解析三层架构(2)----分层究竟分出了那些东西

在上篇文章写到我们为什么要分层.有很多读者提出来很多宝贵的意见.让我受益匪浅,深深的感觉到自己的水平"还有很大的提升空间".首先感谢这些朋友们,我会进一步总结完善自己的想法.

截取了部分朋友的留言,感谢他们:

这次我用对比的方式描述一下,分层到底分出了什么.俗话说:有分必有合,那么它是把什么合到了一起.

首先写出两个没有分层的demo:

<1>查询信息demo

   1: Public Class Form2

   2:     Private sqlCon As String = "Data Source=LSH;Initial Catalog=ComputerLab;User ID=sa;Password=123456"

   3:     '查询数据库信息信息

   4:     Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

   5:  

   6:         Dim conStr As New SqlConnection '数据库连接对象

   7:         Dim sqlCom As SqlCommand        '数据库执行对象

   8:         Dim Res As DialogResult         '消息提示框返回类型

   9:         Dim dr As SqlDataReader         'dataReader对象

  10:         Dim dt As New DataTable         'Datatable对象

  11:  

  12:         Dim sql As String = "select * from TableName where Name=@name"                   'sql插入语句

  13:         conStr.ConnectionString = sqlCon                                '给数据库连接对象赋值

  14:         sqlCom = New SqlCommand(sql, conStr)                            '给数据库执行对象赋值

  15:         sqlCom.Parameters.Add("@name", SqlDbType.VarChar, TextBox1.Text)    '给sql语句参数赋值

  16:  

  17:         Res = MessageBox.Show("是否添加", "提示", MessageBoxButtons.OKCancel)

  18:         '判断是否查询

  19:         If Res = DialogResult.Yes Then

  20:             Try

  21:                 conStr.Open()

  22:                 dr = sqlCom.ExecuteReader    '执行查询语句

  23:                 dt.Load(dr)

  24:             Catch ex As Exception

  25:                 Throw ex

  26:             Finally

  27:                 If Not IsNothing(conStr) Then   '如果数据库打开,则关闭数据库

  28:                     conStr.Close()

  29:                 End If

  30:             End Try

  31:         End If

  32:  

  33:         MsgBox(dt.Rows.Count)   '显示查询到的行数

  34:     End Sub

<2>添加信息demo

   1: Public Class Form1

   2:     Private sqlCon As String = "Data Source=LSH;Initial Catalog=ComputerLab;User ID=sa;Password=123456"

   3:     '向数据库添加信息

   4:     Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

   5:         Dim bln As Boolean = False      '存储返回值

   6:         Dim conStr As New SqlConnection '数据库连接对象

   7:         Dim sqlCom As SqlCommand        '数据库执行对象

   8:         Dim Res As DialogResult         '消息提示框返回类型

   9:  

  10:         Dim sql As String = "insert into TableName(Name) value(@Name)"  'sql插入语句

  11:         conStr.ConnectionString = sqlCon                                '给数据库连接对象赋值

  12:         sqlCom = New SqlCommand(sql, conStr)                            '给数据库执行对象赋值

  13:         sqlCom.Parameters.Add("@Name", SqlDbType.VarChar, TextBox1.Text) '给sql语句参数赋值

  14:  

  15:         Res = MessageBox.Show("是否添加", "提示", MessageBoxButtons.OKCancel)

  16:         '判断是否同意插入

  17:         If Res = DialogResult.Yes Then

  18:             Try

  19:                 conStr.Open()

  20:                 bln = sqlCom.ExecuteNonQuery    '执行插入语句

  21:             Catch ex As Exception

  22:                 bln = False

  23:             Finally

  24:                 If Not IsNothing(conStr) Then   '如果数据库打开,则关闭数据库

  25:                     conStr.Close()

  26:                 End If

  27:             End Try

  28:         End If

  29:  

  30:         MsgBox(bln) '提示返回信息

  31:     End Sub

  32: End Class

上面的两个没有分层的代码,当然在功能的实现上是完全没有问题.但是这样设计带来了很多的危机:

(1):写这个模块的人必须是一个能力非常强的人,因为他需要操作数据库,理解业务逻辑

(2):如果有另为一个模块需要这两个操作数据库的方法,只能重写或者调用该窗体下的方法.

