2. Create a class and paste the copied event handler.
3. Write logic to perform action.
example:
/// <summary>
/// Runs the form <c>CaseDetail</c>.
/// </summary>
public static class CaseDetailExecQry
{
/// <summary>
/// <For case management>
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
[FormDataSourceEventHandler(formDataSourceStr(CaseDetail, CaseDetailBase), FormDataSourceEventType::QueryExecuting)]
public static void CaseDetailBase_OnQueryExecuting(FormDataSource sender, FormDataSourceEventArgs e)
{
CaseDetailBase caseDetailBase;
CaseCategoryHierarchyDetail detail;
select firstonly detail where detail.CategoryType == CaseCategoryType::Property;
while select * from caseDetailBase where caseDetailBase.CategoryRecId == detail.RecId
{
sender.query().dataSourceTable(tableNum(CaseDetailBase)).addRange(fieldnum(CaseDetailBase,CategoryRecId)).value(sysquery::value(detail.RecId));
}}}