Custom field for CMB2.
The post IDs are saved in an array, which can be rearranged by dragging and dropping posts in the attached posts column.
If the ability to search for a post and attach it is more in line with what you need, you might consider CMB2 Post Search field instead.
Follow the example in example-field-setup.php for a demonstration. The example assumes you have both CMB2 and this extension in your mu-plugins directory. If you're using CMB2 installed as a plugin, remove line 6 of the example.
In the example file example-field-setup.php, the field is added using the prefix _attached_cmb2_ and the name attached_posts which results in a meta key of _attached_cmb2_attached_posts. The example also demonstrates how to modify the get_posts query args.
You can retrieve the meta data using the following:
$attached = get_post_meta( get_the_ID(), '_attached_cmb2_attached_posts', true );This will return an array of attached post IDs. You can loop through those post IDs like the following example:
foreach ( $attached as $attached_post ) {
$post = get_post( $attached_post );
}Once you have the post data for the post ID, you can proceed with the desired functionality relating to each attached post.