aspnet_Membership_CreateUser 为什么活动事务不为0的时候不开始事务

問題描述：

使用ASP.NET 2.0 成员资格/角色模型需要在SQL SERVER数据库中创建若干个以"aspnet_"开头的数据表,在处理这些数据表的时候也用到了不少的存储过程,在这些存储过程中,我发现有好几个存储过程都用到了以下的代码:

IF( @@TRANCOUNT = 0 )
    BEGIN
        BEGIN TRANSACTION
        SET @TranStarted = 1
    END
    ELSE
        SET @TranStarted = 0

通过查询MSDN我知道, @@TRANCOUNT是一个全局变量, 存储着当前连接活动的事务数.

但问题是, 为什么当前存在活动的事务的时候就要BEGIN TRANSACTION
而不存在活动事务的时候就不需要 设置一个显式事物的起点呢?

以下是aspnet_Membership_CreateUser存储过程的定义:

CREATE PROCEDURE [dbo].[aspnet_Membership_CreateUser]
    @ApplicationName                        nvarchar(256),
    @UserName                               nvarchar(256),
    @Password                               nvarchar(128),
    @PasswordSalt                           nvarchar(128),
    @Email                                  nvarchar(256),
    @PasswordQuestion                       nvarchar(256),
    @PasswordAnswer                         nvarchar(128),
    @IsApproved                             bit,
    @CurrentTimeUtc                         datetime,
    @CreateDate                             datetime = NULL,
    @UniqueEmail                            int      = 0,
    @PasswordFormat                         int      = 0,
    @UserId                                 uniqueidentifier OUTPUT
AS
BEGIN
    DECLARE @ApplicationId uniqueidentifier
    SELECT  @ApplicationId = NULL

    DECLARE @NewUserId uniqueidentifier
    SELECT @NewUserId = NULL

    DECLARE @IsLockedOut bit
    SET @IsLockedOut = 0

    DECLARE @LastLockoutDate  datetime
    SET @LastLockoutDate = CONVERT( datetime, '17540101', 112 )

    DECLARE @FailedPasswordAttemptCount int
    SET @FailedPasswordAttemptCount = 0

    DECLARE @FailedPasswordAttemptWindowStart  datetime
    SET @FailedPasswordAttemptWindowStart = CONVERT( datetime, '17540101', 112 )

    DECLARE @FailedPasswordAnswerAttemptCount int
    SET @FailedPasswordAnswerAttemptCount = 0

    DECLARE @FailedPasswordAnswerAttemptWindowStart  datetime
    SET @FailedPasswordAnswerAttemptWindowStart = CONVERT( datetime, '17540101', 112 )

    DECLARE @NewUserCreated bit
    DECLARE @ReturnValue   int
    SET @ReturnValue = 0

    DECLARE @ErrorCode     int
    SET @ErrorCode = 0

    DECLARE @TranStarted   bit
    SET @TranStarted = 0

    --就是这里, 鄙人感到很困惑...
    IF( @@TRANCOUNT = 0 )
    BEGIN
        BEGIN TRANSACTION
        SET @TranStarted = 1
    END
    ELSE
        SET @TranStarted = 0

    EXEC dbo.aspnet_Applications_CreateApplication @ApplicationName, @ApplicationId OUTPUT

    IF( @@ERROR <> 0 )
    BEGIN
        SET @ErrorCode = -1
        GOTO Cleanup
    END

    SET @CreateDate = @CurrentTimeUtc

    SELECT  @NewUserId = UserId FROM dbo.aspnet_Users WHERE LOWER(@UserName) = LoweredUserName AND @ApplicationId = ApplicationId
    IF ( @NewUserId IS NULL )
    BEGIN
        SET @NewUserId = @UserId
        EXEC @ReturnValue = dbo.aspnet_Users_CreateUser @ApplicationId, @UserName, 0, @CreateDate, @NewUserId OUTPUT
        SET @NewUserCreated = 1
    END
    ELSE
    BEGIN
        SET @NewUserCreated = 0
        IF( @NewUserId <> @UserId AND @UserId IS NOT NULL )
        BEGIN
            SET @ErrorCode = 6
            GOTO Cleanup
        END
    END

    IF( @@ERROR <> 0 )
    BEGIN
        SET @ErrorCode = -1
        GOTO Cleanup
    END

