I need to add a category to about 2500 posts, and either need to use an SQL query or wp_set_object_terms with PHP. I'm looking at wp_set_object_terms so I can add a category and not impact the currently assigned categories.

The function below that uses wp_set_object_terms' (from the WordPress Codex) adds one or more categories from an array (in the case of the example, categories 6 and 8) to the post with the ID of 42 (in the example).

But I need to be able to add an array of post IDs ($object_id), not an array of categories.

According to https://codex.wordpress.org/Function_Reference/wp_set_object_terms, $object_id has to be a single integer.

How can I use an array of ~2500 post IDs for $object_id? Do I need to a for each loop and run through the array and process each category addition to each post ID one at a time?

From https://codex.wordpress.org/Function_Reference/wp_set_object_terms :

// An array of IDs of categories we to add to this post. (Not using an array)
$cat_ids = array( 6, 8 );

// Add these categories, note the last argument is true.
// (42 is the $object_id; I will hardcode the category ID)
$term_taxonomy_ids = wp_set_object_terms( 42, $cat_ids, 'category', true );

if ( is_wp_error( $term_taxonomy_ids ) ) {
    // There was an error somewhere and the terms couldn't be set.
} else {
    // Success! These categories were added to the post.

1 Answer 1


I doubt it would justify the effort of writing custom SQL queries for only 2500 posts.

Within the wp_set_object_terms( $object_id, ... ) function we have:

$object_id = (int) $object_id;

so it's correct that it only takes a single post id as input.

So you would need to loop over your $post_ids array but it might be sufficient to use the wp_defer_term_counting() trick1):

 * Add terms to posts (with debug display)
function wpse_terms_to_posts( $terms, $taxonomy, $append, &$post_ids )
    wp_defer_term_counting( true );

    print '<ul>';
    foreach( (array) $post_ids as $post_id )
        $tt_ids = wp_set_object_terms( $post_id, $terms, $taxonomy, $append );

        print '<li>';
        if( is_wp_error( $tt_ids ) )
                'Problem adding terms to post_id: %d - Error: %s',
            print 'Success adding terms to post_id: ' . $post_id ;
        print '</li>';
    print '</ul>';

    wp_defer_term_counting( false );

Here we pass $post_ids by reference in case it's very large.

Usage (PHP 5.4+) :

    $terms     = [ 6, 8 ],
    $taxonomy  = 'category',
    $append    = true,
    $post_ids  = [ 123, 234, 345 ]

We could even slice the $post_ids array, if 2500 is too much for our system in a single run.

Here's an example how we can run the function with admin-ajax.php with such a slicing feature:

We create our own action with:

 * Custom wp ajax action to activate our wpse_terms_to_posts() function
 * Example: /wp-admin/admin-ajax.php
 *          ?action=wpse-terms-to-posts&wpse_offset=0&wpse_length=500
add_action( 'wp_ajax_wpse-terms-to-posts', function()
    $offset = filter_input( INPUT_GET, 'wpse_offset', FILTER_SANITIZE_NUMBER_INT );
    $length = filter_input( INPUT_GET, 'wpse_length', FILTER_SANITIZE_NUMBER_INT );

    // Check for user capability and non empty user input:
    if( current_user_can( 'manage_options' ) && '' !== $offset && '' !== $length  )
        print '<h3>Start:</h3>';      
        $start = microtime( true );

        // Settings - Edit to your needs:
        $terms     = [ 6, 8 ];
        $taxonomy  = 'category';
        $append    = true;
        $post_ids  = [ 123, 234, 345, 456, 567, 678, 789 ];

        // Add terms to posts:
        wpse_terms_to_posts (
            array_slice( $post_ids, $offset, $length )

        printf( '<h3>Done in %f seconds</h3>', microtime( true ) - $start );         

} );

where we use the wpse_offset and wpse_length GET parameters to slice the posts array.

If we want to slice the post ids array into chunks of 500, we can activate it manually with:






That way we can check for any term errors.

Hope you can modify this to your needs.

1) wp_defer_term_counting() was first mentioned on WPSE in this answer by @JanFabry

  • Thanks for the effort! Looks to be exactly what I need. Sorry, just learning here: where does the "usage" wpse_terms_to_posts ( $terms... go? Inside the function? I get a parse error on it. Jun 22, 2015 at 3:30
  • I assume PHP 5.4+ by using the [] array notation, that could be the parse error you got? I updated the answer with an example how you can activate the wpse_terms_to_posts function via admin-ajax.php. @markratledge
    – birgire
    Jun 22, 2015 at 10:01
  • I love this approach. I had a foreach loop in mind, but with the huge amount of posts, the actual operation can bom out due to memory or time. :-). Your approach caters well for this issues Jun 22, 2015 at 10:03
  • It's handy if we want to watch out for errors (then I usually don't print out the successful inserts ). One could also log the errors into a file instead. If the number of manual "slice" calls is too large, then I sometimes use a linux cron script with curl or wget. Then we need a no_priv type of action. We could also check out the upgrade process from the multisite with auto refresh from javascript, where the browser page must be open during the process. @PieterGoosen
    – birgire
    Jun 22, 2015 at 10:10
  • Very nice; let me check this out later today. Jun 22, 2015 at 19:29

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