Creating several links between parts

Hello,

I need to create several WTPartUsageLinks with one part as parent and different parts as childs. I want to checkout parent part only once and I use code like that:

    String parentNumber = new String(parentNumber_param.getBytes(), "windows-1251");    QuerySpec qspecParent = new QuerySpec(WTPart.class);    qspecParent.appendWhere(new SearchCondition(WTPart.class, WTPart.NUMBER, SearchCondition.EQUAL, parentNumber), newint[] {0,1});    QueryResult qrParent = PersistenceHelper.manager.find((StatementSpec)qspecParent);    while (qrParent.hasMoreElements())    {      partParent = (WTPart)qrParent.nextElement();      if (partParent.isLatestIteration())                    break;    }    //some code skipped     Quantity wcQty = new Quantity();    wcQty.setAmount(qty);    wcQty.setUnit(qUnit);    WTPart checkedOutParent = null;    if (!WorkInProgressHelper.isCheckedOut(partParent))         checkedOutParent = (WTPart) WorkInProgressHelper.service.checkout(partParent, WorkInProgressHelper.service.getCheckoutFolder(), "checked out").getWorkingCopy();    else     {        if (!WorkInProgressHelper.isWorkingCopy(partParent))             checkedOutParent = (WTPart) WorkInProgressHelper.service.workingCopyOf(partParent);        else            checkedOutParent = partParent;     }     WTPartUsageLink link = WTPartUsageLink.newWTPartUsageLink(checkedOutParent, (WTPartMaster) partChild.getMaster());     link.setQuantity(wcQty);     PersistenceHelper.manager.save(link);     if (needsCheckIn)            WorkInProgressHelper.service.checkin(checkedOutParent, "");   

When I call this page for the first time, parent part checks out and a new link appears in Windchill client, but when parent part is already checked out

before, links don't appear after part checkin. But when I check out this part one more time in windchill cilent, I can see all the links created.

Can someone tell what is wrong with this code? Thanks in advance.