[MySQL VB.Net]如果字段为空，如何显示消息框 [英] [MySQL VB.Net] How to Show messagebox if a fields is blank

问题描述

大家好，我这里的代码有问题。如果用户错过了文本框字段空白，我想显示消息框。



这是我的代码：

 私有  Sub  btnSave_Click（发件人作为系统。对象，e  As  System.EventArgs）句柄 btnSave.Click 
 MySqlConn = 新 MySqlConnection 
 MySqlConn.ConnectionString = 
   server = localhost; userid = root; password = ianp; database = database 
  Dim  READER  As  MySqlDataReader 
 
 
 
 尝试 
 MySqlConn。 Open（）
  Dim 查询 As   String  
 Query =   insert into database.appointment（AppointmentID，FirstName，MiddleName，LastName，Date ，时间）值（'& txtAppointmentID.Text&  '，'& txtFNAppointment.Text&  '，'& txtMNAppointment.Text&  '，'& txtLNAppointment.Text&  '，'& dtDate.Text&  '，'& dtTime.Text&  '） 
 COMMAND = 新 MySqlCommand（Query，MySqlConn）
 READER = COMMAND.ExecuteReader 
 
 如果 txtFNAppointment.Text& txtMNAppointment.Text& txtLNAppointment.Text =   然后 
 MessageBox.Show（ 请填写所有必填字段！）
 
  Else  
 MessageBox.Show（ 成功保存记录）
 autogenerate_id（）
 结束 如果 
 
 MySqlConn.Close（）
 
  Catch  ex  As  MySqlException 
 MessageBox.Show（ex.Message）
 最后 
 MySqlConn.Dispose（）
 
 结束 尝试 

我有问题：当我把一个字段留空时。它显示MessageBox请填写所有必填字段！但它保存在mysql数据库中。我希望它能够中止保存，直到所有字段都填满为止。任何帮助将不胜感激。谢谢

解决方案

最好分别检查每个字段。你也需要退出子。因此，而不是

 如果 txtFNAppointment.Text& txtMNAppointment.Text& txtLNAppointment.Text =   然后 
 MessageBox.Show（ 请填写所有必填字段！）

尝试

 如果 txtFNAppointment.Text =   或 txtMNAppointment.Text =   或 txtLNAppointment.Text =   然后 
 MessageBox.Show（< span class =code-string> 请填写所有必填字段！）
 返回 
 结束 如果 

查询的内容，永远不会将值直接连接到SQL语句中。这使您可以打开SQL注入。相反，使用 SqlParameter [ ^ ]。有关更多讨论，请参阅正确执行数据库操作，版本3，参数 [< a href =http://www.codeproject.com/Articles/1020224/Properly-executing-database-operations#_version3target =_ blanktitle =New Window> ^ ]

验证并显示消息，如果缺少任何字段，否则执行插入

 如果 字符串 .IsNullOrWhiteSpace（txtFNAppointment.Text）或 字符串 .IsNullOrWhiteSpace（txtMNAppointment.Text）或  String  .IsNullOrWhiteSpace（txtLNAppointment.Text）然后 
 MessageBox.Show（ 请填写所有必填字段！ ）
  Else  
 COMMAND = 新 MySqlCommand（Query，MySqlConn）
 COMMAND.ExcuteNonQuery（）
 结束 如果 

Hi guys, im having trouble with my code here. I want to show messagebox if the user missed a textbox field blank.

Here's my code:

Private Sub btnSave_Click(sender As System.Object, e As System.EventArgs) Handles btnSave.Click
        MySqlConn = New MySqlConnection
        MySqlConn.ConnectionString =
            "server=localhost;userid=root;password=ianp;database=database"
        Dim READER As MySqlDataReader

        

        Try
            MySqlConn.Open()
            Dim Query As String
            Query = "insert into database.appointment (AppointmentID, FirstName, MiddleName, LastName, Date, Time) values ('" & txtAppointmentID.Text & "','" & txtFNAppointment.Text & "', '" & txtMNAppointment.Text & "', '" & txtLNAppointment.Text & "', '" & dtDate.Text & "', '" & dtTime.Text & "')"
            COMMAND = New MySqlCommand(Query, MySqlConn)
            READER = COMMAND.ExecuteReader

            If txtFNAppointment.Text & txtMNAppointment.Text & txtLNAppointment.Text ="" Then
                MessageBox.Show("Please fill-up all the required fields !")

            Else
                MessageBox.Show("Successfully Saved Record")
autogenerate_id()
            End If

            MySqlConn.Close()

        Catch ex As MySqlException
            MessageBox.Show(ex.Message)
        Finally
            MySqlConn.Dispose()

        End Try

I have problems: When i left a field blank. It Shows the MessageBox "Please fill-up all the required fields !" but it saves in the mysql database. I want for it to abort the save until all the fields are filled-up. Any help will be appreciated. Thanks

解决方案

It's best to check each field separately. Also you need to exit the sub. So instead of

If txtFNAppointment.Text & txtMNAppointment.Text & txtLNAppointment.Text ="" Then
MessageBox.Show("Please fill-up all the required fields !")

try

If txtFNAppointment.Text = "" Or txtMNAppointment.Text = "" Or txtLNAppointment.Text ="" Then
   MessageBox.Show("Please fill-up all the required fields !")
   Return
End If

And what comes to your query, never concatenate values directly into the SQL statement. This leaves you open to SQL injections. Instead, use SqlParameter[^]. For more discussion, see Properly executing database operations, version 3, parameters[^]

validate and show message if any filed is missing, otherwise do the insert

If String.IsNullOrWhiteSpace(txtFNAppointment.Text) or String.IsNullOrWhiteSpace(txtMNAppointment.Text) or String.IsNullOrWhiteSpace(txtLNAppointment.Text) Then
  MessageBox.Show("Please fill-up all the required fields !")
Else
   COMMAND = New MySqlCommand(Query, MySqlConn)
   COMMAND.ExcuteNonQuery()
End If

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