Is there a query string for edit.php to show all posts that have no custom taxonomy terms?

Question

I wrote a plugin Premium Posts that registers a custom taxonomy called sms_premium_posts and adds a column to the post list table in the WordPress administration area.

In that custom column, if a post has been marked Premium, the term Premium links to a filtered list of only premium posts. This link is generated using the query string:

http://www.example.com/wp-admin/edit.php?sms_premium_posts=premium

If a post is not marked as Premium, I would like the term Standard to filter the list so the table only shows posts that are NOT marked as premium (i.e. posts with no taxonomy terms).

Is there a query string for that?

Example query string:
http://www.example.com/wp-admin/edit.php?sms_premium_posts!=premium

You may ask, "Why not add the term Standard to all other posts?" My reason for not doing that is, it would require tagging all existing posts with a custom taxonomy term when the plugin is activated...which seems pretty inefficient.

Thanks in advance!

SOLUTION

Based on the answer from @s_ha_dum below, here is what I did to fake a negative query string:

function standard_term_filter( $query ) {
    if ( ! $query->is_admin || ! isset( $_GET['sms_premium_posts!'] ) )
        return $query;

    if ( 'premium' == $_GET['sms_premium_posts!'] ) {
        $taxquery = array(
            array(
                'taxonomy' => 'sms_premium_posts',
                'field'    => 'slug',
                'terms'    => 'premium',
                'operator' => 'NOT IN'
            )
        );
        $query->set( 'tax_query', $taxquery );
    }
    return $query;
}
add_action( 'pre_get_posts', array( $this, 'standard_term_filter' ) );

Note that I added this function as a method of my plugin class, which is why I used an array for the callback in add_action().

Also note the ! at the end of my query string term: sms_premium_posts!

I made my Standard term links look like this:

http://www.example.com/wp-admin/edit.php?sms_premium_posts!=premium

Since sms_premium_posts! is different than sms_premium_posts (the slug of my custom taxonomy), it works.

Answer 1

Use a tax_query with a NOT IN operator.

$args = array(
  'post_type' => 'post',
  'tax_query' => array(
    array(
      'taxonomy' => 'sms_premium_posts',
      'field' => 'slug',
      'terms' => 'Premium',
      'operator' => 'NOT IN'
    )
  )
);
$query = new WP_Query( $args );

Now, to make that work on the post edit page via a $_GET string something like what you have in your question, you could do this:

function alter_edit_php_query_wpse_100794($qry) {
  if(isset($_GET['notin'])) {
    $qry->set(
      'tax_query',
      array(
        array(
          'taxonomy' => 'category',
          'field' => 'slug',
          'terms' => sanitize_title_with_dashes($_GET['notin']),
          'operator' => 'NOT IN'
        )
      )
    );
  }
}
add_action('pre_get_posts','alter_edit_php_query_wpse_100794');

That is very rough. You probably want more conditionals, such as is_admin, to prevent that from working globally.

Reference

http://codex.wordpress.org/Class_Reference/WP_Query#Taxonomy_Parameters

Answer 2

It's not really possible without a tax query. You'd be better off assigning either the 'premium' or 'standard' term and never empty -- perhaps with a dropdown that holds a default value of 'Standard'.

If you'd rather not show 'Standard' over and over in the column you could always test for and hide it via the callback for manage_posts_custom_column.

See also: https://stackoverflow.com/questions/10582066/is-that-possible-to-use-in-query-string