combining set_relation and callback_field

hello, i have this condition,

My Tables are:

+----------------------------+
|       tbl_training         |
+----------------------------+
|kd_training | nama_training |
+------------+---------------+
|   0001     | 1st  training |
|   0002     | 2nd  training |
|   0003     | 3rd  training |
+------------+---------------+

+-----------------------------------+
|         tbl_batch_training        |
+-----------------------------------+
| kd_batch | kd_training | no_batch |
+----------+-------------+----------+
|     A    |     0001    |     1    |
|     B    |     0001    |     2    |
|     C    |     0002    |     1    |
|     D    |     0002    |     2    |
+----------+-------------+----------+

+--------------------------+
|       tbl_assignment     |
+--------------------------+
| kd_assignment | kd_batch |
+---------------+----------+
|      A1       |    A     |
|      A2       |    C     |
|      A3       |    D     |
+---------------+----------+

on my controller:

$crud->set_table('tbl_assignment');
$crud->set_subject('Assignment');
if($state != 'edit')
{
	$crud->callback_column('kd_batch',array($this,'_column_callback_kd_batch'));
} else {
	$crud->set_relation('kd_batch','tbl_batch_training','{kd_training} - {no_batch}');
}

_column_callback_kd_batch:

function _column_callback_kd_batch($value, $row)
{
	//it turns 'D' into '2nd training, Batch number 2'
}

as we see there, when browsing the flexigrid, we will see the kd_batch shown '{nama_training}, batch number {no_batch}'

but, on edit/insert, it will shown 0001 - 1

instead, i want to make kd_batch on tbl_assignment listing shown:

1st training, Batch number 1
2nd training, Batch number 1
2nd training, Batch number 2

as a flexigrid's dropdown menu (with search box)

how to do that?

combining set_relation and callback_field

HenryJahja