Tài liệu Raising and Handling Stored Procedure Errors pptx

[ Team LiB ]


Recipe 2.10 Raising and Handling Stored Procedure Errors
Problem
You want to catch and handle an error raised from a stored procedure.
Solution
Use a try . . . catch block to catch serious errors. Use the SqlConnection.InfoMessage
event handler to catch informational and warning messages.
The sample code, as shown in Example 2-11
, uses a single stored procedure and two
event handlers:
SP0210_Raiserror
Accepts two input parameters specifying the severity and the state of an error and
raises an error with the specified severity and state.
Raise Error Button.Click
Creates a connection and attaches a handler for warning and information messages
from the SQL Server. A Command is created for the SP0210_Raiserror stored
procedure and the input parameters are defined. The user-specified severity and
state are assigned to the input parameters and the stored procedure command is
executed within a try statement.
SqlConnection.InfoMessage
Called when a warning or informational message is raised by the SQL Server.
Example 2-11. Stored procedure: SP0210_Raiserror
CREATE PROCEDURE SP0210_Raiserror
@Severity int,
@State int = 1
AS
if @Severity>=0 and @Severity <=18
RAISERROR ('Error of severity %d raised from SP 0210_Raiserror.', @Severity,
@State, @Severity)

if @Severity>=19 and @Severity<=25
RAISERROR ('Fatal error of severity %d raised from SP 0210_Raiserror.',
@Severity, @State, @Severity) WITH LOG

RETURN
The C# code is shown in Example 2-12
.
Example 2-12. File: RaiserrorForm.cs
// Namespaces, variables, and constants
using System;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;

// . . .

private void raiseErrorButton_Click(object sender, System.EventArgs e)
{
resultTextBox.Text =
"Severity: " + severityTextBox.Text + Environment.NewLine +
"State: " + stateTextBox.Text + Environment.NewLine +
Environment.NewLine;

// Create the connection.
SqlConnection conn = new SqlConnection(
ConfigurationSettings.AppSettings["Sql_ConnectString"]);
// Attach handler for SqlInfoMessage events.
conn.InfoMessage += new SqlInfoMessageEventHandler(conn_InfoMessage);

// Define a stored procedure command and the parameters.
SqlCommand cmd = new SqlCommand("SP0210_Raiserror", conn);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add("@Severity", SqlDbType.Int);
cmd.Parameters.Add("@State", SqlDbType.Int);
// Set the value for the stored procedure parameters.
cmd.Parameters["@Severity"].Value = severityTextBox.Text;
cmd.Parameters["@State"].Value = stateTextBox.Text;

// Open the connection.
conn.Open( );
try
{
// Try to execute the stored procedure.
cmd.ExecuteNonQuery( );
}
catch(System.Data.SqlClient.SqlException ex)
{
// Catch SqlException errors.
resultTextBox.Text += "ERROR: " + ex.Message;
}
catch(Exception ex)
{
// Catch other errors.
resultTextBox.Text += "OTHER ERROR: " + ex.Message;
}
finally
{
// Close the connection.
conn.Close( );

}
}

private void conn_InfoMessage(object sender, SqlInfoMessageEventArgs e)
{
resultTextBox.Text += "MESSAGE: " + e.Message;
}
Discussion
Errors and messages are returned from a SQL Server stored procedure to a calling
application using the RAISERROR (note the spelling) function. The error message
severity levels are listed in Table 2-12
.
Table 2-12. RAISERROR error message severity levels
Severity level Description
0-10 Informational
11-16 Error which can be corrected by the user
17-19 Resource or system error
20-25 Fatal error indicating a system problem
Severity levels greater than 20 result in the connection being closed.
Since severity levels 10 or less are considered to be informational, they raise a
SqlInfoMessageEvent rather than an error. This is handled by subscribing a
SqlInfoMessageEventHandler to the InfoMessage event of the SqlConnection object.
If the error has severity level 11 or greater, a SqlException is thrown by the SQL Server
.NET data provider.
For more information about the RAISERROR function, look up RAISERROR in SQL
Server Books Online.

[ Team LiB ]