Question

我正在用Access数据库做VB，我想创建一个按钮。哪个保存按钮检查尝试插入的数据在哪里重复或不与我的数据库进行比较。

这是我的代码，问题是我输入的内容只是显示用户已经存在。

 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
  MyConn = New OleDbConnection
  MyConn.ConnectionString = connString

  MyConn.Open()
  If (ComboBox2.Text = "") And (ComboBox3.Text = "") 
      And (TextBox3.Text = "") And (ComboBox4.Text = "") 
  Then
   MsgBox("Please fill-up all fields!")
  Else
   Dim theQuery As String = ("SELECT * FROM Table1 
      WHERE"" [Subject_Code]=@Subject_Code ,[Day]=@Day, 
              [Times]=@Times , [Lecture]=@Lecture and [Class_Room]=@Class_Room""")

   Dim cmd1 As OleDbCommand = New OleDbCommand(theQuery, MyConn)
   cmd1.Parameters.AddWithValue("@Subject_Code", TextBox6.Text)
   cmd1.Parameters.AddWithValue("@Day", ComboBox2.Text)
   cmd1.Parameters.AddWithValue("@Times", ComboBox3.Text)
   cmd1.Parameters.AddWithValue("@Lecture", TextBox3.Text)
   cmd1.Parameters.AddWithValue("@Class_Room", ComboBox4.Text)

   Using reader As OleDbDataReader = cmd1.ExecuteReader()
    If reader.HasRows Then
     'User already exists
     MsgBox("User Already Exist!")
   Else
    Dim Update As String = "INSERT INTO [Table1] 
     ([Subject_Code], [Subject],
      [Day], [Times], [Level],[Semester], [Lecture],[Class], [Class_Room])
     VALUES (?,?,?,?,?,?,?,?,?)"

     Using cmd = New OleDbCommand(Update, MyConn)
      cmd.Parameters.AddWithValue("@p1", TextBox6.Text)
      cmd.Parameters.AddWithValue("@p2", TextBox1.Text)
      cmd.Parameters.AddWithValue("@p3", ComboBox2.Text)
      cmd.Parameters.AddWithValue("@p4", ComboBox3.Text)
      cmd.Parameters.AddWithValue("@p5", ComboBox1.Text)
      cmd.Parameters.AddWithValue("@p6", ComboBox6.Text)
      cmd.Parameters.AddWithValue("@p7", TextBox3.Text)
      cmd.Parameters.AddWithValue("@p8", ComboBox5.Text)
      cmd.Parameters.AddWithValue("@p9", ComboBox4.Text)
      MsgBox("New Data Is Saved")
      cmd.ExecuteNonQuery()
     End Using
   End If
  End Using
 End If

Answer 1

首先快速浏览一下你的theQuery变量，它可能只是在你输入SO的地方出错了，但如果没有尝试：

  Dim theQuery As String = "SELECT * FROM Table1 " & 
                           "WHERE [Subject_Code] = @Subject_Code " & 
                           "AND [Day] = @Day " & 
                           "AND [Times] = @Times " & 
                           "AND [Lecture] = @Lecture " & 
                           "AND [Class_Room] = @Class_Room"

您对现有用户的检查基于5个字段，新数据的插入有9个字段。在不知道业务案例的情况下，我无法确定这是否正确，或者缺少的4个字段对检查是否真正重要并导致返回意外行。

我个人接下来的步骤是：

在AddWithValue语句上放置一个断点并检查值是你所期待的
使用SSMS / Access中的值或等效值运行查询，并检查返回的行是否符合预期

如何确定VB.net中是否已存在记录？

1 个答案: