Ext.data.JsonReader 解析联合主键 求教？

json数据格式 联合主键： id":{"code":"99","type":"99"}

{"list":[
{"contractPeople":"99","description":"99","id":{"code":"99","type":"99"},"infoSource":"1","infoSourceType":"1","note":"99","usebyDepartment":"99"},
{"contractPeople":"98","description":"98","id":{"code":"98","type":"98"},"infoSource":"1","infoSourceType":"1","note":"98","usebyDepartment":"98"},
{"contractPeople":"97","description":"97","id":{"code":"97","type":"97"},"infoSource":"1","infoSourceType":"1","note":"97","usebyDepartment":"97"},

              reader:new Ext.data.JsonReader(
              {   
                    idProperty: 'id',
                    root: 'list',
                    totalProperty: 'totalCount',
                    fields: [
                        {name:'id',mapping:'type'},
                        { 'id': 1, 'name': 'type', mapping:'type' },
                        { 'id': 2, 'name': 'code', mapping:'code'},
                        {name:'description'},
                        {name:'usebyDepartment'},
                        {name:'contractPeople'},
                        {name:'infoSourceType'},
                        {name:'infoSource'},
                        {name:'note'}
                    ]



                }
             )

这么写解析不了联合主键的json数据 求教有经验的 多谢

http://www.extjs.com/deploy/dev/examples/grid/xml-grid.js

http://www.extjs.com/deploy/dev/examples/grid/xml-grid.html