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我有以下表格：回复和消息。我想模仿 Facebook 的行为：当一条消息被删除时，所有相关的回复也会被删除。我的表如下所示：

REPLIES
messageId                               replyId
6b61d107-dff3-4374-a3a2-75ac7478a2f2    865c873d-0210-482a-b8bd-371c4f07f0cf

MESSAGES
id                                      body
865c873d-0210-482a-b8bd-371c4f07f0cf    this is the reply
6b61d107-dff3-4374-a3a2-75ac7478a2f2    this is the message

我创建了一个第一个触发器，它可以在删除消息时删除回复中的相关行。我现在想创建另一个触发器，它会在每次删除回复中的一行时删除相关消息。现在回复变成了他们自己的消息，这是没有意义的。这是第二个触发器：

CREATE TRIGGER TRG_DEL_MESSAGES
ON Replies
FOR DELETE
AS
DELETE FROM Messages WHERE id = (SELECT replyId FROM DELETED)

当我尝试删除某些内容时会带来以下错误：

Maximum stored procedure, function, trigger, or view nesting level exceeded (limit 32).

显然有一个无限循环，我认为这是因为 DELETED 表被第一个触发器的数据填充（这引发了第二个）。但我真的不确定，我会很感激一些帮助。谢谢！

4

3 回答 3

1

像这样的东西对你有用吗？只需在消息上使用单个触发器即可删除递归，该触发器会预先计算所有相关消息，因此您应该最多获得一个嵌套调用？它从消息和回复中删除所有相关消息

CREATE TRIGGER TRG_DEL_REPLIES
ON [Messages]
FOR DELETE
AS
BEGIN
    DECLARE @Related TABLE (MessageId uniqueidentifier)

    --get all related messages so that we don't recurse
    BEGIN
        WITH AllReplies (MessageId)
        AS
        (
            --Anchor
            SELECT  D.MessageId
            FROM    Deleted D
            UNION ALL
            --Recurse
            SELECT  R.ReplyId
            FROM    AllReplies AR
            JOIN    Replies R
                    ON AR.MessageId = R.MessageId
        )
        INSERT  INTO @Related
        SELECT  * 
        FROM    AllReplies
    END

    --delete the replies

    DELETE  R
    FROM    Replies R
    JOIN    @Related REL
            ON R.MessageId = REL.MessageId

    --delete the messages

    DELETE  M
    FROM    [Messages] M
    JOIN    @Related REL
            ON  REL.MessageId = M.MessageId 
    LEFT
    JOIN    DELETED D
            ON REL.MessageId = D.MessageId
    WHERE   D.MessageId IS NULL
END

要将其转换为您想要的存储过程，我会这样做，而不是执行多个单独删除的循环：

CREATE PROCEDURE DeleteMessageWithReplies(@messageId uniqueidentifier)
AS
BEGIN
    DECLARE @Related TABLE (MessageId uniqueidentifier)

    --get all related messages
    BEGIN
        WITH AllReplies (MessageId)
        AS
        (
            --Anchor
            SELECT  @messageId
            UNION ALL
            --Recurse
            SELECT  R.ReplyId
            FROM    AllReplies AR
            JOIN    Replies R
                    ON AR.MessageId = R.MessageId
        )
        INSERT  INTO @Related
        SELECT  * 
        FROM    AllReplies
    END

    --delete the replies

    DELETE  R
    FROM    Replies R
    JOIN    @Related REL
            ON R.MessageId = REL.MessageId

    --delete the messages that haven't already been deleted

    DELETE  M
    FROM    [Messages] M
    JOIN    @Related REL
            ON  REL.MessageId = M.MessageId 
END
于 2012-12-10T13:59:53.643 回答
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感谢您的帮助弗格斯，我很感激。但是，正如@Ben 指出的那样，存储过程更容易编码。这是我刚刚写的，它可能会有所改进，但至少它有效。

EXEC('CREATE PROCEDURE deleteMessageWithReplies(@messageId uniqueidentifier)
AS
BEGIN
    DECLARE @repliesCount int
    SELECT @repliesCount = (SELECT COUNT(*) FROM Replies WHERE messageId=@messageId)
    DECLARE @cpt int
SET @cpt = 0
DELETE FROM Messages WHERE id = @messageId
WHILE @cpt < @repliesCount
BEGIN
    DECLARE @replyId uniqueidentifier
    SELECT @replyId = (SELECT TOP 1 replyId FROM Replies WHERE messageId=@messageId)
    DELETE FROM Replies WHERE replyId = @replyId
    DELETE FROM Messages WHERE id=@replyId
    SET @cpt = @cpt+1
END
END')
于 2012-12-10T14:12:22.170 回答
0

我建议要么按照 Fergus Bown 的建议在触发器中一次生成所有删除，要么将删除逻辑移动到存储过程调用。在我们的应用程序中，我们对所有 CRUD 操作（创建、读取、更新、删除）使用存储过程方法。

缺点是新手支持 DBA 如果他们使用 SQL 删除单个回复而不删除与之关联的所有其他消息，他们可能会犯错。但是这样的 DBA 应该知道改用存储过程（或者首先获得正确的 SQL）。

于 2012-12-10T14:16:43.583 回答