如何解决Mysql 连接未通过 VB.NET 应用程序关闭
这是我第一次来这里，因为我遇到的这个问题，我快疯了：
我正在使用多种类型的连接（MysqL、odbc 和 sql 服务器）使用 VB.NET 开发 Windows 窗体应用程序，一切正常，直到我进入 MysqL。 MysqL 服务器是一台物理 Windows 7 pc，我通过 IPSEC VPN TUNNEL 连接到它。
我需要每 x 秒执行 2 个 MysqL 连接，如果我在第一个连接后得到某种类型的结果，那么我将打开第二个，每 x 秒以此类推（这些都写在我的 timer.tick 事件中处理程序）。 问题是 MysqL 服务器上的一些连接经常在 MysqL 服务器上保持活动状态（ESTABLISHED），我不知道为什么......代码看起来不错，在正确的时间声明了 open 和 close 方法，我'我也尝试过 dispose、ClearPool 和 ClearallPools 方法，但我一直保持这些连接，直到我关闭我的程序或达到连接限制。
代码如下：
类连接：
Public Sub connMysqL()
Dim connstring As String
Try
If stabilimento = "1PR" Then
If cesoia = "" Then
connstring = "server=192.168.123.18;userid=xx;password=xx;database=xx;Connect Timeout=30"
Else
connstring = "server=192.168.123.253;userid=xx;password=xx;database=xx;Connect Timeout=30"
End If
End If
If stabilimento = "2PR" Then
If cesoia = "" Then
connstring = "server=192.168.1.18;userid=xx;password=xx;database=xx;Connect Timeout=30"
Else
connstring = "server=192.168.123.253;userid=root;password=xx;database=xx;Connect Timeout=30"
End If
End If
conMysqL = New MysqLConnection(connstring)
If conMysqL.State = ConnectionState.Closed Then
conMysqL.open()
End If
Catch ex As Exception
MsgBox(ex.ToString)
End Try
End Sub
执行迭代的类：
Private Sub Timer1_Tick(sender As Object,e As EventArgs) Handles Timer1.Tick
connMysqL()
comm = New MysqLCommand("SELECT count_1,count_2,start_stop,data_ora,id FROM plc_contatori where plc_nome='" + plc_nome + "' and data_ora > '" + data_ieri.ToString("yyyy/MM/dd") + "' order by data_ora desc limit 1",conMysqL)
dr = comm.ExecuteReader()
While (dr.Read())
count_1(0) = dr.GetValue(0)
start_stop(0) = dr.GetValue(2)
data_ora(0) = dr.GetValue(3)
If id <> dr.GetValue(4) And count_2(0) <> dr.GetValue(1) Then
id = dr.GetValue(4)
count_2(0) = dr.GetValue(1)
Else
Exit Sub
End If
End While
dr.Close()
dr.dispose()
conMysqL.Close()
conMysqL.dispose()
conMysqL.ClearPool(conMysqL)
conMysqL.ClearallPools()
If Not conMysqL Is nothing Then conMysqL = nothing
comm.dispose()
If start_stop(0) = 1 Then
Exit Sub
End If
Dim dum_count_2 As Integer = count_2(0) - 1
connMysqL()
comm = New MysqLCommand("select count_1,data_ora from plc_contatori where plc_nome='" + plc_nome + "' and data_ora > '" + data_ieri.ToString("yyyy/MM/dd") + "' AND count_2=" + dum_count_2.ToString + " ORDER BY data_ora desc limit 1",conMysqL)
dr = comm.ExecuteReader()
While (dr.Read())
count_1(1) = dr.GetValue(0)
count_2(1) = dr.GetValue(1)
start_stop(1) = dr.GetValue(2)
data_ora(1) = dr.GetValue(3)
End While
dr.Close()
dr.dispose()
conMysqL.Close()
conMysqL.dispose()
conMysqL.ClearPool(conMysqL)
conMysqL.ClearallPools()
If Not conMysqL Is nothing Then conMysqL = nothing
comm.dispose()
If count_1(0) = count_1(1) And start_stop(1) <> 1 And count_2(0) <> count_2(1) Then
'sub that reads some values from an odbc connection
CheckFermo()
End If
End Sub
注意，我在这部分代码中没有声明的变量是在表单的公共类中声明的。
我想知道有什么问题...也许在第一个连接被服务器关闭之前建立了第二个连接？
解决方法
我将 connMySQL 方法更改为返回连接字符串的函数。我已经声明了几个变量，所以代码是有意义的。我对数据类型做了几个假设。如果这些值实际上存储为字符串，您可能需要将其改回 String 和 VarChar。 （我希望他们不是）
您可以使用单个连接，但所有分配和比较都将在打开连接时进行。
Private stabilimento As String
Private cesoia As String
Public Function connMySQL() As String
Dim connstring As String
Select Case True
Case stabilimento = "1PR" And cesoia = ""
connstring = "server=192.168.123.18;userid=xx;password=xx;database=xx;Connect Timeout=30"
Case stabilimento = "2PR" And cesoia = ""
connstring = "server=192.168.1.18;userid=xx;password=xx;database=xx;Connect Timeout=30"
Case Else
connstring = "server=192.168.123.253;userid=root;password=xx;database=xx;Connect Timeout=30"
End Select
Return connstring
End Function
Private count_1(10) As Integer
Private count_2(10) As Integer
Private start_stop(10) As Integer
Private data_ora(10) As Date
Private id As Integer
Private plc_nome As String
Private data_ieri As Date
Private Sub Timer1_Tick(sender As Object,e As EventArgs) Handles Timer1.Tick
Using dt As New DataTable
Using cn As New MySqlConnection(connMySQL),comm = New MySqlCommand("SELECT count_1,count_2,start_stop,data_ora,id
FROM plc_contatori
where plc_nome= @plcNome and data_ora > @dataOra
order by data_ora desc
limit 1",cn)
comm.Parameters.Add("plcNome",MySqlDbType.VarChar).Value = plc_nome
comm.Parameters.Add("dataOra",MySqlDbType.Date).Value = data_ieri '.ToString("yyyy/MM/dd")
cn.Open()
Using dr = comm.ExecuteReader
dt.Load(dr)
End Using 'closes and disposes reader
End Using 'closes and dispose connection and command
count_1(0) = CInt(dt(0)(0))
start_stop(0) = CInt(dt(0)(2))
data_ora(0) = CDate(dt(0)(3))
If id <> CInt(dt(0)(4)) AndAlso count_2(0) <> CInt(dt(0)(1)) Then
id = CInt(dt(0)(4))
count_2(0) = CInt(dt(0)(1))
Else
Exit Sub
End If
End Using 'disposes DataTable
If start_stop(0) = 1 Then
Exit Sub
End If
Dim dum_count_2 As Integer = count_2(0) - 1
Using dt As New DataTable
Using cn As New MySqlConnection(connMySQL),comm As New MySqlCommand("select count_1,data_ora
from plc_contatori
where plc_nome= @plcNome
and data_ora > @dataOra
AND count_2= @count2
ORDER BY data_ora desc
limit 1",cn)
comm.Parameters.Add("@plcNome",MySqlDbType.VarChar).Value = plc_nome
comm.Parameters.Add("@dataOra",MySqlDbType.Date).Value = data_ieri '.ToString("yyyy/MM/dd")
comm.Parameters.Add("@count2",MySqlDbType.Int32).Value = dum_count_2 '.ToString
cn.Open()
Using dr = comm.ExecuteReader()
dt.Load(dr)
End Using
End Using
count_1(1) = CInt(dt(0)(0))
count_2(1) = CInt(dt(0)(1))
start_stop(1) = CInt(dt(0)(2))
data_ora(1) = CDate(dt(0)(3))
End Using
If count_1(0) = count_1(1) AndAlso start_stop(1) <> 1 AndAlso count_2(0) <> count_2(1) Then
'sub that reads some values from an odbc connection
CheckFermo()
End If
End Sub
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