VB.NET版“三层登录”实例

学习三层学习近一个月了，对于这块知识的学习，下面我已近期要做的项目机房收费系统的登录界面为例，检验一下我的三层学习：

实现功能：利用三层架构实现简单的用户登录，对于登录成功的用户要添加工作记录。

建立数据库：ComputerCharge_sys，该实例仅用到两张表

表T_User，包括字段：UserID，Password，Level，Status ……

表T_WorkLog，包括字段：UserID，Level，Status，LoginDate，LoginTime ……

Entity层代码实现：

创建实体层Entity程序集，创建封装用户信息类UserInfoEntity和用户工作日志类WorkLoginInfoEntity，该类不属于特定层次，而是专门用于封装数据，方便各层访问。该程序集被各层引用，但它不引用其它各层。

UserInfoEntity类封装表T_User返回的各字段。

'实体类UserInfoEntity：映射数据库表T_User
Public Class UserInfoEntity
    Private _userID As String
    Private _level As String
    Private _status As String
    Private _password As String

    Public Property UserID() As String     '属性用户ID
        Get
            Return _userID
        End Get

        Set(ByVal value As String)
            _userID = value
        End Set
    End Property

    Public Property Level() As String      '属性用户权限
        Get
            Return _level
        End Get
        Set(ByVal value As String)
            _level = value
        End Set
    End Property

    Public Property Status() As String      '属性用户状态
        Get
            Return _status
        End Get
        Set(ByVal value As String)
            _status = value
        End Set
    End Property

    Public Property Password() As String    '属性用户密码
        Get
            Return _password
        End Get
        Set(ByVal value As String)
            _password = value
        End Set
    End Property
End Class

WorkLoginInfoEntity类封装表T_WorkLogo返回的各字段。

'实体类WorkLogInfoEntity：映射数据库表T_WorkLog
Public Class WorkLogInfoEntity
    Private _userID As String
    Private _level As String
    Private _loginDate As String
    Private _loginTime As String
    Private _status As String

    Public Property UserID() As String     '属性用户ID
        Get
            Return _userID
        End Get
        Set(ByVal value As String)
            _userID = value
        End Set
    End Property

    Public Property Level() As String      '属性用户权限
        Get
            Return _level
        End Get
        Set(ByVal value As String)
            _level = value
        End Set
    End Property

    Public Property LoginDate() As String  '属性登录日期
        Get
            Return _loginDate
        End Get
        Set(ByVal value As String)
            _loginDate = value
        End Set
    End Property

    Public Property LoginTime() As String  '属性登录时间
        Get
            Return _loginTime
        End Get
        Set(ByVal value As String)
            _loginTime = value
        End Set
    End Property

    Public Property Status() As String    '属性用户状态
        Get
            Return _status
        End Get
        Set(ByVal value As String)
            _status = value
        End Set
    End Property
End Class

DAL层代码实现：

''' <summary>
''' 创建连接数据库类DbConnStr,方便之后各类连接数据库调用，对今后若更换数据库提供方便。
''' </summary>
''' <remarks></remarks>
Public Class DbConnStr
    Public Shared Function connstring() As String
        connstring = "Server=192.168.24.168;Database=ComputerCharge_sys;User ID=sa;Password=123456"
    End Function
End Class

Imports System.Data.SqlClient
Imports System.Data

''' <summary>
''' 创建数据访问对象UserDAL,访问表Users，返回符合条件调用
''' </summary>
''' <remarks></remarks>
Public Class UserDAL
 
    ' 定义选择用户函数，按传入参数返回T_Users表中指定记录
    Function SelectUser(ByVal user As Entity.UserInfoEntity) As Entity.UserInfoEntity

        Dim conn As New SqlConnection   '创建连接对象
        Dim cmd As New SqlCommand       '创建命令对象
        conn = New SqlConnection(DbConnStr.connstring())  '连接数据库
        cmd.Connection = conn

        '根据实体中的用户名和密码选中记录内容
        cmd.CommandText = "Select * from T_User Where UserID=@UserID and Password=@Password and Status='True'"  '定义SQL语句
        '添加命令参数
        cmd.Parameters.Add(New SqlParameter("@UserID",user.UserID))
        cmd.Parameters.Add(New SqlParameter("@Password",user.Password))
        cmd.CommandType = CommandType.Text
        conn.Open()                   '打开连接

        Dim reader As SqlClient.SqlDataReader
        reader = cmd.ExecuteReader()  '执行查询  

        Dim users As New Entity.UserInfoEntity

        While (reader.Read())          '读取字段
            If users Is Nothing Then
                users = New Entity.UserInfoEntity
            End If
            users.UserID = reader.GetString(reader.GetOrdinal("UserID"))
            users.Level = reader.GetString(reader.GetOrdinal("Level"))
            If (Not reader.IsDBNull(reader.GetOrdinal("Status"))) Then
                users.Status = reader.GetString(reader.GetOrdinal("Status"))
            End If
        End While
        conn.Close()
        Return users    '返回查询结果

    End Function
End Class

Imports System.Data.SqlClient

''' <summary>
'''  创建数据库访问类工作日志WorkLogDAL,访问T_WorkLog,对于登录成功的用户插入工作日志记录。
''' </summary>
''' <remarks></remarks>
Public Class WorkLogDAL
    Public Function FillWorkLog(ByVal userWorkLog As Entity.WorkLogInfoEntity) As Boolean
        Dim conn As SqlConnection
        Dim cmd As SqlCommand

