look up for item id

public void lookup()
{
    Query query = new Query();
    QueryBuildDataSource qbds,qbds1;
    SysTableLookup sysTableLookup;
    QueryBuildRange qbr;
   Parameter      parameter;
    //super();
    sysTableLookup = SysTableLookup::newParameters(tablenum(InventTable), this);

    qbds = query.addDataSource(tableNum(InventTable));
    qbds1 = qbds.addDataSource(tableNum(InventItemGroupItem));
    qbds1.relations(true);

    qbds1.joinMode(JoinMode::InnerJoin);

    select ItemGroupId from parameter;

    qbr = qbds1.addRange(fieldNum(InventItemGroupItem,ItemGroupId));
    qbr.value(parameter.ItemGroupId);
    sysTableLookup.parmQuery(query);
    sysTableLookup.addLookupfield(fieldnum(InventTable, ItemId), true);
    sysTableLookup.addSelectionField(fieldNum(InventTable,Product));
    sysTableLookup.addLookupMethod(tableMethodStr(InventTable,defaultProductName));



    sysTableLookup.performFormLookup();
}