foreach循环和一个来自sql的多个值的键

Question

I have problem to make one array with key ( class_id ) and in this key a lot of users_ids. I have function where $ids is an simple array with numbers. I'm trying to have sth like this:

array => 
   1 (class_id) =>
     0=> 'user_id'
     1=> 'user_id',
   2 (class_id) =>
     0=> 'user_id'
     1=> 'user_id'

Now I'm returning this ( only just with one user_id where there should be more:

array => 
   1=> 'user_id'
   2=> 'user_id'

static function getUsersIdsByClassIds($ids)
{
    $userIds = [];

    foreach($ids as $classId) {

        $object = self::select('user_id')
            ->where('class_id', $classId)
            ->get();

        foreach($object as $sth){
            $userIds[$classId]=$sth->user_id;
        }
    }

    return $userIds;
}

I cant fix it to do this structure I want.

Answer 1

in here

foreach($object as $sth){
   $userIds[$classId] = $sth->user_id;
}

you overwrite the value on each iteration. But you actually want to add a new entry:

foreach($object as $sth){
                // here it is
   $userIds[$classId][] = $sth->user_id;
}