Ext下拉列表不能显示问题

js里面的代码如下：var department = Ext.data.Record.create([
    {name: 'signature'},
    {name: 'departmentName'}
]);
var dataStoreModel=new Ext.data.Store({      
    proxy: new Ext.data.HttpProxy({url: 'sampleDictionary!getOrganize.exec',disableCaching:true,failure : function() { 
        Ext.Msg.alert("字典一级分类加载失败,请检查!");
    }}),
    reader: new Ext.data.JsonReader({    
       totalProperty: "results", 
       root: "rows",
       id: "id" 
    },department),      
    remoteSort: true
});//下拉框
                     {
                        id:    'department',
                        displayField:'departmentName',
                        valueField:'signature',
                        hiddenName: 'signature',
                        fieldLabel:     '所属部门',
                        xtype:'combo',
                        overflowX:false,
                        store:dataStoreModel,
                        //store:departmentArr,//数据源为一数组
                        typeAhead: true,
                        mode: 'local',
                        triggerAction: 'all',
                        selectOnFocus: true,
                        editable: false,
                        emptyText:'请选择....',
                        allowBlank: false,
                        blankText : '请选择!',
                        anchor:            '94%',
                     }
getOrganize()方法如下： StringBuilder json = new StringBuilder();
   List<OssSysOrganize> list = null;
OssSysOrganize organize = null;
for (int i = 0; i < organizeList.size(); i++) {
organize = organizeList.get(i);
list = hibernateTemplateDAO.createCriteria(OssSysOrganize.class, Restrictions.and(Restrictions.eq("pid", organize.getCid()),Restrictions.isNotNull("signature"))).list();
json.append("{totalCount: "+list.size()+",rows: [");
for(OssSysOrganize org : list){
json.append("{'signature':'"+org.getSignature()+"','departmentName':'"+org.getName()+"'},");
}
}
if(json.length() > 0)
json.deleteCharAt(json.length()-1);
json.append("]");在我点击编辑时已经进行了加载：
dataStoreModel.load();
如此，点击时没有下拉列表,请高手指教！补充：值可以传回来，在FireBug里面传回来的值如下：
{totalCount: 4,rows: [{'signature':'COMPONENT_PRE_DEPART','departmentName':'元件检测专业组'},{'signature':'DEVICE_PRE_DEPART','departmentName':'器件检测专业组'},{'signature':'FAILURE_ANALYSIS_DEPART','departmentName':'失效分析专业组'},{'signature':'SCREENING_TEST_DEPART','departmentName':'筛选试验专业组'}]求解谢谢