Can't seem to get set_blog_id working, it just doesn't reset the blog ID

Question

Trying to iterate through a list of the sites and I can't seem to get set_blog_id working. Here's the sample output:

Array ( [0] => stdClass Object ( [blog_id] => 2 ) [1] => stdClass Object ( [blog_id] => 3 ) [2] => stdClass Object ( [blog_id] => 5 ) )

get new_blog_id from array and check value - blog_id= 2

current_blog= 5

use set_blog_id to set current blog_id to new_blog_id

after set_blog_id, get_current_blog_id= 5 - should be 2

after resetting to oldblog get_current_blog_id 5

As you can see, everything is working but the set_blog_id. Here's the code. Any help would be appreciated!

function return_blog_first_posts(){
global $wpdb;

$site_blog_ids = $wpdb->get_results($wpdb->prepare("SELECT blog_id FROM wp_blogs where blog_id > 1")); /* get all subsite blog ids */
print_r($site_blog_ids); /*output check - "Array ( [0] => stdClass Object ( [blog_id] => 2 ) [1] => stdClass Object ( [blog_id] => 3 ) [2] => stdClass Object ( [blog_id] => 5 ) ) "
echo "</br>"; */

foreach( $site_blog_ids as $blog_id ) { /* iterate through the ids */
print_r( "</br>new blog_id check - blog_id= ".$blog_id->blog_id ); /* output check - this shows blog id */

echo "</br>current_blog= ".get_current_blog_id();
$newblogid = $blog_id->blog_id; //
$oldblog = $wpdb->set_blog_id( $newblogid ); // this is not working
echo "</br> after set_blog_id, get_current_blog_id= ".get_current_blog_id();
}
/* Tell the $wpdb object to go back to using the current site */
$wpdb->set_blog_id( $oldblog );
echo "</br> after resetting to oldblog get_current_blog_id ".get_current_blog_id();
}
return_blog_first_posts();

Answer 1

Use switch_to_blog( $new_blog_id ) instead.

You can find the function in wp-includes/ms-blogs.php.

Update

$wpdb->set_blog_id() doesn’t change the global variable $blog_id which is returned by get_current_blog_id(). switch_to_blog() does change the global variable.