Update Default Financial Dimension in AX 2012 using X++ 

static void ABUDefaultFinancialDim_AP(Args _args)

{

    DimensionAttributeValue             dimAttrBUValue,dimAtrrCCValue,dimAtrrDepValue,dimAttrIGValue,dimAtrrProjValue;

    DimensionAttribute                  dimAttrBU,dimAtrrCC,dimAtrrDep,dimAttrIG,dimAtrrProj;

    DimensionAttributeValueSetStorage   davss;

    RecId                               defaultDimension;

    AssetBook                           Assetbook;

    AssetId                             AssetId;

    str                                 A_SITES, B_BRANCHES, C_DEPARTMENTS;

    SysExcelApplication         application;

    SysExcelWorkbooks           workbooks;

    SysExcelWorkbook            workbook;

    SysExcelWorksheets          worksheets;

    SysExcelWorksheet           worksheet;

    SysExcelCells               cells;

    COMVariantType              type1;

    Name                        name;

    HcmWorker                   HCMWorker;

    HcmPersonnelNumberId        HcmPersonnelNumberId;

    FileName                    filename;

    CustTable                   CustTable;

    CustAccount                 CustAccount;

    DirPartyName                DirPartyName;

    CustPriceGroup              PriceGroup;

    DirPartyTable               dirPartyTable1;

    LogisticsPostalAddress      postalAddress;

    LogisticsLocation           location;

    LogisticsLocationRole       locationRole;

    DirPartyLocationRole        partyLocationRole;

    DirPartyLocation            partyLocation;

    int                         row;

    str                         currency;

    str                         site,warehouse,payterid,paymode;

    str  100                    Address,Description;

    Dialog                      _dialog;

    DialogField                 _file;

     str COMVariant2Str(COMVariant _cv, int _decimals = 0,int _characters = 0,int _separator1 = 0,int _separator2 = 0)

       {

            switch(_cv.variantType())

            {

                case (COMVariantType::VT_BSTR):

                    return _cv.bStr();

                case (COMVariantType::VT_R4):

                    return num2str(_cv.float(),_characters,_decimals, _separator1,_separator2);

                case (COMVariantType::VT_R8):

                    return num2str(_cv.double(),_characters,_decimals,_separator1,_separator2);

                case (COMVariantType::VT_DECIMAL):

                    return num2str(_cv.decimal(),_characters,_decimals, _separator1, _separator2);

                case (COMVariantType::VT_DATE):

                    return date2str(_cv.date(),123,2,1,2, 1,4);

                case (COMVariantType::VT_EMPTY):

                    return "";

                default:

                    throw error(strfmt("@SYS26908",_cv.variantType()));

            }

            return "";

        }

    ;

    _dialog = new Dialog("Please select the file to load");

    _dialog.addText("Select file:");

    _file = _dialog.addField(ExtendedTypeStr("FilenameOpen"));

    _dialog.run();

    application = SysExcelApplication::construct();

    workbooks = application.workbooks();

    filename = _file.value();

    try

    {

        workbooks.open(filename);

    }

    catch (Exception::Error)

    {

        throw error("File cannot be opened.");

    }

    workbook = workbooks.item(1);

    worksheets = workbook.worksheets();

    worksheet = worksheets.itemFromNum(1);

    cells = worksheet.cells();

    row = 1;

    do

    {

        row++;

        Assetid                      = cells.item(row, 1).value().bStr();

        A_SITES                      = cells.item(row, 2).value().bStr();

        B_BRANCHES                   = cells.item(row, 3).value().bStr();

        C_DEPARTMENTS                = cells.item(row, 4).value().bStr();

       

        davss = DimensionAttributeValueSetStorage::find(AssetBook::find(Assetid, 'Commercial').DefaultDimension);

        dimAttrBU = DimensionAttribute::findByName('A_SITES');

        dimAtrrCC = DimensionAttribute::findByName('B_BRANCHES');

        dimAtrrDep = DimensionAttribute::findByName('C_DEPARTMENTS');

        dimAttrBUValue = DimensionAttributeValue::findByDimensionAttributeAndValue(dimAttrBU, A_SITES, false, true);

        dimAtrrCCValue = DimensionAttributeValue::findByDimensionAttributeAndValue(dimAtrrCC, B_BRANCHES, false, true);

        dimAtrrDepValue = DimensionAttributeValue::findByDimensionAttributeAndValue(dimAtrrDep, C_DEPARTMENTS, false, true);   

        if(dimAttrBUValue || dimAtrrCCValue ||dimAtrrDepValue)

        {

            ttsBegin;

            davss.addItem(dimAttrBUValue);

            davss.addItem(dimAtrrCCValue);

            davss.addItem(dimAtrrDepValue); 

       

            select forUpdate Assetbook where Assetbook.AssetId == Assetid;

            Assetbook.DefaultDimension = davss.save();

            Assetbook.update();

            ttsCommit;

           

            info(strFmt('Asset id %1 - DefaultDimension %2', AssetId, Assetbook.DefaultDimension));

        }

        type1 = cells.item(row+1, 1).value().variantType();

    }

    while (type1 != COMVariantType::VT_EMPTY);

    application.quit();

}

This is template for update DefaultDimension fixed Asset (AssetTable) :