select value of an field in Lookup Selecting

How to selecting a value of an a field from same table in Lookup Selecting?$fld->Name == “idClienti” “select an field name” add a filter
eg: Ho to get the value of primarykey?
function Lookup_Selecting($fld, &$filter) {
if ($fld->idClienti->Value == 1 ?) {

}

This code:
if ($fld->idClienti->Value == 1 ?) {should be:
if ($this->idClienti->CurrentValue == “1”) {