Here's the function I have in my theme's functions.php:

function better_editions( $query ) {

    // Categories act as 'Editions' on my site

    $get_edition = get_query_var( 'category_name' );
    if( $get_edition !== '' ) {
        $edition = get_term_by( 'slug', $get_edition, 'category' );
        if( $edition && !is_wp_error( $edition ) ) {
            $edition = $get_edition;

    if ( $query->is_category() && isset($edition) && $query->is_main_query() ) {
        $query->set( 'post_type', array( 'post' ) );
        $query->set( 'category_name', $edition.', intl' );
add_action( 'pre_get_posts', 'better_editions' );

I use the function to display posts that belong to 'International (intl)' category under all categories (in all category archives, category posts listings, etc).

As I learnt, in order to define multiple categories with category_name in $query->set();, this is the only way, unless I am wrong:

$query->set( 'category_name', 'category1, category2' );

Which is what I am doing, as shown in the function far above.

The problem is, with the function in place, I get this error:

Notice: Array to string conversion in /var/www/wp.dev/public/wp-admin/edit.php on line 225

The error is only visible with debug turned on, and only on category-specific "All Posts" page. For example...


...the above link lists all posts under "International (intl)" category in wp-admin.

What am I doing wrong in the function? How do I fix this?

NOTE: I don't want to use !is_admin() because I want the function to apply to wp-admin as well.


I am unable to duplicate the problem, but the Notice references this line:

add_screen_option( 'per_page', array( 'label' => $title, 'default' => 20, 'option' => 'edit_' . $post_type . '_per_page' ) );

And that makes me think that you should be passing a post type in your GET string.


Just a guess as I can't duplicate the issue. If that doesn't move you forward I will delete the answer :)

  • Whoa! That tip did it! It's that I am setting the post type on this line: $query->set( 'post_type', array( 'post' ) );. Removing it from the function resolved the problem, while retaining all functionality. Thank you very much! If possible, please edit your answer to make note of this. – its_me Nov 23 '13 at 18:30
  • On my phone, I'll update later. Glad it helped. – s_ha_dum Nov 23 '13 at 18:42

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