I’m creating custom post type in a plugin for the first time. So far, it’s been done directly in the child theme. Not the best place as functionality should be separate from display.

The first thing was to copy, edit and paste one of the register_post_type() calls I had written before. Right away something was strange. The CPT showed up on my development site, but not on a blank install. After much commenting out of various lines, I found that the problem lay with the ‘capability_type’ argument.

My development site is multisite, and it looks like network admins have much more capabilities than normal site admins, or perhaps it was the role management plugin magically granting it rights. I looked into the code for the role management plugin (Members by Justin Tadlock) and discovered that it added some extra capabilities upon plugin activation. Sounds like just what I needed.

register_activation_hook( __FILE__, 'mbpc_feba_cpt_install' );

// Start by giving the administrator role access to the CPT
function prefix_cpt_install() {
	/* Get the administrator role. */
	$role =& get_role( 'administrator' );

	/* If the administrator role exists, add required capabilities for the plugin. */
	if ( !empty( $role ) ) {
		/* Role management capabilities. */
		$role->add_cap( 'publish_cptname' );
		$role->add_cap( 'create_cptname' );
		$role->add_cap( 'delete_cptname' );
		$role->add_cap( 'edit_cptname' );
	}

}

I’ve edited some of the names used. When you’re writing your own, remember to prefix your functions so they’ll be unique, and of course replace ‘cptname’ with a meaningful name.

Unfortunately, the code above did not work for me. It looked like the activation function was not being called. Putting echo statements inside didn’t do anything, and even putting die() inside did nothing.

When there’s a problem, start with the Codex. The page for register_activation_hook() had line near the bottom referencing a support forum thread. Turns out that ‘echo’ really doesn’t work, and the way to check if the activation hook is being called is to use exit().

Another user pointed out that __FILE__ doesn’t work when the plugin directory is only symlinked. That’s exactly what I’m doing! The solution is to pass it the path to the symlink.

register_activation_hook( WP_PLUGIN_DIR . '/plugin-name/plugin-name.php', 'prefix_cpt_install' );

And now the CPT shows up in the admin menus! wp_user_roles in the options table also has the new capabilities added by the activation function.