mysqlexception 未处理 - 已经有一个打开的 DataReader 与此 Connection 关联，必须先关闭

Question

所以我正在尝试使用表单来更新我在 xampp 上的数据库。但是当我尝试更新时，我在这部分的标题中出现错误：reader = objcommand.ExecuteReader() 非常感谢所有帮助。

代码如下：

    Imports MySql.Data
Imports MySql.Data.MySqlClient
Imports System.Drawing.Printing
Imports System
Imports System.Windows.Forms

Public Class frmClientDetails
    Dim form_type As Form
    Dim user_table As String
    Dim objconnection As New MySqlConnection("Server=localhost;database=ba-solutions;user id=root;password=")
    Dim sqlstring As String

    Private Sub frmClientDetails_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        DGVClient.Columns.Clear()
        Dim dt As New DataTable
        objdataadapter.SelectCommand = New MySqlCommand()
        objdataadapter.SelectCommand.Connection = objconnection
        objdataadapter.SelectCommand.CommandType = CommandType.Text
        objdataadapter.SelectCommand.CommandText = "SELECT * FROM Client_Details"
        objdataadapter.Fill(dt)


        rowposition = 0

        DGVClient.DataSource = dt

    End Sub
    Private Sub btnBack_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnBack.Click
        frmMainMenu.Show()
        Me.Hide()
    End Sub

    Private Sub btnClearAll_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClearAll.Click
        txtCompanyName.Clear()
        cbxCompanyType.Items.Clear()
        txtVAT.Clear()
        txtPAYE.Clear()
        txtAddressLine.Clear()
        txtCity.Clear()
        txtPostcode.Clear()
        txtEmail.Clear()
        txtPhoneNumber.Clear()
    End Sub


    Private Sub btnSubmit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSubmit.Click


        If Len(txtCompanyName.Text) < 1 Then
            MsgBox("Enter a Company Name")
            Return
        End If

        If Len(cbxCompanyType.Text) < 1 Then
            MsgBox("Enter a Company Type")
            Return
        End If

        If Len(txtVAT.Text) <> 9 Then
            MsgBox("The VAT Registration Number must be 9 numbers")
            Return
        End If

        If Len(txtPAYE.Text) <> 8 Then
            MsgBox("The PAYE and Tax Reference must be 8 characters")
            Return
        End If

        If Len(txtAddressLine.Text) < 1 Then
            MsgBox("Enter a First Line of Address")
            Return
        End If

        If Len(txtCity.Text) < 1 Then
            MsgBox("Enter a City Name")
            Return
        End If

        If Len(txtPostcode.Text) < 1 Then
            MsgBox("Enter a Postcode")
            Return
        End If

        If Len(txtEmail.Text) < 1 Then
            MsgBox("Enter an Email Address")
            Return
        End If

        If Len(txtPhoneNumber.Text) <> 11 Then
            MsgBox("The Phone Number must be 11 numbers ")
            Return
        End If

        Try
            objconnection.Open()
        Catch ex As Exception
            MsgBox("Error connecting to database", MsgBoxStyle.Information, "Connection Failed")
        End Try

        sqlstring = "Select * FROM client_details"
        Dim currentrecord As Integer = DGVClient.CurrentCellAddress.Y


        objconnection.Close()
        objconnection.Open()

        sqlstring = "Insert into `Client_Details` (`CompanyName` , `CompanyType` , `VATRegistrationNumber , `PAYEandTaxReference` , `AddressLine1` , `City` , `Postcode` , `Email` , `PhoneNumber') Values ('" &
 txtCompanyName.Text & "','" & cbxCompanyType.Text & "' , '" & txtVAT.Text & "','" & txtPAYE.Text & "' , '" & txtAddressLine.Text & "' , '" & txtCity.Text & "' , '" & txtPostcode.Text & "' , '" &
 txtEmail.Text & "' , '" & txtPhoneNumber.Text & "')"
        MsgBox("updated")
        objcommand.CommandText = sqlstring

        reader = objcommand.ExecuteReader()
        MsgBox("update")

    End Sub

    Public Sub count_records()
        Dim reccount As Integer
        reccount = DGVClient.Rows.Count = 1

    End Sub

End Class

所以基本上我正在填写表单上的文本框，一旦我点击提交，它应该使用新记录更新数据库。

Answer 1

切换到使用Parameterized Queries。这会帮助你。参数的数量将按顺序与表中的列数匹配。根据需要创建 ADO 对象并在 Sub 例程结束时关闭它们。

Insert Into [table name] Values(n1, n2, etc...)

SQL Tutorial