数据库中事务使用实例

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1.数据库的事务很重要，在保持数据一致性有很大的用处

USE [DNN ]
GO
/****** Object:  StoredProcedure [dbo].[aspnet_Membership_ResetPassword]    Script Date: 01/16/2015 11:05:36 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[aspnet_Membership_ResetPassword]
    @ApplicationName             nvarchar(256),
    @UserName                    nvarchar(256),
    @NewPassword                 nvarchar(128),
    @MaxInvalidPasswordAttempts  int,
    @PasswordAttemptWindow       int,
    @PasswordSalt                nvarchar(128),
    @CurrentTimeUtc              datetime,
    @PasswordFormat              int = 0,
    @PasswordAnswer              nvarchar(128) = NULL
AS
BEGIN
    DECLARE @IsLockedOut                            bit
    DECLARE @LastLockoutDate                        datetime
    DECLARE @FailedPasswordAttemptCount             int
    DECLARE @FailedPasswordAttemptWindowStart       datetime
    DECLARE @FailedPasswordAnswerAttemptCount       int
    DECLARE @FailedPasswordAnswerAttemptWindowStart datetime

    DECLARE @UserId                                 uniqueidentifier
    SET     @UserId = NULL

    DECLARE @ErrorCode     int
    SET @ErrorCode = 0

    DECLARE @TranStarted   bit
    SET @TranStarted = 0

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

    SELECT  @UserId = u.UserId
    FROM    dbo.aspnet_Users u, dbo.aspnet_Applications a, dbo.aspnet_Membership m
    WHERE   LoweredUserName = LOWER(@UserName) AND
            u.ApplicationId = a.ApplicationId  AND
            LOWER(@ApplicationName) = a.LoweredApplicationName AND
            u.UserId = m.UserId

    IF ( @UserId IS NULL )
    BEGIN
        SET @ErrorCode = 1
        GOTO Cleanup
    END

    SELECT @IsLockedOut = IsLockedOut,
           @LastLockoutDate = LastLockoutDate,
           @FailedPasswordAttemptCount = FailedPasswordAttemptCount,
           @FailedPasswordAttemptWindowStart = FailedPasswordAttemptWindowStart,
           @FailedPasswordAnswerAttemptCount = FailedPasswordAnswerAttemptCount,
           @FailedPasswordAnswerAttemptWindowStart = FailedPasswordAnswerAttemptWindowStart
    FROM dbo.aspnet_Membership WITH ( UPDLOCK )
    WHERE @UserId = UserId

    IF( @IsLockedOut = 1 )
    BEGIN
        SET @ErrorCode = 99
        GOTO Cleanup
    END

    UPDATE dbo.aspnet_Membership
    SET    Password = @NewPassword,
           LastPasswordChangedDate = @CurrentTimeUtc,
           PasswordFormat = @PasswordFormat,
           PasswordSalt = @PasswordSalt
    WHERE  @UserId = UserId AND
           ( ( @PasswordAnswer IS NULL ) OR ( LOWER( PasswordAnswer ) = LOWER( @PasswordAnswer ) ) )

    IF ( @@ROWCOUNT = 0 )
        BEGIN
            IF( @CurrentTimeUtc > DATEADD( minute, @PasswordAttemptWindow, @FailedPasswordAnswerAttemptWindowStart ) )
            BEGIN
                SET @FailedPasswordAnswerAttemptWindowStart = @CurrentTimeUtc
                SET @FailedPasswordAnswerAttemptCount = 1
            END
            ELSE
            BEGIN
                SET @FailedPasswordAnswerAttemptWindowStart = @CurrentTimeUtc
                SET @FailedPasswordAnswerAttemptCount = @FailedPasswordAnswerAttemptCount + 1
            END

            BEGIN
                IF( @FailedPasswordAnswerAttemptCount >= @MaxInvalidPasswordAttempts )
                BEGIN
                    SET @IsLockedOut = 1
                    SET @LastLockoutDate = @CurrentTimeUtc
                END
            END

            SET @ErrorCode = 3
        END
    ELSE
        BEGIN
            IF( @FailedPasswordAnswerAttemptCount > 0 )
            BEGIN
                SET @FailedPasswordAnswerAttemptCount = 0
                SET @FailedPasswordAnswerAttemptWindowStart = CONVERT( datetime, '17540101', 112 )
            END
        END

    IF( NOT ( @PasswordAnswer IS NULL ) )
    BEGIN
        UPDATE dbo.aspnet_Membership
        SET IsLockedOut = @IsLockedOut, LastLockoutDate = @LastLockoutDate,
            FailedPasswordAttemptCount = @FailedPasswordAttemptCount,
            FailedPasswordAttemptWindowStart = @FailedPasswordAttemptWindowStart,
            FailedPasswordAnswerAttemptCount = @FailedPasswordAnswerAttemptCount,
            FailedPasswordAnswerAttemptWindowStart = @FailedPasswordAnswerAttemptWindowStart
        WHERE @UserId = UserId

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

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

    RETURN @ErrorCode

Cleanup:

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

    RETURN @ErrorCode

END

2.事务会锁定数据库表在使用时一定要注意，查询语句加上不锁表

 SELECT @IsLockedOut = IsLockedOut,
           @LastLockoutDate = LastLockoutDate,
           @FailedPasswordAttemptCount = FailedPasswordAttemptCount,
           @FailedPasswordAttemptWindowStart = FailedPasswordAttemptWindowStart,
           @FailedPasswordAnswerAttemptCount = FailedPasswordAnswerAttemptCount,
           @FailedPasswordAnswerAttemptWindowStart = FailedPasswordAnswerAttemptWindowStart
    FROM dbo.aspnet_Membership WITH ( UPDLOCK )

  IF (EXISTS (SELECT *
                    FROM  dbo.aspnet_Membership m WITH ( UPDLOCK, HOLDLOCK )
                    WHERE ApplicationId = @ApplicationId AND LoweredEmail = LOWER(@Email)))