This article has been
excerpted from book "A Programmer's Guide to ADO.NET in C#".
The data adapter has a FillError event that occurs during a fill method. It
allows a user to determine whether a fill operation should continue. For
example, FillError could occur when you can't convert data from data from a
database to Common Language Runtime (CLR) type without losing precision or when
data type casting is not valid.
FillErrorEventHandler handles the FillError event. The event handler receives an
argument of type FillErrorEventArgs, which contains data related to this event.
The FillErrorEventHandler is as follows:
public
delegate void
FillErrorEventHandler(object
sender, FillErrorEventArgs e );
Where sender is the source of the event and e is FillErrorEventArgs, which
contains the event data. Table 9-3 defines the FillErrorEventArgs properties.
Table 9-3. The FillErrorEventArgs members
|
Property |
Description |
|
Continue |
Represent a value
indicating whether to continue the fill operator |
|
DataTable |
Return the data table
being updated when the error occurred |
|
Errors |
Returns the errors |
|
Values |
Returns the rows
being updated when error occurred |
RowUpdated and RowUpdating are two more events that a data adapter supports. The
RowUpdating event occurs when an Update method is called before a command
executed against the data source. The RowUpdated event occurs when a command
executed.
The RowUpdated event handler receives an argument of type
OleDbRowUpdatedEventArgs that contains data related to this event. Table 9-4
describes the OleDbRowUpdateEventArgs members.
Table 9-4. The OleDbRowUpdatedEventArgs Members
|
Property |
Description |
|
Command |
Returns the command
object executed when
Update
is called |
|
Errors |
Returns errors
generated during the update operation |
|
RecrodsAffected |
Returns the number of
rows affected during insert, update, and delete operations |
|
Row |
Returns the data row
sent through an
Update |
|
StatementType |
Returns the SQL
statement type |
|
Status |
Returns the
UpdateStatus of a command |
|
TableMapping |
Returns the
DataTableMapping
sent through an
Update |
Similar to RowUpdated, the RowUpdating event handler receives an argument of
type OleDbRowupdatingEventArgs that defines the same properties as
OleDbRowUpdated with the same meaning.
Ok, now it's time to write an application to test the data adapter events. I
created a Windows application and added a button control to the form. After that
I changed the button's name property to DataAdapterEventsTestBtn and wrote a
button-click event handler by double-clicking on the button control.
Next, I added a data adapter control to the form by dragging the
OleBbdAtaadapter component from the toolbox's data tab to the form. As you drop
the OleDbDataAdapter component to the form, the data adapter configuration
wizard pops up. In this application, I added the Customers table to the Query
Builder and selected the CompanyName, ContactName, and CustomerID columns from
the Customers table. As you can see from figure 9-8, the Query Builder shows the
SQL statement.
Figure 9-8. The query builder with the SELECT statement from the Customers
table
Next, I used the Properties > Event (the lightning bolt) button of the data
adapter to add the event handlers. I added all three FillError, RowUpdating and
RowUpdated event handlers, as shown in Figure 9-9.
Figure 9-9 AddingDataAdapter events from the Properties window
Now you can write code on the FillError event handler. You call the FillError
event handler when the Fill method of data adapter of data adapter fails.
Listing 9-3 shows the code for the FillError event handler. As you can see from
listing 9-3, I used DataFillErrorEventArgs's members to get information about
the error.
Listing 9-3. DataAdapter FillError event handler code
//FillError Event Handler
private void
oleDbDataAdapter1_FillError(object sender,
System.Data.FillErrorEventArgs e)
{
if (e.Errors.GetType() ==
typeof(System.OverflowException))
{
MessageBox.Show("Error
in Fill operation for table" +
e.DataTable.TableName +
",
Error Message: " + e.Errors.Message.ToString() +
", Source: " + e.Errors.Source.ToString());
e.Continue =
true;
}
}
Listing 9-4 and 9-5 show the code for the RowUpdated and RowUpdating event
handlers. You call the RowUpdated event handler when a row is updated using the
Update method of a data adapter, and you call RowUpdating when a row is
updating.
