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Concurrency

ProgramVB
ProgramVB asked
on
Medium Priority
643 Views
Last Modified: 2010-04-17
Hi all, well im at the painful stage of moving to vb.NET from VB6 - and a little confused!!
What I want to know is how do I handle concurrency with ADO.NET. With ADO I used optimistic locking, if I got an error
from SQL Server then I knew that I had a lock etc, now I read that with ADO.NET we get a DataSet thats disconnected.
What I need to know is how does ADO.NET handle concurrency issues, ie, what when i go to write my disconnected
dataset to the database and I find someone else has changed the same fields while I was away with the Dataset??

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Commented:
SqlConnection nwindConn = new SqlConnection("Data Source=localhost;Integrated Security=SSPI;Initial Catalog=northwind");

 SqlDataAdapter custDA = new SqlDataAdapter("SELECT CustomerID, CompanyName FROM Customers ORDER BY CustomerID", nwindConn);

  // The Update command checks for optimistic concurrency violations in the WHERE clause.
  custDA.UpdateCommand = new SqlCommand("UPDATE Customers (CustomerID, CompanyName) VALUES(@CustomerID, @CompanyName) " +
                                        "WHERE CustomerID = @oldCustomerID AND CompanyName = @oldCompanyName", nwindConn);
  custDA.UpdateCommand.Parameters.Add("@CustomerID", SqlDbType.NChar, 5, "CustomerID");
  custDA.UpdateCommand.Parameters.Add("@CompanyName", SqlDbType.NVarChar, 30, "CompanyName");

  // Pass the original values to the WHERE clause parameters.
  SqlParameter myParm;
  myParm = custDA.UpdateCommand.Parameters.Add("@oldCustomerID", SqlDbType.NChar, 5, "CustomerID");
  myParm.SourceVersion = DataRowVersion.Original;
  myParm = custDA.UpdateCommand.Parameters.Add("@oldCompanyName", SqlDbType.NVarChar, 30, "CompanyName");
  myParm.SourceVersion = DataRowVersion.Original;

  // Add the RowUpdated event handler.
  custDA.RowUpdated += new SqlRowUpdatedEventHandler(OnRowUpdated);

  DataSet custDS = new DataSet();
  custDA.Fill(custDS, "Customers");

  // Modify the DataSet contents.

  custDA.Update(custDS, "Customers");

  foreach (DataRow myRow in custDS.Tables["Customers"].Rows)
  {
    if (myRow.HasErrors)
      Console.WriteLine(myRow[0] + "\n" + myRow.RowError);
  }


protected static void OnRowUpdated(object sender, SqlRowUpdatedEventArgs args)
{
  if (args.RecordsAffected == 0)
  {
    args.Row.RowError = "Optimistic Concurrency Violation Encountered";
    args.Status = UpdateStatus.SkipCurrentRow;
  }
}

Author

Commented:
AlexFM, the code looks great but could you explain a little whats happening

Author

Commented:
im also using VB not C#
Commented:
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