How to Count(Sum) of Form in AX 2009

DataSource excuteQuery method
A) Support for multiple DataSources
B) Support the user to filter the data.
C) Support mass of data

smmBusRelTable.excuteQuery()
{...
    m_qrCount = new QueryRun(smmBusRelTable_ds.queryRun().query().pack());
    m_qbdsCount =   m_qrCount.query().dataSourceNo(1);
    m_qbdsCount.addSelectionField(fieldNum(smmBusRelTable,RecId),SelectionField::Count);
    while (m_qrCount.next())
    {
        m_count = any2int(m_qrCount.getNo(1).RecId);
    }
...
}