public void lookup(FormControl _formControl, str _filterStr)
{
    Query                   query = new Query();
    QueryBuildDataSource    queryBuildDataSource;
    SysTableLookup          sysTableLookup;

    sysTableLookup = SysTableLookup::newParameters(tableNum(ExcEC_DocuTypeTable), _formControl);
    queryBuildDataSource = query.addDataSource(tableNum(CustTable));

    sysTableLookup.addLookupField(fieldNum(CustTable, AccountNum));
    sysTableLookup.addLookupField(fieldNum(CustTable, Party));
    sysTableLookup.addLookupField(fieldNum(CustTable, RecId));

    sysTableLookup.parmQuery(query);
    sysTableLookup.performFormLookup();
}

public class BullFormBankAccountTable_Handler
{
public static BullFormBankAccountTable_Handler construct()
{
    return new BullFormBankAccountTable_Handler();
}

public void BankAccountTable_BullCust_OnLookup(FormDataObject _formDataObject, FormControl _formControl, str _filterStr)
{

    Query                   query = new Query();
    QueryBuildDataSource    queryBuildDataSource;
    SysTableLookup          sysTableLookup;

    sysTableLookup = SysTableLookup::newParameters(tableNum(BullDocuTypeTable), _formControl);
    queryBuildDataSource = query.addDataSource(tableNum(CustTable));

    sysTableLookup.addLookupField(fieldNum(CustTable, AccountNum));
    sysTableLookup.addLookupField(fieldNum(CustTable, Party));
    sysTableLookup.addLookupField(fieldNum(CustTable, RecId));

    sysTableLookup.parmQuery(query);
    sysTableLookup.performFormLookup();
}
}

[ExtensionOf(formStr(BankAccountTable))]
final public class BullFormBankAccountTable_Extension
{
[FormDataSourceEventHandler(formDataSourceStr(BankAccountTable, BankAccountTable), FormDataSourceEventType::Initialized)]
public static void BankAccountTable_OnInitialized(FormDataSource _sender, FormDataSourceEventArgs _e)
{
    var overrider = BullFormBankAccountTable_Handler::construct();

    _sender.object(fieldNum(BankAccountTable, BullCust)).registerOverrideMethod(methodStr(FormDataObject, lookup),
        methodStr(BullFormBankAccountTable_Handler, BankAccountTable_BullCust_OnLookup), overrider);
}

}