jQuery Grid Plugin - jqGrid

If I set a key:true for a column then the post data name is hard coded id not the name of the column.

Moreover if I want to set more than one column as key column then How can I do that?This is required if the table has more than one primary key.

The script is written below

<script src="./../js/min/grid.base-min.js" type="text/javascript"></script><script type="text/javascript">
 jQuery(document).ready(function(){
 jQuery("#unitgrid").jqGrid({
 url: './interfaceengine.xmlcreator?interface_id=griddemo&part_id=unitgrid',
 datatype: "xml",
colNames:[ ' ROLE ID ' ,'ROLE TITLE'], 
colModel:[
{name:'role_id',index:'role_id',width:105,key:false, hidden:true, editable:true,edittype:"text",editoptions: {size:30}},
{name:'title',index:'title',width:255,key:true, hidden:false, editable:true,edittype:"text",editoptions: {size:30}},],
 rowNum:6,
 rowList:[2,6,12,15],
 pager: jQuery('#pagered'),
 imgpath: './../themes/basic/images',
 sortname: 'id',
 viewrecords: true,
 sortorder:"desc",
 caption:"GRID",editurl:"./interfaceengine.DBGridEditServlet?interface_id=griddemo&part_id=unitgrid"
 }); 
 jQuery("#unitgrid").navGrid('#pagered',
 {}, //options
 {height:280,reloadAfterSubmit:false }, // edit options
 {height:280,reloadAfterSubmit:true}, // add options
 {reloadAfterSubmit:true}, // del options
 { } // search options
 );
});</script>