(3):如果业务逻辑稍有变动,就需要拆开这个模块,重新编写,对于重新设计的人来说这个模块的所有设计都是可见的,很是不安全.

(4):如果要更换或者改动数据库,结果就是每一个模块都要重新编写

(5):如果有另为一个和这个相似的工程,想要复用以前的东西,难度很大

对于一个公司来说,当然不希望发生这样的事情.所以,合理的分层,降低系统的耦合性是必要的.

第一步:把数据库操作提取出来.

对每一个表,把完全对他的操作单独写成类也就是我们的DAO,数据访问类

每一个表对应一个DAO,每个DAO里面包含该数据库的所有增,删,查,改操作.这样做的好处就是对数据库的操作完全独立,达到功能单一.降低了和其他模块的耦合,写代码的时候,程序员不需要了解业务逻辑.

而且,在维护上和扩展上,如果对数据库改动,就会有针对性的去修改DAO.

当然,在设计的时候,我们尽量去封装不变的操作,这样不但能减少代码量,而且能达到很好的复用效果.在数据库操作中,对于数据库的打开,执行,关闭基本上都是一样的.所以我们单独提取出来sqlHelper(数据库助手类)

 

   1: Imports System.Data.SqlClient

   2: Imports System.Configuration

   3:  

   4: ''' <summary>

   5: ''' 运行数据库

   6: ''' </summary>

   7: Public Class SqlHelp

   8:     Private cmd As SqlCommand   'sqlcommand对象

   9:     Private con As SqlConnection    'sqlconnection对象

  10:     Private dr As SqlDataReader     'sqlDataReader对象

  11:     ''' <summary>

  12:     ''' 获取连接字符串

  13:     ''' </summary>

  14:     ''' <returns>连接字符串</returns>

  15:     ''' <remarks></remarks>

  16:     Public Function GetCon() As SqlConnection

  17:         Dim conStr As String

  18:         conStr = System.Configuration.ConfigurationManager.AppSettings("ConnStr")

  19:  

  20:         con = New SqlConnection

  21:         con.ConnectionString = conStr

  22:  

  23:         '打开数据库

  24:         If (con.State = ConnectionState.Closed) Then

  25:             con.Open()

  26:         End If

  27:  

  28:         Return con

  29:  

  30:     End Function

  31:  

  32:     ''' <summary>

  33:     ''' 增 删 改方法

  34:     ''' </summary>

  35:     ''' <param name="sqlStr">数据库语句 活存储过程名</param>

  36:     ''' <param name="Param">参数数组</param>

  37:     ''' <param name="commandType">数据库字符串 或者存储过程名 类型</param>

  38:     Public Function ExecuteNonQuery(ByVal sqlStr As String, ByVal Param() As SqlParameter, ByVal commandType As CommandType) As Boolean

  39:  

  40:         cmd = New SqlCommand(sqlStr, Me.GetCon)

  41:         cmd.CommandType = commandType

  42:  

  43:         '添加参数

  44:         If Param IsNot Nothing Then

  45:             cmd.Parameters.AddRange(Param)

  46:         End If

  47:  

  48:         '执行语句

  49:         Try

  50:             Return CBool(cmd.ExecuteNonQuery)

  51:         Catch ex As Exception

  52:             Return False

  53:         Finally

  54:             If Not IsNothing(con) Then

  55:                 con.Close()

  56:             End If

  57:         End Try

  58:  

  59:     End Function

  60:  

  61:     ''' <summary>

  62:     ''' 查询

  63:     ''' </summary>

  64:     ''' <param name="sqlStr">sql语句 或者存储过程名</param>

  65:     ''' <param name="Param">参数数组</param>

  66:     ''' <param name="commandType">执行类型</param>

  67:     Public Function ExecuteQuery(ByVal sqlStr As String, ByVal Param() As SqlParameter, ByVal commandType As CommandType) As DataTable

  68:         Dim dt As New DataTable

  69:         cmd = New SqlCommand(sqlStr, Me.GetCon)

  70:         cmd.CommandType = commandType

  71:  

  72:         '添加参数

  73:         If Param IsNot Nothing Then

  74:             cmd.Parameters.AddRange(Param)

