Multiple Select Update Operation

hi to all,

i have just learned how to display saved multiple select values on update operation.

$tselected = explode(",",$model->columnname);

			foreach($tselected as $single)


				 $testsel[$single]   = array("selected"=>"selected");


from the above line columnname have id values like 1,2,3,4…

first i changed string to array. then each array i assign selected option.

echo $form->dropDownList(





				    	'key'=>'testid', 'class'=>'multiselect','options'=>$testsel)


finally create option parameter and pass array values