users.md

User Meta

This section of research covers adding and editing usermeta fields to the various wp-admin forms.

Registering Custom Usermeta Fields

"Registering" new usermeta fields must be accomplished by echoing HTML via different actions depending on the context.

In some contexts, you must echo a single table row, while in others you will need to echo an entire table, perhaps including a header as well.

Note: It is important to include the wp-admin css classes so the new fields blend in with the admin.

See

• Add User
• Profile / Edit User

Saving Custom Usermeta Fields

All user forms include 'user.php' and use the edit_form() function to perform user insert and updates. Yes, adding users also uses the edit_user() function.

Filter: insert_custom_user_meta

The insert_custom_user_meta filter appends an arbitrary array immediately prior to running update_user_meta() with each element in the array inside wp_insert_user() (see wp-includes/user.php).

To attach a new meta we inform wp_insert_user() about the previously unassigned $_POST value.

add_filter( 'insert_custom_user_meta', 'attach_new_meta_field' );

public function attach_new_meta_field() {
	if ( ! isset( $POST['new_meta_key'] ) ) {
		return [];
	}
	
	return array( 'new_meta_key' => sanitize_text_field( $_POST['new_meta_key'] ) ); 
}