  75:         End If

  76:  

  77:         '执行语句

  78:         Try

  79:             dr = cmd.ExecuteReader

  80:             dt.Load(dr)

  81:         Catch ex As Exception

  82:             Return Nothing

  83:         Finally

  84:             If Not IsNothing(con) Then

  85:                 con.Close()

  86:             End If

  87:         End Try

  88:         Return dt

  89:     End Function

提取后数据库访问层代码如下: 

   1: Imports SqlHelper

   2: Imports System.Data.SqlClient

   3: Public Class DAL

   4:     Private sqlHelper As New SqlHelp

   5:     ''' <summary>

   6:     ''' 查询记录

   7:     ''' </summary>

   8:     ''' <param name="strSelect">关键字</param>

   9:     ''' <returns>记录集</returns>

  10:     ''' <remarks></remarks>

  11:     Public Function SelectInfo(ByVal strSelect As String) As DataTable

  12:         'sql查询语句

  13:         Dim sql As String = "select * from TableName where Name=@name"

  14:         '向sql参数中添加实参

  15:         Dim Para() As SqlParameter = {New SqlParameter("@name", strSelect)}

  16:         '调用sqlhelper执行数据库操作

  17:         Return sqlHelper.ExecuteQuery(sql, Para, Data.CommandType.Text)

  18:     End Function

  19:     ''' <summary>

  20:     ''' 添加记录

  21:     ''' </summary>

  22:     ''' <param name="strAdd">记录信息</param>

  23:     ''' <returns>是否成功</returns>

  24:     ''' <remarks></remarks>

  25:     Public Function AddInfo(ByVal strAdd As String) As Boolean

  26:         'sql插入语句

  27:         Dim sql As String = "insert into TableName(Name) value(@Name)"

  28:         '向sql参数中添加实参

  29:         Dim Para() As SqlParameter = {New SqlParameter("@name", strAdd)}

  30:         '调用sqlhelper执行数据库操作

  31:         Return sqlHelper.ExecuteNonQuery(sql, Para, Data.CommandType.Text)

  32:     End Function

  33: End Class

第二:根据业务逻辑,个人习惯和用例相对应,把相关的逻辑判断,比如添加记录在什么情况下判断,添加前要判断记录是否存在等放到BLL层.

但是对于数据的有效性校验一般还是放在UI层,也可以有其他更好的方法,这些我在以后会总结出来.

代码如下:

   1: Public Class BLL

   2:     Private dal As New DAL

   3:     ''' <summary>

   4:     ''' 业务逻辑层,添加方法

   5:     ''' </summary>

   6:     ''' <param name="strAdd">添加信息</param>

   7:     ''' <remarks></remarks>

   8:     Public Sub Add(ByVal strAdd As String)

   9:         '定义用于存储查询结果的记录集

  10:         Dim dt As New DataTable

  11:         '执行查询,判断添加的信息是否已经存在

  12:         dt = dal.SelectInfo(strAdd)

  13:         If dt.Rows.Count > 0 Then

  14:             Throw New Exception("记录已存在")

  15:         Else

  16:             '添加记录,返回是否成功

  17:             If dal.AddInfo(strAdd) = True Then

  18:                 Throw New Exception("添加成功")

  19:             Else

  20:                 Throw New Exception("添加失败")

  21:             End If

  22:         End If

  23:  

  24:     End Sub

  25:  

  26: End Class

第三:剩下的UI层里,除了判断数据有效性以为,只要调用bll的添加方法就可以了.这样制作UI的人就会减轻了很大的压力,让他们专心做美工或者其他.

代码如下:

   1: Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click

   2:         Dim bll As New BLL

   3:         '调用bll层添加方法

   4:         Try

   5:             bll.Add(TextBox1.Text)

   6:         Catch ex As Exception

   7:             '显示添加结果给用户

   8:             MessageBox.Show(ex.Message)

   9:         End Try

  10:     End Sub

当然三层方式还有其他一些技巧,比如为DAL加一层接口,用抽象工厂加反射的方法实现数据库的灵活操作,替换.这里先不叙述.

上述都是个人的一点总结,欢迎大家指导

 

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