Kentico: Custom Table `ItemKeyName` set to non-Primary key

ClonedCustomTableForm.ascx.cs

/* default */
form.ItemID = QueryHelper.GetInteger(ItemKeyName, 0);



/* by `ItemGUID` */
var ItemKeyNameID = QueryHelper.GetGuid(ItemKeyName, Guid.Empty);

/* option 1: get `ItemID` by custom table generated code */
/* saved code will be placed in /App_Code/CMSClasses */
form.ItemID = CMS.CustomTables.CustomTableItemProvider
              .GetItems<SubscribeToContentAlertItem>()
              .WhereEquals(ItemKeyName, ItemKeyNameID)
              .Column("ItemID")
              .FirstObject?.ItemID ?? 0;
              
/* option 2: get `ItemID` by custom table W/O generated code */ 
form.ItemID = CMS.CustomTables.CustomTableItemProvider
              .GetItems(customTable.ClassName)
              .WhereEquals(ItemKeyName, ItemKeyNameID)
              .Column("ItemID").FirstObject?.ItemID ?? 0;