        Dim connStr As String = "server=192.168.24.168;database=ComputerCharge_sys;uid=sa;pwd=123456 "
        conn = New SqlConnection(connStr)
        cmd = conn.CreateCommand

        cmd.CommandText = "Insert INTO T_WorkLog(UserID,Level,LoginDate,LoginTime,Status)values(@UserID,@Level,@LoginDate,@LoginTime,@Status)"
        cmd.Parameters.Add(New SqlParameter("@UserID",userWorkLog.UserID))
        cmd.Parameters.Add(New SqlParameter("@Level",userWorkLog.Level))
        cmd.Parameters.Add(New SqlParameter("@Status",userWorkLog.Status))
        userWorkLog.LoginDate = Format(Now,"yyyy/MM/dd")
        userWorkLog.LoginTime = Format(Now,"HH:mm:ss")
        cmd.Parameters.Add(New SqlParameter("@LoginDate",userWorkLog.LoginDate))
        cmd.Parameters.Add(New SqlParameter("@LoginTime",userWorkLog.LoginTime))
        conn.Open()

        Dim num As Integer           'num，表示插入命令的执行结果
        Dim flag As New Boolean      'flag，表示FillWorkLog（）函数的返回结果

        num = cmd.ExecuteNonQuery()  '执行插入命令

        '当num大于0，表示插入数据成功，否则失败。
        If num > 0 Then
            flag = True
        Else
            flag = False
        End If
        conn.Close()
        Return flag
    End Function
End Class

BLL层分析

''' <summary>
''' 创建登录类，实现登录过程的逻辑处理
''' </summary>
''' <remarks></remarks>
Public Class LoginBLL
    ' 定义登录函数,验证用户名和密码是否正确 
    Function UserLogin(ByVal user As Entity.UserInfoEntity) As Entity.UserInfoEntity
        Dim uDal As New DAL.UserDAL             '引用DAL层，声明必要类
        Dim users As New Entity.UserInfoEntity  '引用Entity层，实例化UserInfoEntity类
        Dim wDal As New DAL.WorkLogDAL          '引用DAL层，实例化WorkLogDAL类

        users = uDal.SelectUser(user)
        Return users

    End Function
    '定义添加工作日志函数
    Function FillWorkLog(ByVal userWorkLog As Entity.WorkLogInfoEntity) As Boolean
        Dim worklog As New DAL.WorkLogDAL  '实例化DAL层的WorkLogDAL类
        Dim flag As Boolean                'flag用于定义DAL层的方法FillWorkLog的返回结果

        flag = worklog.FillWorkLog(userWorkLog)
        Return flag

    End Function
End Class

UI分析

1.创建系统登录界面：

2.编写登录事件代码：

Public Class LoginUI
    Private Sub btnLogin_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles btnLogin.Click

        Dim mgr As New BLL.LoginBLL               '实例化业务逻辑层LoginBLL类
        Dim user As New Entity.UserInfoEntity     '实例化实体类UserInfoEntity
        Dim users As Entity.UserInfoEntity        '实例化实体类UserInfoEntity，user:用于BLL层的方法UserLogin()返回的数据类型（实体类型）。
        Dim enWorkLog As New Entity.WorkLogInfoEntity
        Dim workLog As New BLL.LoginBLL
        Dim flag As Boolean

        '将界面中的数据传入给实体中UserInfoEntity类的属性值
        user.UserID = txtUserName.Text.Trim()
        user.Password = txtPassword.Text.Trim()

        '将界面中的数据传入给实体中UserInfoEntity类的属性值
        enWorkLog.UserID = txtUserName.Text.Trim()

        '界面业务逻辑：判断用户名和密码不能为空
        If txtUserName.Text = "" Then
            MessageBox.Show("用户名不能为空")
            Return
        End If

        If txtPassword.Text = "" Then
            MessageBox.Show("密码不能为空！")
            Return
        End If

        Try
            '引用BLL层，执行用户登录业务逻辑
            users = mgr.UserLogin(user)

            If (users.UserID Is Nothing And users.Password Is Nothing) Then
                MessageBox.Show("登录失败，用户名和密码不匹配")
                Return
            Else
                enWorkLog.Level = users.Level
                enWorkLog.Status = users.Status

                '引用BLL层，执行添加工作日志业务逻辑
                flag = mgr.FillWorkLog(enWorkLog)
                'If (flag = False) Then
                '    MessageBox.Show("登录成功，插入数据失败")
                '    Return
                'Else
                '    MessageBox.Show("插入数据成功")
                'End If
                MessageBox.Show("登录成功！ 登录用户：" + user.UserID)
            End If
        Catch ex As Exception
            MessageBox.Show(ex.Message())
        End Try
    End Sub
End Class

此项目就此完成，系统模块如下图：

小结：三层架构用于用户业务逻辑复杂且需要存储数据的系统架构，其目的主要是降低系统之间的耦合，根据各层之间的引用，开发者可各层关注来予以各个层次的设计，明显改善系统的可维护性，增强系统优化的目的性。

（编辑：李大同）

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