Question

我的数据库中有两个表，一个记录异常，另一个表记录日志消息。

我正在利用SqlDependency对象在这些表发生更改时收到通知，以便我可以更新我的Web仪表板。我得到了这个工作：

public IEnumerable<ElmahException> GetExceptions()
    {
        using (var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["elmah-sqlserver"].ConnectionString))
        {
            connection.Open();
            using (SqlCommand command = new SqlCommand(@"SELECT [ErrorId],[Application],[Host],[Type],[Source],[Message],[User],[StatusCode],[TimeUtc],[Sequence],[AllXml]
           FROM [dbo].[ELMAH_Error] ORDER BY [TimeUtc] desc", connection))
            {
                // Make sure the command object does not already have
                // a notification object associated with it.
                command.Notification = null;

                SqlDependency dependency = new SqlDependency(command);
                dependency.OnChange += new OnChangeEventHandler(ELMAHdependency_OnChange);

                if (connection.State == ConnectionState.Closed)
                    connection.Open();

                using (var reader = command.ExecuteReader())
                    return reader.Cast<IDataRecord>()
                        .Select(x => new ElmahException()
                        {
                            ErrorId = x.GetGuid(0),
                            Application = x.GetString(1),
                            Host = x.GetString(2),
                            Type = x.GetString(3),
                            Source = x.GetString(4),
                            Error = x.GetString(5),
                            User = x.GetString(6),
                            Code = x.GetInt32(7),
                            TimeStamp = x.GetDateTime(8).ToString().Replace("T", " ")
                        }).ToList();
            }

        }
    }

    private void ELMAHdependency_OnChange(object sender, SqlNotificationEventArgs e)
    {
        Console.Write("Exception table changed!");
    }

这很好用，所以随着我的风帆，我接下来就为日志信息做了类似的事情：

 public IEnumerable<LogMessage> GetLogMessages()
    {
        using (var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["elmah-sqlserver"].ConnectionString))
        {
            connection.Open();
            using (SqlCommand command = new SqlCommand(@"SELECT [application],[time_stamp],[logLevel],[logger],[message]
           FROM [dbo].[LogTable] ORDER BY [time_stamp] desc", connection))
            {
                // Make sure the command object does not already have
                // a notification object associated with it.
                command.Notification = null;

                SqlDependency dependency = new SqlDependency(command);
                dependency.OnChange += new OnChangeEventHandler(NLOGdependency_OnChange);

                if (connection.State == ConnectionState.Closed)
                    connection.Open();

                using (var reader = command.ExecuteReader())
                    return reader.Cast<IDataRecord>()
                        .Select(x => new LogMessage()
                        {
                            Application = x.GetString(0),
                            TimeStamp = x.GetDateTime(1).ToString().Replace("T", " "),
                            LogLevel = x.GetString(2),
                            Logger = x.GetString(3),
                            Message = x.GetString(4)
                        }).ToList();
            }

        }
    }

    private void NLOGdependency_OnChange(object sender, SqlNotificationEventArgs e)
    {
        Console.Write("Log table has changed!");
    }

此时，我只会在日志表发生变化时收到警报。通过混合中的这个额外SqlDependency，ELMAHdependency_OnChange永远不会被调用。如果我注释掉我的GetLogMessages()方法，则会再次调用ELMAHdependency_OnChange。

看起来多个SqlDependency个对象是互斥的。关于如何同时监控两个表的任何想法？

Answer 1

可以使用分号连接另一个SqlStatement。

以下是代码中的代码段，包含我的更改。

 [...]
 connection.Open();

 var queries = new [] {@"SELECT [application],[time_stamp],[logLevel],[logger],[message] FROM [dbo].[LogTable] ORDER BY [time_stamp] desc",
                       @"SELECT [ErrorId],[Application],[Host],[Type],[Source],[Message],[User],[StatusCode],[TimeUtc],[Sequence],[AllXml] FROM [dbo].[ELMAH_Error] ORDER BY [TimeUtc] desc"};

 using (SqlCommand command = new SqlCommand(string.Join("; ", queries), connection))
 {
 [...]

一旦调用该事件，重新注册SqlDependency也很重要。否则事件只会被触发一次..

    private void dependency_OnChange(object sender, SqlNotificationEventArgs e)
    {
        SqlDependency dependency = sender as SqlDependency;
        if (dependency != null) dependency.OnChange -= dependency_OnChange;

        if (e.Type == SqlNotificationType.Change)
        {
            // Do things
        }
        SetupDatabaseDependency();
    }

SetupDatabaseDependency()将包含设置SqlDependency。

的代码

Answer 2

使用从两个表而不是查询中选择的存储过程。

CREATE PROCEDURE [dbo].[SQLDependency_TestTable1_TestTable2]
    @MaxIdxTestTable1 INT = 1, @MaxIdxTestTable2 INT = 1
AS
-- Don't do this - SQLDependency doesn't like.
--SET TRANSACTION ISOLATION LEVEL READ COMMITTED

-- Don't do this either - SQLDependency doesn't like.
--SELECT MAX(ID) FROM ehmetrology.TestTable1 
--SELECT COUNT(ID) FROM ehmetrology.TestTable1

-- See here for a whole list of things SQLDependency doesn't like:
-- stackoverflow.com/questions/7588572/what-are-the-limitations-of-sqldependency/7588660#7588660

SELECT DCIdx FROM TestTable1 WHERE Idx >= @MaxIdxTestTable1 
ORDER BY DCIdx DESC;

SELECT DCIdx FROM TestTable2 WHERE Idx >= @MaxIdxTestTable2 
ORDER BY DCIdx DESC;

GO

然后在.NET端执行此操作（原谅VB）：

    Using adapter As New SqlDataAdapter(mSQLD_Command)
        adapter.Fill(mSQLD_DataSet, SQLD_DATASET_TABLENAME)
    End Using

    ' Reload the dataset that's bound to the grid.
    If mSQLD_DataSet.Tables.Count = 2 Then
        Dim iTest1Index As Integer = 0
        Dim iTest2Index As Integer = 0

        If Integer.TryParse(mSQLD_DataSet.Tables(0).Rows(0).Item(0).ToString, iTest1Index) Then
            If iTest1Index<> moTest1.MaxDCIdx Then
                GetTest1Data(True)
            End If
        End If

        If Integer.TryParse(mSQLD_DataSet.Tables(1).Rows(0).Item(0).ToString, iTest2Index) Then
            If iTest2Index <> moTest2.MaxDCIdx Then
                GetTest2Data()
            End If
        End If

    End If

通过使用存储过程，您没有像使用一致的select语句那样移动所有这些记录。每次修改2个表中的任何一个时，您都会收到通知，因此您必须深入了解结果以确定哪个表已更改。

无法使用SqlDependency监视多个表

2 个答案: