Question

我一直得到＃34;连接没有建立＆＃34;错误。虽然我想，通过打开与sqlLink.Open和sqlCheck.connection = sqlLink的连接会发生什么，但这个错误不会出现。

Imports System.Data.OleDb
Public Class StockAdd
    Dim path = System.Windows.Forms.Application.StartupPath
    Dim sqlLink As OleDbConnection
    Private Sub StockAdd_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        sqlLink = New OleDbConnection
        sqlLink.ConnectionString = ("Provider=Microsoft.ACE.OLEDB.12.0;Data Source='C:\Users\will\Documents\Computing\ComputingProjectDatabase.accdb';")

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim sqlCheck As New OleDbCommand
        Dim oleRdr As OleDbDataReader
        sqlLink.Open()
        Try
            Using sqlOrder As New OleDbCommand

                sqlCheck.Connection = sqlLink
                sqlCheck.CommandText = "SELECT count(*) FROM StockSystem WHERE [Stock ID] = @stockID"
                sqlCheck.Parameters.AddWithValue("@stockID", TextBox5.Text)

                oleRdr = sqlCheck.ExecuteReader()
                If oleRdr.HasRows = True Then
                    oleRdr.Read()
                    If oleRdr.Item(0) = 0 Then
                        sqlOrder.CommandText = "INSERT INTO StockSystem ([Stock ID], [Stock Price], [Stock Size], [Stock Quantity], [Stock Category]) VALUES ('" & TextBox5.Text & "','" & TextBox7.Text & "','" & TextBox6.Text & "','" & TextBox8.Text & "','" & TextBox9.Text & "')"
                        sqlOrder.ExecuteNonQuery()
                        MsgBox("Stock Details Stored.")
                    Else
                        MsgBox("Please check you have entered the correct data.")
                    End If
                End If
            End Using
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
        sqlLink.Close()
        Me.Close()
        Stock.Show()

    End Sub
End class

Answer 1

如果我的眼睛不让我失望，你就不要为sqlOrder命令设置连接。所以它无法执行你的sql文本。

请注意，您不能使用sqlLink连接，因为它由datareader使用。您需要一个新的连接对象（当然具有相同的连接字符串）

作为旁注，您的代码非常容易受到Sql Injection的攻击。如果一个或多个TextBox包含单引号char，则可能会出现严重问题。

始终使用参数化查询作为

之前用于COUNT（）语句的查询

数据库应用程序连接错误

1 个答案: