work for me, was outdated, etc. So, here’s how I just started doing it.
My custom post type is for floor plans for houses. They include bedrooms, bathrooms, dens, etc. The meta data is both text and numbers.
The first things I have done are add the pre_get_posts action with my custom function, then test to make sure that this is the admin screen and that the custom post type is being worked on.
After that, I found that $query->get( 'orderby' ); will always return a result, and I wanted to test for an empty value to be able to set my own. Once an orderby is set, it will be in the query array under the query object. With that somewhat explained, this is why I check to see if $query->query[ 'orderby' ] is empty or not, then set a variable accordingly.
The default sorting direction is desc, so I use the same method to test to see if it is set with $query->query[ 'order' ], defaulting it to asc if it is not set.
The big switch! Actually, this is all you really need to take a look at:
When sorting by a custom column, you must set a meta_key to sort by. You then set orderby to meta_value if it is a text sort and meta_value_num if it is a numerical sort. This can be seen with fp_pdf and fp_sf_tot respectively.
My default is menu_order due to I am using a plugin named Post Types Order to allow the users to drag and drop their order. If you do this, you will need to include the case for title as I have done. Or you could just make your default title.
I actually wouldn’t have gotten this far without Stephen Harris’ post Make Your Custom Column Sortable.