Retrieve multiple records using javascript xrmservicetoolit in crm 2013 and crm 2015

function retrieve_multiple()
{

var stdId = Xrm.Page.data.entity.getId();
XrmServiceToolkit.Rest.RetrieveMultiple(
    "new_departmentSet",
    "?$select=new_Description&$filter=new_School/Id eq guid'"+stdId+"'",
    function (results) {
    var ab="";
    for (var i = 0; i < results.length; i++) {
         var Description = results[i].new_Description;
         //var new_School = results[i].new_School;
         //alert(Description);
          var des = Description == null ? 0 :  Description;
         ab=des+"-"+ab;
         if (ab!=null)
            {
            Xrm.Page.getAttribute("new_description").setValue(ab);
            Xrm.Page.getAttribute("new_description").setSubmitMode("always");
            }
            else
            {
            Xrm.Page.getAttribute("new_description").setValue("");
            Xrm.Page.getAttribute("new_description").setSubmitMode("always");   
            }
       
    }
    },
    function (error) {
         alert(error.message);
    },
    function () {
         //On Complete - Do Something
    },
    true
);
}