Question

嗨stackoverflow人！我最近开发了一个简单的vb.net程序，它连接到一个mysql数据库，用于注册和登录具有给定凭据的用户。我已经使用此代码注册我的用户，但我一直得到错误（在代码下面）

Dim insertUser As String = "INSERT INTO users(ID, username, password, email, verif)" _
        & " VALUES('','" & Username.Text & "','" & Password.Text & "','" & Email.Text & "','" & currentRandString & "');"
        Dim checkUsername As String = "SELECT * FROM users WHERE username='" & Username.Text & "'"
        MysqlConn = New MySqlConnection()
        MysqlConn.ConnectionString = mysqlconntxt4reg
        MysqlConn.Open()

        Dim myCommand As New MySqlCommand
        myCommand.Connection = MysqlConn
        myCommand.CommandText = checkUsername

        myAdapter.SelectCommand = myCommand
        Dim myData As MySqlDataReader
        myData = myCommand.ExecuteReader

        If myData.HasRows > 0 Then
            MsgBox("Username Already In Use...", MsgBoxStyle.Critical, "Error")
            myData.Close()
        Else
            myData.Close()
            Dim myCommand2 As New MySqlCommand
            myCommand2.Connection = MysqlConn
            myCommand2.CommandText = insertUser

            myAdapter.SelectCommand = myCommand2
            Dim myData2 As MySqlDataReader
            myData2 = myCommand2.ExecuteReader
            Mail(Email.Text, currentRandString)
            Me.Close()
            myData2.Close()
        End If
    Catch myerror As MySqlException
        MsgBox("Error While Connecting To Database:" & vbNewLine & vbNewLine & myerror.ToString, MsgBoxStyle.Critical, "Error")
    Finally
        MysqlConn.Dispose()
    End Try

在打开其他数据之前我已经关闭了所有的datareader，所以我不明白为什么这不起作用...

错误： enter image description here

Link to Error Image

感谢您对此话题的任何帮助！谢谢 Rodit

Answer 1

我会在所有一次性对象周围使用using语句，以确保它们在不再需要时释放每个对连接的引用，但是看看你的代码，我认为你根本不需要datareaders，因为您可以使用命令解决问题

Dim insertUser As String = "INSERT INTO users(username, password, email, verif)" _
                            & " VALUES(@p1, @p2,@p3,@p4)"
Dim checkUsername As String = "SELECT COUNT(*) FROM users WHERE username=@p1"

Using MysqlConn = New MySqlConnection(mysqlconntxt4reg)
Using myCommand = New MySqlCommand(checkUsername, MysqlConn)
    MysqlConn.Open()
    myCommand.Parameters.AddWithValue("@p1", Username.Text)
    Dim result = myCommand.ExecuteScalar()
    if result IsNot Nothing AndAlso Convert.ToInt32(result) > 0 Then
         MsgBox("Username Already In Use...", MsgBoxStyle.Critical, "Error")
    Else
        Using myCommand2 = New MySqlCommand(insertUser, MysqlConn)
               mycommand2.Parameters.AddWithValue("@p1",Username.Text)
               mycommand2.Parameters.AddWithValue("@p2",Password.Text )
               mycommand2.Parameters.AddWithValue("@p3",Email.Text) 
               mycommand2.Parameters.AddWithValue("@p4",currentRandString )
               myCommand2.ExecuteNonQuery()
               Mail(Email.Text, currentRandString)
        End Using      
    End If
End Using
End Using

当然我已经用参数化查询替换了你的字符串连接。这是避免Sql Injection

的重要事项

我已经用可以与命令ExecuteScalar一起使用的标量操作替换了检查用户存在的查询。此外，在第一个查询中，您似乎尝试插入带有空字符串的字段ID。我认为第一个字段（ID）是一个自动编号字段，在这种情况下，您不会将其添加到插入查询中，也不会传递任何值，因为数据库将为您计算该字段。

为什么我一直收到这个mysql错误？

1 个答案: