how to set a 2nd level subject tree to force select

Senario is:

when selected: check if the <subject> has <parentsubject> if not then
msg: "please select a child subject tree" set focus back to subject
else
leave as <parent subject>




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function GetAttributeValueFromID(sEntityName, sGUID, sAttributeName, sID)

{
var xml = "" +
"<?xml version=\"1.0\" encoding=\"utf-8\"?>" +
"<soap:Envelope xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\">" +
GenerateAuthenticationHeader() +
" <soap:Body>" +
" <RetrieveMultiple xmlns=\"http://schemas.microsoft.com/crm/2007/WebServices\">" +
" <query xmlns:q1=\"http://schemas.microsoft.com/crm/2006/Query\" xsi:type=\"q1:QueryExpression\">" +
" <q1:EntityName>"+sEntityName+"</q1:EntityName>" +
" <q1:ColumnSet xsi:type=\"q1:ColumnSet\">" +
" <q1:Attributes>" +
" <q1:Attribute>"+sAttributeName+"</q1:Attribute>" +
" </q1:Attributes>" +
" </q1:ColumnSet>" +
" <q1:Distinct>false</q1:Distinct>" +
" <q1:PageInfo>" +
" <q1:PageNumber>1</q1:PageNumber>" +
" <q1:Count>1</q1:Count>" +
" </q1:PageInfo>" +
" <q1:Criteria>" +
" <q1:FilterOperator>And</q1:FilterOperator>" +
" <q1:Conditions>" +
" <q1:Condition>" +
" <q1:AttributeName>"+sID+"</q1:AttributeName>" +
" <q1:Operator>Equal</q1:Operator>" +
" <q1:Values>" +
" <q1:Value xsi:type=\"xsd:string\">"+sGUID+"</q1:Value>" +
" </q1:Values>" +
" </q1:Condition>" +
" </q1:Conditions>" +
" </q1:Criteria>" +
" </query>" +
" </RetrieveMultiple>" +
" </soap:Body>" +
"</soap:Envelope>" +
"";

var xmlHttpRequest = new ActiveXObject("Msxml2.XMLHTTP");
xmlHttpRequest.Open("POST", "/mscrmservices/2007/CrmService.asmx", false);
xmlHttpRequest.setRequestHeader("SOAPAction","http://schemas.microsoft.com/crm/2007/WebServices/RetrieveMultiple");
xmlHttpRequest.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
xmlHttpRequest.setRequestHeader("Content-Length", xml.length);
xmlHttpRequest.send(xml);
// retrieve response and find attribute value
var result = xmlHttpRequest.responseXML.selectSingleNode("//q1:" + sAttributeName);
if (result == null)
return "";
else
return result.text;
}
id=crmForm.all.subjectid.DataValue[0].id;
name=GetAttributeValueFromID("subject",id, "parentsubject", "subjectid");
if(name>"0")
alert("it has parent");
else
{
alert("it has not parent");
crmForm.all.subjectid.DataValue=null;
}