CRM 2016 级联过滤 类比省市县

以下以省市为例:

    function preFilterLookup() {
    //要进行过滤的lookup按钮加入addPresearch事件    
Xrm.Page.getControl("shi").addPreSearch(function () {
            addLookupFilter();
        });
    }
    function addLookupFilter() {
        var sheng= Xrm.Page.getAttribute("sheng").getValue(); //客户类型
        if (sheng!= null) {
            fetchXml = "<filter type='and'><condition attribute='shi.sheng' operator='eq' value='" + sheng + "' /></filter>";
            Xrm.Page.getControl("shi").addCustomFilter(fetchXml);
        }
    }