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I have a simple dependency check at the start of some plugins - which check if another plugin is installed and active (using class_exists()).

This works well in the normal WordPress flow - as the plugin that includes the required class is set to instantiate earlier and I also re-order the available plugins so this plugin is loaded first - like this:

     * Force this plugin to load first
     * @since   0.1
     * @return  void
    public function load_this_plugin_first() 

        // grab plugin directory + file name ##
        $path = plugin_basename(dirname(__FILE__)).'/'.basename(__FILE__);

        // grab the list of active plugins ##
        if ( $plugins = get_option( 'active_plugins' ) ) {

            // check if out plugin is in there ##
            if ( $key = array_search( $path, $plugins ) ) {

                // push it to the top of the list ##
                array_splice( $plugins, $key, 1 );
                array_unshift( $plugins, $path );
                update_option( 'active_plugins', $plugins );




This all works well until I need to update a plugin - then the other plugins are all deactivated - as all the class_exists() checks return false.

So, I'd like to know if there is a constant - such as DOING_AUTOSAVE for plugin updates - something like DOING_PLUGIN_UPDATE?

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up vote 3 down vote accepted

Instead of re-ordering your plugins to load in a specific order, have each of them that requires some other plugin to be loaded to defer their initialization until the "plugins_loaded" action hook.

In other words, when a plugin with a dependency is included and ran, it shouldn't do anything directly. Instead, it should have functions, and then add_action calls to hook those functions to plugins_loaded. That function that is called later can do the class_exists check and act accordingly.

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thanks for the suggestion, I'm going to need to re-write a few things then I'll come back with feedback! – Q Studio Jan 10 '14 at 8:36
little juggling - changed a few methods to static and got this all working nicely - thanks! – Q Studio Jan 15 '14 at 17:37

How about using WP_INSTALLING? - this check is placed above the main plugin Class...

if ( ! class_exists( 'REQUIRED_CLASS_NAME' ) && ! defined( 'WP_INSTALLING' ) )  { 

    // give some notice to the user ##
    add_action('admin_notices', function(){
        $plugin = get_plugin_data( __FILE__ );
        echo "<div id='message' class='error'><p><code>".$plugin["Name"]."</code> has been deactivated because it requires the <a href='#'>PLUGIN NAME</a>.</p></div>";
        if ( isset( $_GET['activate'] ) ) {
            unset( $_GET['activate'] ); // remove the activation notice ##

   // turn this plugin off ##
   add_action('admin_notices', function(){
      deactivate_plugins( plugin_basename( __FILE__ ) );

   // stop this plugin from running ##

Then the actual plugin class is below:

if ( ! class_eixsts( "Plugin_Class" ) ) 
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