如何从下拉列表中显示所选值

Question

I have a table with 3 columns. The first is name of the student. The second column is a dropdown, in which it should be selected the teacher that teaches this student from first column and the other values in this dropdown should be other teachers and it could change teacher.And third column is submit button - to save changes (if you have changed the teacher for this student). I use "selected=selected", but it selects in all rows only one teacher, not dependent on what is in db.Here's my view:

foreach ($students_show as $row)
{

?>
<tr>
<td>
    <?php echo $row->username; 
</td>
<?php
echo "<select name = 'add_teacher[]' >";
    foreach($teachers_show as $row) 
    {

        ?>
        <option value= '$row->username '
        <?php echo $row->username == $row->username  ? 'selected="selected"' : '' ?>><?php echo $row->username ; ?></option>


    <?php 
  } 
    echo "</select>";
    ?>
    </td>

My model is:

public function stdents_show()
    {
        $this->db->select('*');
        $this->db->from('users');
        $this->db->where('role_id', '2');
        $result=$this->db->get();
            return $result->result();
    }
       public function teacher_show()
    {

        $this->db->select('teacher_id, users.username');
        $this->db->from('teacher_conn');
        $this->db->distinct('teacher_id');
        $this->db->join('users', 'users.user_id=teacher_conn.teacher_id');

        $result=$this->db->get();
            return $result->result();
    }

Answer 1

You used $row for both student and teacher. use this way :

foreach ($students_show as $student)

and

foreach($teachers_show as $teacher) 

and compare should be like this

<?php echo $teacher->username == $student->teahcer_name? 'selected="selected"' : '' ?>><?php echo $teacher->username ; ?></option>