[solved]How to return data from database?

[eluser]tuckee[/eluser]
Hi guys, I am trying to convert the admin login username I got from the session into admin ID.

What I am trying to do here is I call the search_admin_id function in my model and return the id and store in $admin_id.

I got the error of "undefined variable : data" in my models/admin_model.php


My Controller

Code:

function approval()
{
  $this->load->model('Admin_model');
  $admin_username = $this->session->userdata('admin_username');

  $admin_id = $this->Admin_model->search_admin_id($admin_username);
  
}

My admin_model class

Code:

function search_admin_id($admin_username)
{
  
  $query_str = "SELECT admin_id FROM admin WHERE admin_username = ?";
  $query = $this->db->query($query_str, $admin_username);
  
  if($query -> num_rows() > 0 )
  {
   return $data;
  }

}

Can anyone help me? Any help is much appreciated.