如何在VB.net上从数据库获取数据到文本框

Question

嗨我是Visual Basic的新手。我有一个按钮，当它点击时，它将通过用户输入的ID找到学生，并将数据输出到文本字段。我不确定我是否正确行事。因为我收到了这个错误[图片] >> http://img812.imageshack.us/img812/7650/gq0z.png

顺便说一句，这是我的代码到目前为止。有谁可以帮助我吗？谢谢！

        cmd.CommandText = "Select * from Student where Student_id = '" & id.Text & "'"
        cmd.Connection = db

        dr = cmd.ExecuteReader

        Try
            dr.Read()
            id.Text = dr.GetValue(0)
            Lname.Text = dr.GetValue(1)
            Fname.Text = dr.GetValue(2)
            Mname.Text = dr.GetValue(3)
            datet.Text = dr.GetValue(4)
            age.Text = dr.GetValue(5)
            male.Text = dr.GetValue(6)
            female.Text = dr.GetValue(7)
            status.Text = dr.GetValue(8)
            staddress.Text = dr.GetValue(9)
            cityAdd.Text = dr.GetValue(10)
            dr.Close()

        Catch ex As Exception
            MsgBox("" + ex.Message)
            dr.Close()
        End Try

Answer 1

cmd.CommandText = "Select * from Student where Student_id = '" & id.Text & "'"

改成：

if IsNumeric(id.text) Then
cmd.CommandText = "Select * from student where Student_id=@p1"
cmd.Prepare
cmd.Parameters.AddWithValue("@p1", id.text)
dr = cmd.ExecuteReader
....
Else
Exit Sub
End If

你可以这样做，或者

 dr = cmd.ExecuteReader

    Try
       with dr
        .Read()
        id.Text = .GetValue(0)
        end with
        dr.Close()

要么

with dr
    .read
    id.text = .item("id")
    .close

更容易阅读....

Answer 2

首先添加一个引用，如果你使用MySQL数据库就把它打赌。班级

Dim Connection As MySqlConnection
Dim command As MySqlCommand

把它放到你的文本框中

Connection = New MySqlConnection
Connection.ConnectionString = "Server=localhost;port=3306;userid=root;password=root;database=databasename"
Dim reader As MySqlDataReader

根是默认的

Try
  Connection.Open()
  Dim query As String
  query= "Select * from Databasename.tablename where fieldname='" & textbox1.text & "'"
  Command = New MySqlCommand(query, Connection)
  reader = Command.ExecuteReader
  While reader.Read
    Dim sname As String
    sname = reader.GetString("Fieldname")
    textbox1.Items.Add(sname)
  End While
  Connection.Close()
Catch e MySqlException
  MsgBox (ex.Message)
Finally
  Connection.Dispose
End Try

Answer 3

如果您使用的是Mysql Database，请先添加引用。添加MySql数据库的引用

1. 转到解决方案资源管理器并右键单击项目名称
2. 找到add-> references 将打开一个窗口
3. 在该窗口中，在Assemblies下选择框架。
4. 在右侧将有一个列表查找并选择Microsoft.VisualBasic.Compatability.Data
5. 在扩展中，查找并添加MySql.Data和MSDATASRC
6. 单击确定