VB.NET更新方法

大家好。我想就更新数据库中特定记录的代码寻求帮助。我的后端是Microsoft Access，前端是Visual Basic。它给我一个错误“没有为一个或多个必需参数提供值”。此外，我还收到一个关于“对象引用未设置为对象实例”的问题

这是我的密码。谢谢：）

---

accessConnection

是全局（连接对象）变量吗？您必须已在该过程上创建了该对象的另一个实例

还有一件事，

clientID

也可以参数化。然后加上这一行

accessCommand.Parameters.AddWithValue("@clientID", selectedClient)

更新1

Private Sub UpdateClient()

    Dim recordsAffected As Integer = 0
    Dim sqlUpdateClient As String = "UPDATE tblClient " & _
                                    "SET clientCompany = ?, " & _
                                    "   clientStreetAddress = ?, " & _
                                    "   clientCity = ?, " & _
                                    "   clientContactPerson = ?, " & _
                                    "   clientContactNumber = ?, " & _
                                    "   clientEmail = ?, " & _
                                    "   clientMobileNumber = ? " & _
                                    "WHERE clientID = ?"

    Using accessConnection As New OleDbConnection("connectionStringHere")
        Using accessCommand As New OleDbCommand()
            With accessCommand
                .Connection = accessConnection
                .CommandType = CommandType.Text
                .CommandText = sqlUpdateClient
                .Parameters.AddWithValue("clientCompany", txtClientCompany.Text)
                .Parameters.AddWithValue("clientStreetAddress", txtClientStreetAddress.Text)
                .Parameters.AddWithValue("clientCity", txtClientCity.Text)
                .Parameters.AddWithValue("clientContactPerson", txtClientContactPerson.Text)
                .Parameters.AddWithValue("clientContactNumber", txtClientPhoneNumber.Text)
                .Parameters.AddWithValue("clientEmail", txtClientEmailAddress.Text)
                .Parameters.AddWithValue("clientMobileNumber", txtClientMobileNumber.Text)
                .Parameters.AddWithValue("clientID", selectedClient)
            End With
            Try
                accessConnection.Open()
                recordsAffected = accessCommand.ExecuteNonQuery()
            Catch ex As OleDBException
                lblError.Text = ex.Message.ToString()
            Finally
                accessConnection.Close()
            End Try

            If recordsAffected = 0 Then
                MsgBox("Record updated failed!", MsgBoxStyle.Exclamation, "Project Analysis System")
            Else
                MsgBox("Record updated successfully!", MsgBoxStyle.Information, "Project Analysis System")
                PopulateClientList()
            End If
        End Using
    End Using

End Sub

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在哪里定义了

accessConnection

和

selectedClient

，表

tblClient

的定义是什么？您在哪里收到“对象引用未设置为对象实例”？另外，为什么不将selectedClient指定为参数@clientID？@vane:accessConnection包含我的连接字符串，而selectedClient来自listview，在listview中，当我从listview中选择一个项目时，它返回一个整数。@astander:当我试图创建一个参数“clientID”时，它给我的错误是“没有为一个或多个必需参数提供值“。有一次，当我尝试将SQL字符串与一个变量连接起来时，它起了作用，但在我的其他形式中，考虑到变量和名称的所有替换。我不相信Access支持命名参数，是吗？请在更新字符串中使用问号而不是命名参数，然后确保以正确的顺序将参数添加到accessCommand对象。@JohnWoo clientID不需要参数化；这是最佳实践，但在不将其作为参数并像他所做的那样连接它的情况下，它会起作用。当您提供参数和其他值时，有些值并没有，这很奇怪。无论如何，这是用户的选择。@JohnWoo我完全同意，并认为它也应该参数化，我只是不希望错误信息四处传播，因为你说它必须参数化，而这句话是错误的。@JohnWoo：是的，accessConnection是我的OleDbConnection。但我刚刚把这行代码放在了我的全局部分。我不知道是我自己，还是我的代码真的错了，但当我使用相同的序列、工具箱中的相同对象、相同的名称和相同的参数时，它起作用了，有时也不起作用。@Ju chan

Private Sub UpdateClient()

    Dim recordsAffected As Integer = 0
    Dim sqlUpdateClient As String = "UPDATE tblClient " & _
                                    "SET clientCompany = ?, " & _
                                    "   clientStreetAddress = ?, " & _
                                    "   clientCity = ?, " & _
                                    "   clientContactPerson = ?, " & _
                                    "   clientContactNumber = ?, " & _
                                    "   clientEmail = ?, " & _
                                    "   clientMobileNumber = ? " & _
                                    "WHERE clientID = ?"

    Using accessConnection As New OleDbConnection("connectionStringHere")
        Using accessCommand As New OleDbCommand()
            With accessCommand
                .Connection = accessConnection
                .CommandType = CommandType.Text
                .CommandText = sqlUpdateClient
                .Parameters.AddWithValue("clientCompany", txtClientCompany.Text)
                .Parameters.AddWithValue("clientStreetAddress", txtClientStreetAddress.Text)
                .Parameters.AddWithValue("clientCity", txtClientCity.Text)
                .Parameters.AddWithValue("clientContactPerson", txtClientContactPerson.Text)
                .Parameters.AddWithValue("clientContactNumber", txtClientPhoneNumber.Text)
                .Parameters.AddWithValue("clientEmail", txtClientEmailAddress.Text)
                .Parameters.AddWithValue("clientMobileNumber", txtClientMobileNumber.Text)
                .Parameters.AddWithValue("clientID", selectedClient)
            End With
            Try
                accessConnection.Open()
                recordsAffected = accessCommand.ExecuteNonQuery()
            Catch ex As OleDBException
                lblError.Text = ex.Message.ToString()
            Finally
                accessConnection.Close()
            End Try

            If recordsAffected = 0 Then
                MsgBox("Record updated failed!", MsgBoxStyle.Exclamation, "Project Analysis System")
            Else
                MsgBox("Record updated successfully!", MsgBoxStyle.Information, "Project Analysis System")
                PopulateClientList()
            End If
        End Using
    End Using

End Sub