mysql - VB.net block 复式输入

Question

这是记录所有状态(IN/OUT)的事件表:

+--------------------------------------------------+-----------------+
| Event_ID | User_BannerID  | Group_ID | Timestamp | Status | Creator|
+----------+----------------+----------+-----------+--------+--------+
|          |                |          |           |        |        |
|          |                |          |           |        |        |
+----------+----------------+----------+-----------+--------+--------+ 

所以我使用 vb.net 和 mysql 制作一个 checkin checkout 程序。我想知道是否有一个代码可以放在某个地方，就像用户打开应用程序时，他/她必须先登录才能注销，如果他们打开应用程序并且已经登录，则他们无法再次登录必须先注销，然后才能再次注销。

Imports MySql.Data.MySqlClient
Imports System.Data

Public Class frmMain
    Private myConnString As String
    Private myUserID As String

    Public WriteOnly Property connectionString() As String
        Set(ByVal value As String)
            myConnString = value
        End Set
    End Property

    Public WriteOnly Property UserID() As String
        Set(ByVal value As String)
            myUserID = value
        End Set
    End Property

    Private Sub refreshStatus(ByRef statusView As DataGridView)
        Dim conn As New MySqlConnection
        Dim myCommand As New MySqlCommand
        Dim myAdapter As New MySqlDataAdapter
        Dim myData As New DataTable
        Dim SQL As String


        SQL = "SELECT CONCAT(u.lastname, ', ', u.firstname) AS Name, ug.group_name AS Class, DATE_FORMAT(e.timestamp,'%b %d %Y - %r')AS DateTime, e.status AS Status " _
             & "FROM event e, user u, user_group ug " _
             & "WHERE(e.user_bannerid = u.user_bannerid) " _
             & "AND e.group_id = ug.group_id " _
             & "AND ug.user_bannerid = ?userID " _
             & "AND event_id IN " _
             & "( " _
             & "Select MAX(e.event_id) " _
             & "FROM event e " _
             & "GROUP BY e.user_bannerid " _
             & ") " _
             & "ORDER BY datetime"



        conn.ConnectionString = myConnString

        Try
            conn.Open()

            Try
                myCommand.Connection = conn
                myCommand.CommandText = SQL
                myCommand.Parameters.Add("?userID", myUserID)

                myAdapter.SelectCommand = myCommand
                myAdapter.Fill(myData)

                dgvStatus.DataSource = myData
                dgvStatus.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill
            Catch myerror As MySqlException
                MsgBox("There was an error reading from the database: " & myerror.Message)
                End Try
        Catch myerror As MySqlException
            MessageBox.Show("Error connecting to the database: " & myerror.Message)
        Finally
            If conn.State <> ConnectionState.Closed Then conn.Close()
            End Try

    End Sub

    Private Sub frmMain_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        cboStatus.Items.Add("In")
        cboStatus.Items.Add("Out")
        cboStatus.SelectedIndex = 0

        dgvStatus.ReadOnly = True
        refreshStatus(dgvStatus)

        Dim conn As New MySqlConnection
        Dim myCommand As New MySqlCommand
        Dim myAdapter As New MySqlDataAdapter
        Dim myData As New DataTable
        Dim SQL As String


        SQL = "SELECT ug.group_id, ug.group_name " _
         & "FROM attendance.user_group ug " _
         & "WHERE user_bannerid = ?userID and level_id is NULL "

        conn.ConnectionString = myConnString

        Try
            conn.Open()

            Try
                myCommand.Connection = conn
                myCommand.CommandText = SQL
                myCommand.Parameters.Add("?userID", myUserID)


                myAdapter.SelectCommand = myCommand
                myAdapter.Fill(myData)

                cboClass.DataSource = myData
                cboClass.DisplayMember = "group_name"
                cboClass.ValueMember = "group_id"
            Catch myerror As MySqlException
                MsgBox("There was an error reading from the database: " & myerror.Message)
            End Try
        Catch myerror As MySqlException
            MessageBox.Show("Error connecting to the database: " & myerror.Message)
        Finally
            If conn.State <> ConnectionState.Closed Then conn.Close()
        End Try
    End Sub

