Tài liệu Nesting Manual Transactions with the SQL Server .NET Data Provider ppt

[ Team LiB ]Recipe 6.3 Nesting Manual Transactions with the SQL Server .NET Data Provider Problem You need to create a nested transaction using the SQL Server .NET data provider, but th

[ Team LiB ]

Recipe 6.3 Nesting Manual Transactions with the SQL Server NET Data Provider Problem

You need to create a nested transaction using the SQL Server NET data provider, but the Begin( ) command that you need is only available with the OLE DB NET data provider The SQL Server data provider appears to provide no built-in support for nested

transactions You want to nest transactions when using it

Solution

Simulate nested transactions with savepoints when using the SQL Server NET data provider, manage and control the lifetime of the SqlTransaction class, and create the required exception handling

The sample code contains two event handlers:

Form.Load

Sets up the sample by filling a DataTable with the Categories table from the

Northwind sample database The default view of the table is bound to a data grid

on the form

Insert Button.Click

Inserts user-entered data for two Categories records into the Northwind database within a manual transaction A savepoint is created if the first record insert

succeeds If the insert of the second record fails, the transaction is rolled back to the savepoint and the first record insert is committed; otherwise, both record inserts are committed

The C# code is shown in Example 6-4

Example 6-4 File: NestedManualTransactionForm.cs

// Namespaces, variables, and constants

using System;

using System.Configuration;

using System.Windows.Forms;

using System.Data;

using System.Data.SqlClient;

private const String CATEGORIES_TABLE = "Categories";

private DataTable dt;

private SqlDataAdapter da;

//

private void NestedTransactionForm_Load(object sender, System.EventArgs e) {

// Fill the categories table

String sqlText = "SELECT CategoryID, CategoryName, " +

"Description FROM Categories";

da = new SqlDataAdapter(sqlText,

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

dt = new DataTable(CATEGORIES_TABLE);

da.FillSchema(dt, SchemaType.Source);

da.Fill(dt);

// Bind the default view of the table to the grid

dataGrid.DataSource = dt.DefaultView;

}

private void insertButton_Click(object sender, System.EventArgs e)

{

String sqlText = "INSERT " + CATEGORIES_TABLE + " "+

"(CategoryName, Description) VALUES " +

"(@CategoryName, @Description)";

// Create the connection

SqlConnection conn = new SqlConnection(

ConfigurationSettings.AppSettings["Sql_ConnectString"]);

// Create the transaction

conn.Open( );

SqlTransaction tran = conn.BeginTransaction( );

// Create command in the transaction with parameters

SqlCommand cmd = new SqlCommand(sqlText, conn, tran);

cmd.Parameters.Add(new SqlParameter("@CategoryName",

SqlDbType.NVarChar, 15));

cmd.Parameters.Add(new SqlParameter("@Description",

SqlDbType.NVarChar, 100));

try

{

// Insert the records into the table

if (categoryName1TextBox.Text.Trim( ).Length == 0)

// If CategoryName is empty, make it null (invalid)

cmd.Parameters["@CategoryName"].Value = DBNull.Value; else

cmd.Parameters["@CategoryName"].Value =

categoryName1TextBox.Text;

cmd.Parameters["@Description"].Value =

description1TextBox.Text;

cmd.ExecuteNonQuery( );

}

catch (Exception ex)

{

// Exception occurred Roll back the transaction

tran.Rollback( );

MessageBox.Show(ex.Message + Environment.NewLine + "Transaction rollback (records 1 and 2).");

conn.Close( );

return;

}

tran.Save("SavePoint1");

try

{

// Insert the records into the table

if (categoryName2TextBox.Text.Trim( ).Length == 0)

// If CategoryName is empty, make it null (invalid)

cmd.Parameters["@CategoryName"].Value = DBNull.Value; else

cmd.Parameters["@CategoryName"].Value =

categoryName2TextBox.Text;

cmd.Parameters["@Description"].Value =

description2TextBox.Text;

cmd.ExecuteNonQuery( );

// If okay to here, commit the transaction

tran.Commit( );

MessageBox.Show("Transaction committed (records 1 and 2)."); }

catch (SqlException ex)

{

tran.Rollback("SavePoint1");

tran.Commit( );

MessageBox.Show(ex.Message + Environment.NewLine +

"Transaction commit (record 1)." + Environment.NewLine +

"Transaction rollback (record 2).");

}

finally

{

conn.Close( );

}

// Refresh the data

da.Fill(dt);

}

Discussion

The OLE DB NET data provider's transaction class OleDbTransaction has a Begin( ) method that is used to initiate a nested transaction A nested transaction allows part of a transaction to be rolled back without rolling back the entire transaction An

InvalidOperationException is raised if the OLE DB data source does not support nested transactions

The SQL Server NET data provider's transaction class SqlTransaction does not have a Begin( ) method to initiate a nested transaction Instead, it has a Save( ) method that creates a savepoint in the transaction that can later be used to roll back a portion of the transaction—to the savepoint rather than rolling back to the start of the transaction The savepoint is named using the only argument of the Save( ) method An overload of the Rollback( ) method of the SqlTransaction class accepts an argument that you can use to specify the name of the savepoint to roll back to

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