How to get the main blog’s id and db prefix from a mu plugin?

4 comments

1. Use the constant BLOG_ID_CURRENT_SITE. And to get the database table prefix, use;

   $main_blog_prefix = $wpdb->get_blog_prefix(BLOG_ID_CURRENT_SITE);
   

   Log in to Reply

2. This is how we do it to be 100% as we have multiple main sites in the network installation:

   function name_ly_get_main_blog_id () {
     global $current_site;
     global $wpdb;
   
     return $wpdb->get_var ( $wpdb->prepare ( "SELECT `blog_id` FROM `$wpdb->blogs` WHERE `domain` = '%s' AND `path` = '%s' ORDER BY `blog_id` ASC LIMIT 1", $current_site->domain, $current_site->path ) );
   }
   

   Log in to Reply

3. You can use the below to get the table prefix.

   current site table prefix : $wpdb->prefix;
   Main blog table prefix : $wpdb->base_prefix;
   

   Log in to Reply

4. There’s a function to get main site id for a given network (defaults to the active network)

   get_main_site_id();
   

   If you only need db prefix, $wpdb->get_blog_prefix(get_main_site_id()) would suffice, but otherwise you can switch whole code blocks into other blog’s context seamlessly with switch_to_blog() and restore_current_blog() functions

   switch_to_blog(get_main_site_id());
   global $wpdb; // it's now in the main site's context
   $prefix = $wpdb->prefix;
   // ... do your stuff
   restore_current_blog();
   

   But be wary of recursive calls to switch_to_blog(), because then context becomes hard to track and debug

   Log in to Reply