Create a class extension of the table you want to add display method to and then add the display method
[ExtensionOf(tableStr(CustTable))]
final class CustTable_Extension
{
public static class CustTable_Extension
{
[SysClientCacheDataMethodAttribute(true)]
public static display Name custGroupName(CustTable _this)
{
return CustGroup::find(_this.CustGroup).Name;
}
}
}