    Private Sub cmdUpdate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdUpdate.Click
        Dim conn As New MySqlConnection
        Dim myCommand As New MySqlCommand

        conn.ConnectionString = myConnString

        myCommand.Connection = conn
        myCommand.CommandText = "INSERT INTO event(user_bannerid, group_id, timestamp, status, creator)" _
         & "VALUES(?UserID, ?GroupID, NOW(), ?Status, ?Creator)"

        myCommand.Parameters.Add("?UserID", myUserID)
        myCommand.Parameters.Add("?GroupID", cboClass.SelectedValue)
        myCommand.Parameters.Add("?Status", cboStatus.SelectedItem)
        myCommand.Parameters.Add("?Creator", myUserID)

        Try
            conn.Open()
            myCommand.ExecuteNonQuery()
            MessageBox.Show("Status Successfully Updated")
        Catch myerror As MySqlException
            MsgBox("There was an error updating the database: " & myerror.Message)
        End Try
        refreshStatus(dgvStatus)
    End Sub
    Private Sub cmdExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdExit.Click
        Dim oForm As frmLogin
        oForm = New frmLogin()
        frmLogin.Show()
        oForm = Nothing
        Me.Hide()
    End Sub

    Private Sub frmLogin_Click(ByVal sender As System.Object, ByVal e As System.Windows.Forms.FormClosedEventArgs) Handles MyBase.FormClosed
        Dim oForm As frmLogin
        oForm = New frmLogin()
        frmLogin.Show()
        oForm = Nothing
        Me.Hide()
    End Sub
End Class

Answer 1

如果用户已经登录，为什么不在再次登录之前自动注销用户呢？如果您发现他们之前已登录，您可以告诉他们(通过消息框或其他方式)他们已自动退出之前的 session 。

更新

在审查您的问题和代码时，我认为您依靠事件日志提供用户状态让自己的生活变得太困难。事件日志应该仅用于记录离散事件，而不是用于确定用户的状态。

我建议您向用户表添加一个状态字段。这将始终存储用户的当前状态(进入或退出)。

当用户打开您的应用程序时，您将进行一个简单的检查:用户的状态是什么？如果用户已登录，则向用户显示“注销”按钮。如果用户未登录，则向他们显示“注销”按钮。不要让他们从下拉列表中选择自己的状态，因为我可以保证他们会把事情搞砸。

如果用户已登录，但想再次登录，可以按注销按钮。您将使用新状态更新用户表并记录事件，然后禁用“注销”按钮并启用“登录”按钮。当他们按下登录按钮时，您将更新用户状态并记录新事件。

作为一个选项，如果用户在启动应用程序时当前已登录，您可以(从事件日志中或作为用户记录中的单独字段)显示他们上次登录的时间，这样他们就不会混淆关于为什么向他们显示注销按钮。

使用特定代码更新

Private Const STATUS_IN As String = "In"
Private Const STATUS_OUT As String = "Out"

Private Sub frmMain_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    ' Disable the buttons to start
    btnLogin.Enabled = False
    btnLogout.Enabled = False

    Dim sCurrentStatus As String

    ' Get the user's current status
    sCurrentStatus = GetUserStatus()

    ' And update the buttons based on this status change
    Call UpdateButtonsForStatusChange(sCurrentStatus)
End Sub

Private Sub UpdateButtonsForStatusChange(sStatus As String)

    Dim fLoggedIn As Boolean

    ' Determine whether or not the user is logged in based on the status
    fLoggedIn = sStatus.Equals(STATUS_IN, StringComparison.InvariantCultureIgnoreCase)

    ' If the user is NOT logged in, enable the login button
    btnLogin.Enabled = Not fLoggedIn
    ' If the user IS logged in, enable the logout button
    btnLogout.Enabled = fLoggedIn

End Sub

Private Sub btnLogin_Click(sender As System.Object, e As System.EventArgs) Handles btnLogin.Click
    ' Indicate that the user is logging in
    Call HandleButtonClick(STATUS_IN)
End Sub

Private Sub btnLogout_Click(sender As System.Object, e As System.EventArgs) Handles btnLogout.Click
    ' Indicate that the user is logging out
    Call HandleButtonClick(STATUS_OUT)
End Sub

Private Sub HandleButtonClick(sNewStatus As String)

    ' Update the database with the user's new status
    Call UpdateUserStatus(sNewStatus)
    ' And update the buttons based on this status change
    Call UpdateButtonsForStatusChange(sNewStatus)

End Sub

Private Function GetUserStatus() As String

    ' ToDo: Add your code to get the user's current status here

End Function

Private Sub UpdateUserStatus(sNewStatus As String)

    ' ToDo: Add your code to save the user's current status here

End Sub