Mysql 列'；名字'；VB.Net错误不能为空

我正在创建一个系统。现在在我创建的登记表中卡住了。我使用Visual Studio 2008，并使用VB作为编程语言，使用MySql连接器5.1.1将其连接到MySql数据库

我有这些，它不是空的，但当我在我的注册表中输入数据时，我得到了这个

当我在数据库的表结构中将其更改为Null时，我在创建的注册表中输入的数据在数据库中变为Null

我不知道我的代码或数据库中是否有错误。我只是一个初学者，希望有人能帮助我

这是我按钮中的代码，用于在我的注册表中注册新用户帐户

    Private Sub btnCreate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCreate.Click
    Dim fname As String = txtboxfname.Text
    Dim lname As String = txtboxlname.Text
    Dim uname As String = txtboxuname.Text
    Dim pass As String = txtboxpass.Text
    Dim cpass As String = txtboxcpass.Text

    If txtboxfname.Text() = "" Or txtboxlname.Text() = "" Or txtboxuname.Text() = "" Or txtboxpass.Text() = "" Then

        MessageBox.Show("One Or More Fields Are Empty", "Missing Data", MessageBoxButtons.OK, MessageBoxIcon.Stop)

    ElseIf Not String.Equals(pass, cpass) Then

        MessageBox.Show("Wrong Confirmation Password", "Password Error", MessageBoxButtons.OK, MessageBoxIcon.Error)

    ElseIf unameExist(uname) Then

        MessageBox.Show("This Username Already Exists, Choose Another One", "Duplicate Username", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)

    Else

        Dim conn As New DBCon()
        Dim command As New MySqlCommand("INSERT INTO `login`(`first_name`, `last_name`, `username`, `password`) VALUES (@fn, @ln, @usn, @pwd)", conn.getConnection())

        command.Parameters.Add("@fn", MySqlDbType.VarChar).Value = fname
        command.Parameters.Add("@ln", MySqlDbType.VarChar).Value = lname
        command.Parameters.Add("@usn", MySqlDbType.VarChar).Value = uname
        command.Parameters.Add("@pwd", MySqlDbType.VarChar).Value = pass

        conn.openConnection()

        If command.ExecuteNonQuery() = 1 Then

            MessageBox.Show("Registration Completed Successfully", "User Added", MessageBoxButtons.OK, MessageBoxIcon.Information)
            conn.closeConnection()

        Else

            MessageBox.Show("Something Happened", "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error)
            conn.closeConnection()

        End If
    End If
End Sub

这是我把VB连接到MySql的代码

Imports MySql.Data.MySqlClient

Public Class DBCon
Private conn As New 
MySqlConnection("datasource=localhost;port=3306;username=root;password=;database=blood_elements")  

ReadOnly Property getConnection() As MySqlConnection
    Get
        Return conn
    End Get
End Property

Sub openConnection()

    If conn.State = ConnectionState.Closed Then
        conn.Open()
    End If

End Sub

Sub closeConnection()

    If conn.State = ConnectionState.Open Then
        conn.Close()
    End If

End Sub
End Class

---

你的系统有一个大问题。连接和其他一些数据库对象不仅需要关闭，还需要释放。它们使用非托管代码，当您调用.Dispose时，它们会释放该非托管代码中的资源。在使用连接的方法中创建连接。将数据访问代码与用户界面代码分开。毕竟，明天管理层可能会决定他们想要一个web应用程序。您可以将数据访问代码添加到不同的用户界面

幸运的是，vb.Net和C#提供了使用块关闭和处理对象的功能

事件子类中应该只有很少的代码。所有消息框都显示在用户界面代码中，而不是数据访问代码中

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    If Not ValidateNewUserInput() Then
        Exit Sub
    End If
    Dim Success = DataAccess.InsertUser(txtboxfname.Text, txtboxlname.Text, txtboxuname.Text, txtboxpass.Text)
    If Success Then
        MessageBox.Show("Registration Completed Successfully", "User Added", MessageBoxButtons.OK, MessageBoxIcon.Information)
    Else
        MessageBox.Show("Something Happened", "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error)
    End If
End Sub

在验证代码中，我对修剪过的字符串使用了IsNullOrEmpty。这应该覆盖空白，如选项卡或文本框中的空格。我还使用了OrElse，它是一种短路操作员。If语句将在找到True后立即停止计算条件

因为UserNameExists是一个共享方法，所以不需要创建DataAccess类的实例

Private Function ValidateNewUserInput() As Boolean
    If String.IsNullOrEmpty(txtboxfname.Text.Trim) OrElse String.IsNullOrEmpty(txtboxlname.Text.Trim OrElse String.IsNullOrEmpty(txtboxuname.Text.Trim OrElse String.IsNullOrEmpty(txtboxpass.Text.Trim) Then
            MessageBox.Show("One Or More Fields Are Empty", "Missing Data", MessageBoxButtons.OK, MessageBoxIcon.Stop)
        Return False
    ElseIf txtboxpass.Text <> txtboxcpass Then
        MessageBox.Show("Wrong Confirmation Password", "Password Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        Return False
    ElseIf DataAccess.UserNameExists(txtboxuname.Text) Then
        MessageBox.Show("This Username Already Exists, Choose Another One", "Duplicate Username", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
        Return False
    End If
    Return True
End Function

---

我看不到errro fname似乎为空或NULL，请检查它！我使用了你的代码，但仍然存在相同的问题。表的结构不是空的，当我在注册表中输入数据时，仍然会出现错误。我还将数据库中的表结构更改为Null，但当我在注册表中输入数据时，数据库中的数据仍然为Null。

Public Class DataAccess

    Private Shared ConStr As String = "datasource=localhost;port=3306;username=root;password=;database=blood_elements"

    Public Shared Function InsertUser(FirstName As String, LastName As String, UserName As String, PWord As String) As Boolean
        Using conn As New MySqlConnection(ConStr),
                command As New MySqlCommand("INSERT INTO `login`(`first_name`, `last_name`, `username`, `password`) VALUES (@fn, @ln, @usn, @pwd)", conn)
            command.Parameters.Add("@fn", MySqlDbType.VarChar).Value = FirstName
            command.Parameters.Add("@ln", MySqlDbType.VarChar).Value = LastName
            command.Parameters.Add("@usn", MySqlDbType.VarChar).Value = UserName
            command.Parameters.Add("@pwd", MySqlDbType.VarChar).Value = PWord
            conn.Open()
            If command.ExecuteNonQuery() = 1 Then
                Return True
            Else
                Return False
            End If
        End Using
    End Function

    Public Shared Function UserNameExists(UName As String) As Boolean
        Using conn As New MySqlConnection(ConStr),
                command As New MySqlCommand("Select `first_name` From `login` Where `username` = @UName", conn)
            command.Parameters.AddWithValue("@UName", UName)
            conn.Open()
            Using reader = command.ExecuteReader
                If reader.HasRows Then
                    Return True
                Else
                    Return False
                End If
            End Using
        End Using
    End Function

End Class