easyui treegrid逐步加载

$("#bomStructureTable").treegrid({
    url : "systemcontroller?id=10007",//首次查询路径
    queryParams:{"bomid":"${bomid}"},//首次查询参数        
    columns : [ [{
        field : "name",
        title : "名称",
        width : 300
    } ] ],
    onBeforeExpand:function(row){
        //动态设置展开查询的url
        var url = "systemcontroller?id=10007&treeid="+row.treeid;
        $("#bomStructureTable").treegrid("options").url = url;
        return true;    
    }
});