Wordpress条件添加辅助角色

I need to create a function that works like this one of these:

Is primary user role Subscriber but NOT also any other secondary role? Then add the secondary role "Staff" to the user. So they are Subscriber & Staff.

I suck with conditional PHP. Can anyone give me a clean function?

There are a handful of User Role plugins out there that could help, such as Multiple Roles. I've personally not used it so I can't attest to how well it performs. If you just want a simple function, you will need to make use of the add_role() function on a WP_User object.

So, get your User Object however you want:

• If you want to do this to the currently logged in user, use wp_get_current_user().
• If you want to do this by user ID, you can use get_userdata().
• If you want to do this by another user field (username, email, etc. note: ID works here too) use get_user_by()

To run this for any user that's logged in, you can use something like this:

add_action( 'init', 'add_staff_role_to_subscriber');
function add_staff_role_to_subscriber(){
    if( is_user_logged_in() ){
        $user = wp_get_current_user();

        // If user is a Subscriber with NO other roles
        if( $user->roles[0] == 'subscriber' && ! isset( $user->roles[1] ) ){
            $user->add_role('staff');
        }
    }
}

What it does is make sure the current user is logged in, and then gets the WP_User object for that user. $user->roles is a single-dimensional array, so you can just make sure that the only role assigned to them is subscriber and that there is no second $role in the array by making sure $user->roles[1] isn't set, or is false.

Once the staff role is added to the user, the if statement will always be false since $user->roles[1] will be set to staff, or if they already have a secondary role it won't effect them.

Note, that in your question you have Subscriber capitalized, but roles are lowercase in WordPress, so I made staff lowercase in my code. You may need to make sure the capitalization matches before executing this code.