private bool m_ChangingFromEvent = false;

        private void SourceDataTable_ColumnChanging(object sender, DataColumnChangeEventArgs e)
        {
            if (m_ChangingFromEvent)
                return;
            m_ChangingFromEvent = true;
            try
            {
                OnColumnChanging(e);
            }
            finally
            {
                m_ChangingFromEvent = false;
            }
        }

        private void SourceDataTable_ColumnChanged(object sender, DataColumnChangeEventArgs e)
        {
            if (m_ChangingFromEvent)
                return;
            m_ChangingFromEvent = true;
            try
            {
                OnColumnChanged(e);
            }
            finally
            {
                m_ChangingFromEvent = false;
            }
        }

        private void SourceDataTable_RowDeleting(object sender, DataRowChangeEventArgs e)
        {
            if (m_ChangingFromEvent)
                return;
            m_ChangingFromEvent = true;
            try
            {
                OnRowDeleting(e);
            }
            finally
            {
                m_ChangingFromEvent = false;
            }
        }

        private void SourceDataTable_RowDeleted(object sender, DataRowChangeEventArgs e)
        {
            if (m_ChangingFromEvent)
                return;
            m_ChangingFromEvent = true;
            try
            {
                OnRowDeleted(e);
            }
            finally
            {
                m_ChangingFromEvent = false;
            }
        }

        private void SourceDataTable_RowChanging(object sender, DataRowChangeEventArgs e)
        {
            if (m_ChangingFromEvent)
                return;
            m_ChangingFromEvent = true;
            try
            {
                OnRowChanging(e);
            }
            finally
            {
                m_ChangingFromEvent = false;
            }
        }

        private void SourceDataTable_RowChanged(object sender, DataRowChangeEventArgs e)
        {
            if (m_ChangingFromEvent)
                return;

            m_ChangingFromEvent = true;
            try
            {
                if (e.Action == DataRowAction.Add || e.Action == DataRowAction.Change ||
                    (e.Action == DataRowAction.Rollback && e.Row.RowState == DataRowState.Unchanged))
                {

                    bool unchanged = e.Row.RowState == DataRowState.Unchanged;
                    e.Row.BeginEdit();
                    try
                    {
                        OnCalculateFields(e);
                        e.Row.EndEdit();
                    }
                    catch
                    {
                        e.Row.CancelEdit();
                        throw;
                    }
                    if (unchanged)
                        e.Row.AcceptChanges();
                }
                OnRowChanged(e);
            }
            finally
            {
                m_ChangingFromEvent = false;
            }
        }

        public event DataRowChangeEventHandler CalculateFields;
        protected virtual void OnCalculateFields(DataRowChangeEventArgs e)
        {
            if (CalculateFields != null)
                CalculateFields(this, e);
        }

class MyEntity
{
    public DateTime MyDate { get; set; }
    
    public int ElapsedMinutes
    {
        get { return (DateTime.Now - MyDate).TotalMinutes; }
    }
}