Question

我的Windows窗体中有两个列表框，其中第一个包含一堆ID，当选择ID时，MySQL数据库中的所有属性都使用第二个列表框显示。

我的代码：

Private Sub lstUsersKey_SelectedIndexChanged(sender As Object, e As EventArgs) Handles lstUsersKey.SelectedIndexChanged
    If (lstUsersKey.SelectedIndex.ToString IsNot Nothing) Then
        Dim UserID As Integer = CInt(lstUsersKey.SelectedItem.ToString)

        lstUsersValue.Items.Clear()

        lstUsersValue.Items.Add("User ID: " & UserID)
        lstUsersValue.Items.Add("Forename: " & frmLogin.User.GetForename)
        lstUsersValue.Items.Add("Surname: " & frmLogin.User.GetSurname)
        lstUsersValue.Items.Add("Admin: " & frmLogin.User.IsAdmin)
        lstUsersValue.Items.Add("Username: " & frmLogin.User.GetUsername)
        lstUsersValue.Items.Add("Password: -") '& frmLogin.User.GetPassword
        lstUsersValue.Items.Add("Phone Number: " & frmLogin.User.GetPhoneNumber)
        lstUsersValue.Items.Add("Address: " & frmLogin.User.GetAddress())
        lstUsersValue.Items.Add("Postcode: " & frmLogin.User.GetPostcode())
        lstUsersValue.Items.Add("Email Address: " & frmLogin.User.GetUserEmailAddress)
    End If
End Sub

我的User类中的函数看起来像这样但具有不同的参数：

Function GetPostcode()
    Return frmLogin.MySQL.SelectQuery("Postcode", "tbluser", "Username", "@username", Me.Username)
End Function

我的MySQL类包含此功能：

Function SelectQuery(ByVal ColumnName As String, ByVal tblName As String, ByVal ConditionColumn As String, ByVal ConditionCheckOperator As String, ByVal ConditionCheckValue As String)
    Dim Query As String = "SELECT " & ColumnName & " " & "FROM " & tblName & " " & "WHERE " & ConditionColumn & "=" & ConditionCheckOperator
    Dim Connection As New MySqlConnection(frmLogin.MySQL.ConnectionDetails)
    Dim Command = New MySqlCommand(Query, Connection)
    Connection.Open()
    Dim Result As Object
    Command.Parameters.AddWithValue(ConditionCheckOperator, ConditionCheckValue)
    Result = Command.ExecuteScalar
    Command.Dispose()
    Connection.Close()
    If Result IsNot Nothing Then
        Return Result.ToString
    Else
        Return ""
    End If
End Function

问题是没有从我的数据库加载数据，我不知道如何修复它以及是否有更简单的方法来运行大量查询而无需每次我想运行时都建立新的连接查询。

Answer 1

所以我通过改变SelectQuery Function的工作方式解决了这个问题。我找到了一种在stackoverflow上运行查询的有效方法，所以我复制了代码并对其进行了调整。

Function SelectQuery(ByVal ColumnName As String, ByVal tblName As String, ByVal ConditionColumn As String, ByVal Operator1 As String, ByVal Value1 As Object)
        Dim Query As String = "SELECT " & ColumnName & " " & "FROM " & tblName & " " & "WHERE " & ConditionColumn & "=" & Operator1
        Dim Result As String = ""

        Using Conn As New MySqlConnection(ConnectionDetails)
            Using Comm As New MySqlCommand()
                With Comm
                    .Connection = Conn
                    .CommandText = Query
                    .CommandType = CommandType.Text
                    .Parameters.AddWithValue(Operator1, Value1)
                End With
                Try
                    Conn.Open()
                    Dim Reader As MySqlDataReader = Comm.ExecuteReader
                    While Reader.Read() OrElse (Reader.NextResult And Reader.Read)
                        Result += Reader.GetString(0)
                    End While
                Catch ex As Exception
                    Return "Error"
                    MsgBox("select error: " & ex.ToString)
                End Try
            End Using
        End Using

        Return Result

    End Function

vb.net快速运行MySQL查询

1 个答案: