I’d make 2 queries. This would look something like this :
function add_role_filter_to_posts_administration(){
//execute only on the 'post' content type
global $post_type;
if($post_type == 'post'){
$user_role="";
// Get all user roles
$user_roles = array();
foreach ( get_editable_roles() as $key => $values ) :
$user_roles[ $key ] = $values['name'];
endforeach;
// Set a selected user role
if ( ! empty( $_GET['user_role'] ) ) {
$user_role = sanitize_text_field( $_GET['user_role'] );
}
?><select name="user_role">
<option value=""><?php _e( 'All Roles', 'papasemarone' ); ?></option><?php
foreach ( $user_roles as $key => $value ) :
?><option <?php selected( $user_role, $key ); ?> value="<?php echo $key; ?>"><?php echo $value; ?></option><?php
endforeach;
?></select><?php
}
}
add_action('restrict_manage_posts','add_role_filter_to_posts_administration');
function add_role_filter_to_posts_query( $query ) {
/**
* No use on front
* pre get posts runs everywhere
* even if you test $pagenow after, bail as soon as possible
*/
if ( ! is_admin() ) {
return;
}
global $pagenow;
/**
* use $query parameter instead of global $post_type
*/
if ( 'edit.php' === $pagenow && 'post' === $query->query['post_type'] ) {
if ( isset( $_GET['user_role'] ) ) {
$role = $_GET['user_role']; // return string 'contributor_facebook'
$users = new WP_User_Query( array( 'role' => $role ) );
$results = $users->get_results();
$user_ids = array();
foreach( $results as $result ) {
$user_ids[] = (int) $result->ID;
}
/**
* I use PHP_INT_MAX here cause 0 would not work
* this means "user that does not exist"
* this trick will make WP_Query return 0 posts
*/
$user_ids = ! empty( $user_ids ) ? $user_ids : PHP_INT_MAX;
$query->set( 'author__in', $user_ids );
}
}
}
add_action( 'pre_get_posts', 'add_role_filter_to_posts_query' );
You need to make a User query to get all users that have specific role and then query posts with the “author” parameter.