Auto-remove custom field with no value on publish

2 comments

1. Demilio, unfortunately the WordPress API seems to assume that custom fields do not have an ’empty’ value, in the sense that update_post_meta and delete_post_meta, if given '' as the (previous) meta value perform the update/delete operation for all values for that key.

   This makes it difficult, for instance, if a custom field key has multiple values associated with it, some of which are empty and want to be removed.

   Below is the basic logic: It will only remove fields where all associated fields are ’empty’. Exactly what ‘empty‘ means, you can decide by specifying a callback to array_filter, by default, as used in the code below this includes ‘0’, false etc.

   The hook you are after is save_post. This is fired after the post and all it’s post-meta, has been saved having clicked ‘update’/’publish’, but also on auto-saves…

   add_action('save_post','my_cf_check');
   function my_cf_check($post_id) {
   
       // verify this is not an auto save routine. 
       if ( defined('DOING_AUTOSAVE') && DOING_AUTOSAVE ) return;
   
       //authentication checks
       if (!current_user_can('edit_post', $post_id)) return;
   
       //obtain custom field meta for this post
        $custom_fields = get_post_custom($post_id);
   
       if(!$custom_fields) return;
   
       foreach($custom_fields as $key=>$custom_field):
           //$custom_field is an array of values associated with $key - even if there is only one value. 
           //Filter to remove empty values.
           //Be warned this will remove anything that casts as false, e.g. 0 or false 
           //- if you don't want this, specify a callback.
           //See php documentation on array_filter
           $values = array_filter($custom_field);
   
           //After removing 'empty' fields, is array empty?
           if(empty($values)):
               delete_post_meta($post_id,$key); //Remove post's custom field
           endif;
       endforeach; 
       return;
   }
   

   As noted above, if a custom field key has multiple values associated with it, some of which are empty – they will not be removed. This will probably be ok for your use. There seems to be no easy ‘WordPress’ way around this. One way would be a custom MYSQL statement.

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2. Thanks Stephen Harris! You rock!

   Additionally, if you want to do this only for specific fields, you can put your specific values in an array, and compare it to the $custom_fields array with array_intersect().

   $result = !empty(array_intersect($specific_values, $custom_fields));
   

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