Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

in the RowError property of the corresponding row. The batch updateprocess continues with subsequent rows.• Last-win Your change is applied regardless of the current status of therow. To implement this approach, you have only to ensure that the SQLcommand used to carry the update is not too restrictive to generate adata conflict. A data conflict occurs when the SQL command finds norow to affect. If you build the SQL command so that it updates or deletesrows that match a primary key field, no data conflict will ever be raised.Conflict-aware SQL code is code generated by ADO.NET commandbuilders in which the WHERE clause ensures that the current status andthe original status of the row match prior to proceeding with thestatement.• Ask-the-user Take this route when neither of the two preceding optionswill work in all possible cases you foresee handling. By default, a dataconflict raises a DBConcurrencyException exception. This exception isnot raised if you set the ContinueUpdateOnError property to true. TheRow property of the exception class returns a reference to the row inerror. By reading the properties of such a DataRow object, you haveaccess to both proposed and original values. You have no access to theunderlying value, but you can obtain that value by issuing another queryagainst the database. Resolving the conflict ultimately means optingeither for a first-win or a last-win approach, but you let the user decidewhich. Your goal is to provide the user with enough information to makethe correct choice.The following code uses the "ask-the-user" approach for resolving update dataconflicts:OleDbDataAdapter da = new OleDbDataAdapter();da.ContinueUpdateOnError = true;da.SelectCommand = new OleDbCommand("SELECT * FROM employees",m_conn);OleDbCommandBuilder cb = new OleDbCommandBuilder(da);da.Update(m_dataSet, "Employees");Figure 10-10 shows the sample application when a change fails.384