使用快照隔离snapshot isolation实例（二）

示例

以下示例演示修改数据时的快照隔离行为。该代码执行下列操作：

• 连接到 AdventureWorks 示例数据库并启用 SNAPSHOT 隔离。

• 创建一个名为 TestSnapshotUpdate 的表并插入三行示例数据。

• 使用 SNAPSHOT 隔离开始但是不完成 sqlTransaction1。在事务中选择三行数据。

• 创建第二个与 AdventureWorks 的 SqlConnection，并使用 READ COMMITTED 隔离级别创建第二个事务，更新在 sqlTransaction1 中选择的其中一行的值。

• 提交 sqlTransaction2。

• 返回 sqlTransaction1 并尝试更新 sqlTransaction2 已提交的相同的行。将引发 3960 错误，sqlTransaction1 将自动回滚。控制台窗口中将显示 SqlException.Number 和 SqlException.Message。

• 执行清理代码以禁用 AdventureWorks 中的快照隔离并删除 TestSnapshotUpdate 表。

View Code

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Data.SqlClient;

using System.Data;

namespace snapshot2

{

    class Program

    {

        static void Main(string[] args)

        {

            string connectionString = @"Data Source=XUWEI/SQLEXPRESS;Initial Catalog=AdventureWorks;User ID=sa;Password=sa12345";

            using (SqlConnection connection1 = new SqlConnection(connectionString))

            {

                connection1.Open();

                SqlCommand command1 = connection1.CreateCommand();

                // Enable Snapshot isolation in AdventureWorks，设置数据库使其支持快照隔离(Snapshot isolation)技术。

                command1.CommandText =

                    "ALTER DATABASE AdventureWorks SET ALLOW_SNAPSHOT_ISOLATION ON";

                try

                {

                    command1.ExecuteNonQuery();

                    Console.WriteLine(

                        "Snapshot Isolation turned on in AdventureWorks.");

                }

                catch (Exception ex)

                {

                    Console.WriteLine("ALLOW_SNAPSHOT_ISOLATION ON failed: {0}", ex.Message);

                }

                // Create a table ，创建表格。

                command1.CommandText =

                    "IF EXISTS "

                    + "(SELECT * FROM sys.tables "

                    + "WHERE name=N'TestSnapshotUpdate')"

                    + " DROP TABLE TestSnapshotUpdate";

                command1.ExecuteNonQuery();

                command1.CommandText =

                    "CREATE TABLE TestSnapshotUpdate "

                    + "(ID int primary key, CharCol nvarchar(100));";

                try

                {

                    command1.ExecuteNonQuery();

                    Console.WriteLine("TestSnapshotUpdate table created.");

                }

                catch (Exception ex)

                {

                    Console.WriteLine("CREATE TABLE failed: {0}", ex.Message);

                }

                // Insert some data，在表中创建数据。

                command1.CommandText =

                    "INSERT INTO TestSnapshotUpdate VALUES (1,N'abcdefg');"

                    + "INSERT INTO TestSnapshotUpdate VALUES (2,N'hijklmn');"

                    + "INSERT INTO TestSnapshotUpdate VALUES (3,N'opqrstuv');";

                try

                {

                    command1.ExecuteNonQuery();

                    Console.WriteLine("Data inserted TestSnapshotUpdate table.");

                }

                catch (Exception ex)

                {

                    Console.WriteLine(ex.Message);

                }

                // Begin, but do not complete, a transaction 

                // using the Snapshot isolation level.

                /*开始但不完成一个在快照隔离级别上的事务，

                 */

                SqlTransaction transaction1 = null;

                try

                {

                    transaction1 = connection1.BeginTransaction(IsolationLevel.Snapshot);

                    command1.CommandText =

                        "SELECT * FROM TestSnapshotUpdate WHERE ID BETWEEN 1 AND 3";

                    command1.Transaction = transaction1;

                    command1.ExecuteNonQuery();

                    Console.WriteLine("Snapshot transaction1 started.");

                    // Open a second Connection/Transaction to update data

                    // using ReadCommitted. This transaction should succeed.

                    /*打开第二个数据库连接，并创建一个在ReadCommitted上更新数据的事务。

                     * 这个事务能够成功。 

                     */

                    using (SqlConnection connection2 = new SqlConnection(connectionString))

                    {

                        connection2.Open();

                        SqlCommand command2 = connection2.CreateCommand();

                        command2.CommandText = "UPDATE TestSnapshotUpdate SET CharCol="

                            + "N'New value from Connection2' WHERE ID=1";

                        SqlTransaction transaction2 =

                            connection2.BeginTransaction(IsolationLevel.ReadCommitted);

                        command2.Transaction = transaction2;

                        try

                        {

                            command2.ExecuteNonQuery();

                            transaction2.Commit();//提交事务2

                            Console.WriteLine(

                                "transaction2 has modified data and committed.");

                        }

                        catch (SqlException ex)

                        {

                            Console.WriteLine(ex.Message);

                            transaction2.Rollback();

                        }

                        finally

                        {

                            transaction2.Dispose();

                        }

                    }

                    // Now try to update a row in Connection1/Transaction1.

                    // This transaction should fail because Transaction2

                    // succeeded in modifying the data.

                    /*试图更新连接1和事务1中的一行数据。这个事务执行失败，

                     * 这是因为在事务2中已经成功修改了数据。

                     * 事务1将自动回滚。

                     */

                    command1.CommandText =

                        "UPDATE TestSnapshotUpdate SET CharCol="

                        + "N'New value from Connection1' WHERE ID=1";

                    command1.Transaction = transaction1;

                    command1.ExecuteNonQuery();

                    transaction1.Commit();

                    Console.WriteLine("You should never see this.");//正常执行情况下应该不会再控制台中输出此句。

                }

                catch (SqlException ex)

                {

                    Console.WriteLine("Expected failure for transaction1:");

                    Console.WriteLine("  {0}: {1}", ex.Number, ex.Message);

                }

                finally

                {

                    transaction1.Dispose();

                }

            }

            // CLEANUP:清理程序

            // Turn off Snapshot isolation and delete the table

            using (SqlConnection connection3 = new SqlConnection(connectionString))

            {

                connection3.Open();

                SqlCommand command3 = connection3.CreateCommand();

                command3.CommandText =

                    "ALTER DATABASE AdventureWorks SET ALLOW_SNAPSHOT_ISOLATION OFF";

                try

                {

                    command3.ExecuteNonQuery();

                    Console.WriteLine(

                        "CLEANUP: Snapshot isolation turned off in AdventureWorks.");

                }

                catch (Exception ex)

                {

                    Console.WriteLine("CLEANUP FAILED: {0}", ex.Message);

                }

                command3.CommandText = "DROP TABLE TestSnapshotUpdate";

                try

                {

                    command3.ExecuteNonQuery();

                    Console.WriteLine("CLEANUP: TestSnapshotUpdate table deleted.");

                }

                catch (Exception ex)

                {

                    Console.WriteLine("CLEANUP FAILED: {0}", ex.Message);

                }

            }

        }

    }

}