get_user_meta() to Return User Meta Only for Current Blog in Multi Site

Question

I've written a plugin that allows users to bookmark their favorite posts, but have run into a small problem when using it on a multisite network.

Each time a post is bookmarked, the ID of that post is stored in an array of IDs in the current user's meta table. This all works great, until it's used on a MS setup.

If viewing the site that the bookmarks were created on, everything works great, but when viewing a different site, I get a list of post IDs that belong to the other site. This is because the user meta table is shared between sites.

So, what I need to do is retrieve only the user meta for the current site. Is there a way to do this? I don't think there is, so if anyone has some insight, that'd be great.

Answer 1

WordPress distinguishes usermeta keys between sites by using the database prefix for each site.

For example, instead of using the favorite_posts key, you'd use the meta key wp_23_favorite_posts. To get the prefix, you can use $wpdb->get_blog_prefix().

But wait, there's actually a whole API dedicated to this. Rather than using *_user_meta(), use *_user_option(). These are internally translated to be against the individual site.

And, it's easily integrated into your existing plugin. get_user_option() checks against a site-specific key first, but if it doesn't find anything, it falls back to a user-wide meta key. So go ahead and switch to get_user_option() and your existing plugin will work on single site without a problem.

Here are the function definitions:

./wp-includes/user.php:251:function get_user_option( $option, $user = 0 )
./wp-includes/user.php:293:function update_user_option( $user_id, $option_name, $new_value )
./wp-includes/user.php:322:function delete_user_option( $user_id, $option_name )

Answer 2

why not store the blog id together with the array of postIds, so you will have something like this stored in the user meta data:

Array
(
   [blogid1] => Array(1,2,4,7),
   [blogid2] => Array(3,6,8,10)
)

you can use the global $blog_id to get the current blogid. On a non multisite setup, the blogid will be 0 and should still work when you try to get the posts out the array by

arr[$blog_id]