Listing 9-4. The RowUpdated event handler
// RowUpdated event handler
private void
oleDbDataAdapter1_RowUpdated(object sender,
System.Data.OleDb.OleDbRowUpdatedEventArgs e)
{
if (e.Status ==
UpdateStatus.ErrorsOccurred)
{
MessageBox.Show("Error
Message: " + e.Errors.Message.ToString() +
", Source: " + e.Errors.Source.ToString());
e.Row.RowError
= e.Errors.Message;
e.Status =
UpdateStatus.SkipCurrentRow;
}
else
{
MessageBox.Show("Updated");
}
}
As you can see from Listing 9-5, you can compare the StatementType member of
OleDbRowUpdatingEventArgs to the StatementType enumeration to find out the
statement type. The StatementType enumeration defines Select, Insert, Update,
and Delete members.
Listing 9-5, The RowUpdating event handler
private void
oleDbDataAdapter1_RowUpdating(object sender,
System.Data.OleDb.OleDbRowUpdatingEventArgs
e)
{
// Inserting
if (e.StatementType ==
StatementType.Insert)
{
MessageBox.Show("Inserting");
}
// Updating
else if
(e.StatementType == StatementType.Update)
{
MessageBox.Show("Updating");
}
//
Deleting
else if
(e.StatementType == StatementType.Delete)
{
MessageBox.Show("Deleting");
}
//Selecting
else if (e.StatementType
== StatementType.Select)
{
MessageBox.Show("Selecting");
}
}
Now, to test these events you can write code that fills a dataset and calls the
update method of data adapter. I added an event handler for the button by
double- clicking on it and writing the code shown in listing 9-6. As you can
see, I created a new OleDbDataAdapter object and copied oleDbDataAdapter1 to it
(the framework added oleDbDataAdapter1).
Listing 9-6.Calling DataAdapter's Fill and update methods
private void
DataAdapterEventsTestBtn_Click(object sender, System.EventArgs
e)
{
OleDbConnection
conn = new OleDbConnection();
string strDSN =
"Provider=Microsoft.Jet.OLEDB.4.0;" +
"Data Source=C:\\NorthWind.mdb";
conn.ConnectionString = strDSN;
OleDbDataAdapter
da = new OleDbDataAdapter();
da =
oleDbDataAdapter1;
// Creating InsertCommand
da.InsertCommand =
new OleDbCommand
("INSERT
INTO Customers(CustomerID,CompanyName)" +
"VALUES(?, ?)", conn);
da.InsertCommand.Parameters.Add
("@CustomerID",
OleDbType.VarChar, 5, "CustomerID");
da.InsertCommand.Parameters.Add
("@CompanyName",
OleDbType.VarChar, 30, "CompanyName");
// Opening Connection
conn.Open();
// Create and Fill DataSet
DataSet custDS = new
DataSet();
da.Fill(custDS,
"Customers");
// Add a new data row and call Update
method
// of data adapter
DataRow custRow = custDS.Tables["Customers"].NewRow();
custRow["CustomerID"]
= "NEWCO";
custRow["CompanyName"]
= "New Company";
custDS.Tables["Customers"].Rows.Add(custRow);
da.Update(custDS,
"Customers");
// Close the Connection
conn.Close();
}
Note: Don't forget to add a reference to the System.Data.OleDb namespace.
You can also use the SelectCommand, UpdateCommand, and DeleteCommand objects to
select, update, and delete date from the table.
Now, if you run the application, you'll see an insert message; if you click the
button more than once, you'll get the error shown in Figure 9-10.
Figure 9-10. The error message generated by the RowUpdated event handler when
trying to add duplicate employee records
Conclusion
Hope this article would have helped you in understanding
working with DataAadapter Events in ADO.NET.
See other articles on
the website also for further reference.
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