此代码有问题 [英] problem with this code

问题描述

我已经使用此代码验证了不允许重复值的商品，但是我对此有疑问

i have validate an item which does not allow duplicate value by using this code but i have problem on it

If SQLstr <> Nothing Then
               MessageBox.Show("name is already used ")

           End If

这是我的源代码:

this is my source code:

Try
           Dim curdate As String
           Dim recstatus As String



           curdate = Now.Date
           recstatus = "A"

           If txtuser.Text = "" Then
               MessageBox.Show("Blank Record is NOT accepted")
               Exit Sub
           End If

           If txtpass.Text = "" Then
               MessageBox.Show("Blank Record is NOT accepted")
               Exit Sub
           End If
           If txtcpass.Text = "" Then
               MessageBox.Show("Blank Record is NOT accepted")
               Exit Sub
           End If

           If txtpass.Text.Trim <> txtcpass.Text.Trim Then
               MessageBox.Show("Both Password and Confirm Password Not Match")
               Exit Sub
           End If

           If (Comlevel.SelectedIndex = -1) Or Comlevel.Text = "" Then
               MessageBox.Show("Please select Level")
               Exit Sub
           End If



           Mycn = New SqlConnection("Data Source=IMAN-PC;Initial Catalog=control car;Integrated Security=True")
           Mycn.Open()
           SQLstr = "insert into login values('" & recstatus & "','" & txtuser.Text & "','" & txtpass.Text & "','" & Comlevel.Text & "','" & usrID & "','" & curdate & "','" & usrID & "', '" & curdate & "')"
           command = New SqlCommand(SQLstr, Mycn)
           icount = command.ExecuteNonQuery

           If SQLstr <> Nothing Then
               MessageBox.Show("name is here")

           End If

           If icount = 1 Then
               MessageBox.Show("Record Added Successfully", "Add Record", MessageBoxButtons.OK, MessageBoxIcon.Information)
           Else
               MessageBox.Show("No Record Inserted", "Add Record", MessageBoxButtons.OK, MessageBoxIcon.Information)

           End If




           Mycn.Close()

       Catch ex As Exception


           MessageBox.Show(ex.Message & "Could Not Insert Record")
           'Mycn.Close()

推荐答案

您可以使用SQL子句EXIST避免插入重复的行，例如，参见FAQ ^ ]

You may use the SQL clause EXIST to avoid inserting duplicate rows, see, for instance, the first question in the FAQ here[^].

您必须检查数据库中是否已存在用户ID.请参考以下代码:

You Have to Check that the User ID is Already Exist Or Not in DataBase.Refer the following Code :

Dim _Result As Object
Dim _ObjCmd As System.Data.SqlClient.SqlCommand = New System.Data.SqlClient.SqlCommand
       _ObjCmd.CommandText = "Select * From Login Where UserID ='" & txtUser.Text & "'"
       _ObjCmd.Connection = _SQLConnection
       Try
           _SQLConnection.Open()
           _Result = _ObjCmd.ExecuteReader
           _SQLConnection.Close()
       Catch ex As Exception

       End Try
       If _Result Is DBNull.Value Then
           'Your Insert Code
       Else
           MessageBox.Show("User Id Already Exist.")
       End If

希望对您有帮助.:)

I hope it will help you.:)

您的变量SQLstr永远不会等于零，因为在此之前将变量设置为插入SQL的三行.所以你的if语句...

Your variable SQLstr is never going to equal nothing because you set the variable to your insert SQL three lines before that. So your if statement...

If SQLstr <> Nothing Then
    MessageBox.Show("name is here")
End If

总是会被点击，因为SQLstr总是将您在其中设置的文本放在三行之前.

检查数据库中是否已经有一个值不是正确的值.我同意Manoj K Bhoir和CPallini的观点，您需要分别进行检查或通过其他方式进行检查.

will ALWAYS be hit because SQLstr will ALWAYS have the text you set in it three lines before.

It''s not the correct value to check to see if you already have a value in your database. I agree with Manoj K Bhoir and CPallini that you need to perform the check separately and by other means.

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