关系表的SQL依赖关系 [英] SQL dependency on relational tables
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问题描述
我有两个相关的表(tbVehicles和tbVehiclesDoc)我正在运行下面的sql依赖项,但它很多时间和我的程序冻结。请协助。
我希望程序在其他用户修改它们时更新这些表。
我的代码
I have two related tables (tbVehicles and tbVehiclesDoc) I am running the below sql dependency but it is firring many time and my program freezes. please assist.
I want the program to update these tables when another user modifies them.
my Code
Public Sub getdata()
Try
If tbdataset.Tables.Contains("tbVehicles") Then
If tbdataset.Tables("tbVehiclesDoc") IsNot Nothing Then
For f As Integer = tbdataset.Tables("tbVehiclesDoc").ChildRelations.Count - 1 To 0 Step -1
tbdataset.Tables("tbVehiclesDoc").ChildRelations(f).ChildTable.Constraints.Remove(tbdataset.Tables("tbVehiclesDoc").ChildRelations(f).RelationName)
tbdataset.Tables("tbVehiclesDoc").ChildRelations.RemoveAt(f)
Next
tbdataset.Tables("tbVehiclesDoc").ChildRelations.Clear()
tbdataset.Tables("tbVehiclesDoc").ParentRelations.Clear()
tbdataset.Tables("tbVehiclesDoc").Constraints.Clear()
tbdataset.Tables.Remove("tbVehiclesDoc")
End If
tbdataset.Tables.Remove("tbVehicles")
tbdataset.EnforceConstraints = True
End If
gridVehicles.DataSource = Nothing
Catch ex As Exception
MsgBox(ex.ToString)
'' Exit Sub
End Try
command.Notification = Nothing
Dim dependency As New SqlDependency(command)
AddHandler dependency.OnChange, AddressOf dependency_OnChange
Dim adapter As New SqlDataAdapter(command)
adapter.Fill(tbdataset, "tbVehicles")
''----
End Sub
Private Sub toupdate()
If CanRequestNotifications() Then
If connection Is Nothing Then
connection = New SqlConnection(GetConnectionString())
connection.Open()
End If
If connection.State = ConnectionState.Closed Then
connection.Open()
End If
If command Is Nothing Then
command = New SqlCommand(GETSQL(), connection)
End If
End If
getdata()
End Sub
Private Function GETSQL() As String
Return "Select Rtrim(VehcID) as VehcID,RTrim(VehcModel), Rtrim(VehcRegNo) as VehcRegNo, Rtrim(VehcFourWheel), Rtrim(VehcCondition), Rtrim(VehcLastKM),Rtrim(VehcBranch), Rtrim(VehcDepartment), Rtrim(VehcDriver), Rtrim(VehcRemarks), VehcPic from dbo.tbVehicles"
End Function
Private Sub dependency_OnChange(ByVal sender As Object, ByVal e As SqlNotificationEventArgs)
'' This event will occur on a thread pool thread.
'' It is illegal to update the UI from a worker thread
'' The following code checks to see if it is safe
'' update the UI.
Dim i As ISynchronizeInvoke = CType(Me, ISynchronizeInvoke)
'' If InvokeRequired returns True, the code
'' is executing on a worker thread.
If i.InvokeRequired Then
'' Create a delegate to perform the thread switch
Dim tempDelegate As New OnChangeEventHandler( _
AddressOf dependency_OnChange)
Dim args() As Object = {sender, e}
'' Marshal the data from the worker thread
'' to the UI thread.
i.BeginInvoke(tempDelegate, args)
Return
End If
'' Remove the handler since it''s only good
'' for a single notification
Dim dependency As SqlDependency = _
CType(sender, SqlDependency)
RemoveHandler dependency.OnChange, _
AddressOf dependency_OnChange
'' Reload the dataset that''s bound to the grid.
getdata()
End Sub
推荐答案
您正在创建一个无限循环,在您使用的获取数据中事件依赖性更改然后更改数据,当您更改数据依赖性更改事件时触发并重新开始。
You are creating an infinite loop, in your get data you use the event dependancy change and then change the data, when you change the data dependancy change event fires and you start again.
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