    IF( @ReturnValue = -1 )
    BEGIN
        SET @ErrorCode = 10
        GOTO Cleanup
    END

    IF ( EXISTS ( SELECT UserId
                  FROM   dbo.aspnet_Membership
                  WHERE  @NewUserId = UserId ) )
    BEGIN
        SET @ErrorCode = 6
        GOTO Cleanup
    END

    SET @UserId = @NewUserId

    IF (@UniqueEmail = 1)
    BEGIN
        IF (EXISTS (SELECT *
                    FROM  dbo.aspnet_Membership m WITH ( UPDLOCK, HOLDLOCK )
                    WHERE ApplicationId = @ApplicationId AND LoweredEmail = LOWER(@Email)))
        BEGIN
            SET @ErrorCode = 7
            GOTO Cleanup
        END
    END

    IF (@NewUserCreated = 0)
    BEGIN
        UPDATE dbo.aspnet_Users
        SET    LastActivityDate = @CreateDate
        WHERE  @UserId = UserId
        IF( @@ERROR <> 0 )
        BEGIN
            SET @ErrorCode = -1
            GOTO Cleanup
        END
    END

    INSERT INTO dbo.aspnet_Membership
                ( ApplicationId,
                  UserId,
                  Password,
                  PasswordSalt,
                  Email,
                  LoweredEmail,
                  PasswordQuestion,
                  PasswordAnswer,
                  PasswordFormat,
                  IsApproved,
                  IsLockedOut,
                  CreateDate,
                  LastLoginDate,
                  LastPasswordChangedDate,
                  LastLockoutDate,
                  FailedPasswordAttemptCount,
                  FailedPasswordAttemptWindowStart,
                  FailedPasswordAnswerAttemptCount,
                  FailedPasswordAnswerAttemptWindowStart )
         VALUES ( @ApplicationId,
                  @UserId,
                  @Password,
                  @PasswordSalt,
                  @Email,
                  LOWER(@Email),
                  @PasswordQuestion,
                  @PasswordAnswer,
                  @PasswordFormat,
                  @IsApproved,
                  @IsLockedOut,
                  @CreateDate,
                  @CreateDate,
                  @CreateDate,
                  @LastLockoutDate,
                  @FailedPasswordAttemptCount,
                  @FailedPasswordAttemptWindowStart,
                  @FailedPasswordAnswerAttemptCount,
                  @FailedPasswordAnswerAttemptWindowStart )

    IF( @@ERROR <> 0 )
    BEGIN
        SET @ErrorCode = -1
        GOTO Cleanup
    END

    IF( @TranStarted = 1 )
    BEGIN
        SET @TranStarted = 0
        COMMIT TRANSACTION
    END

    RETURN 0

Cleanup:

    IF( @TranStarted = 1 )
    BEGIN
        SET @TranStarted = 0
        ROLLBACK TRANSACTION
    END

    RETURN @ErrorCode

END

 

 

問題解答：

當在執行那個存儲過程之前也有其他事務正在進行，沒有結束。
如果執行了完那個存儲過程之後，其他事務進行回滾操作，那麼就會連帶着那個存儲過程的所有修改都會進行回滾操作。看看下面的代碼就會明白了：

-- 如果在執行那個存儲過程之前,设置一个显式事物的起点
BEGIN TRANSACTION

DECLARE    @return_value int,
        @UserId uniqueidentifier,
        @CurrentTime datetime
SET @CurrentTime = GETDATE()

EXEC    @return_value = [dbo].[aspnet_Membership_CreateUser]
        @ApplicationName = 'Teaching',
        @UserName = 'hang',
        @Password = 'asDF12#$',
        @PasswordSalt = 'qw#45&!t',
        @Email = '[email protected]',
        @PasswordQuestion = 'who are you?',
        @PasswordAnswer = 'hang',
        @IsApproved = 1,
        @CurrentTimeUtc = @CurrentTime,
        @CreateDate = @CurrentTime,
        @UniqueEmail = 0,
        @PasswordFormat = 1,
        @UserId = @UserId OUTPUT

SELECT    @UserId as N'@UserId'

SELECT    'Return Value' = @return_value

GO

-- 執行存儲過程完畢

-- 假如執行完那個存儲過程之後執行ROLLBACK操作
-- 那麼之前執行的存儲過程的所有修改都會得到回滾
ROLLBACK TRANSACTION