【机房重构】组合查询之模板方法

      在第一次敲机房的时候组合查询就是一个很值得学习的问题，在这次机房个人重构又重新的了解学习了一下这个功能，感觉比第一次好了很多，也是熟悉了很多的东西，这次我用了设计模式中的模板方法模式。感觉棒棒的！来分享一下！！

      模板方法模式：

      定义一个操作中的算法的骨架，而将一些步骤延迟到子类中。模板方法使得子类可以不改变一个算法的结构即可重定义该算法的某些特定步骤。

    模板方法模式（TemplateMethod）结构图

     

     

  组合查询

      1、建立模板父窗体 

Private Sub Father1_Load(sender As Object, e As EventArgs) Handles MyBase.Load        '将参数传递给实体，赋初值          '字段名          GroupInquire.CmbName1 = ""        GroupInquire.CmbName2 = ""        GroupInquire.CmbName3 = ""        '操作符          CmbMark1.Items.Add(">")        CmbMark1.Items.Add("<")        CmbMark1.Items.Add("=")        CmbMark1.Items.Add("<>")        CmbMark2.Items.Add(">")        CmbMark2.Items.Add("<")        CmbMark2.Items.Add("=")        CmbMark2.Items.Add("<>")        CmbMark3.Items.Add(">")        CmbMark3.Items.Add("<")        CmbMark3.Items.Add("=")        CmbMark3.Items.Add("<>")        '关系          CmbRelation1.Items.Add("与")        CmbRelation1.Items.Add("或")        CmbRelation2.Items.Add("与")        CmbRelation2.Items.Add("或")        CmbName2.Enabled = False        CmbName3.Enabled = False        CmbMark2.Enabled = False        CmbMark3.Enabled = False        CmbRelation2.Enabled = False        txtContent2.Enabled = False        txtContent3.Enabled = False        Dim i As Integer        For i = 0 To dgv.Columns.Count - 1            dgv.Columns(i).Width = DataGridViewAutoSizeColumnMode.AllCells    '调整列宽为根据内容自动调整         Next    End Sub    '查询      Private Sub btnQuery_Click(sender As Object, e As EventArgs) Handles btnQuery.Click        If CmbRelation1.Text = "" Then            If CmbName1.Text = "" Or CmbName1.Text = "" Or txtContent1.Text = "" Then                MsgBox("第一行查询条件不能为空，请完善", , "提示")                Exit Sub            End If        End If        If CmbRelation1.Text <> "" Then            If CmbName1.Text = "" Or CmbName1.Text = "" Or txtContent1.Text = "" Or CmbName2.Text = "" Or CmbMark2.Text = "" Or txtContent2.Text = "" Then                MsgBox("所输入的查询条件不能为空，请完善", , "提示")                Exit Sub            End If        End If        If CmbRelation2.Text <> "" Then            If CmbName1.Text = "" Or CmbName1.Text = "" Or txtContent1.Text = "" Or CmbName2.Text = "" Or CmbMark2.Text = "" Or txtContent2.Text = "" Or CmbName3.Text = "" Or CmbMark3.Text = "" Or txtContent3.Text = "" Then                MsgBox("所输入的查询条件不能为空，请完善", , "提示")                Exit Sub            End If        End If        '将参数传给实体          GroupInquire.DbName = GetdbName()        GroupInquire.CmbName1 = GetEnglish(CmbName1.Text)        GroupInquire.CmbName2 = GetEnglish(CmbName2.Text)        GroupInquire.CmbName3 = GetEnglish(CmbName3.Text)        GroupInquire.CmbMark1 = CmbMark1.Text.Trim        GroupInquire.CmbMark2 = CmbMark2.Text.Trim        GroupInquire.CmbMark3 = CmbMark3.Text.Trim        GroupInquire.TxtContent1 = txtContent1.Text.Trim        GroupInquire.TxtContent2 = txtContent2.Text.Trim        GroupInquire.TxtContent3 = txtContent3.Text.Trim        GroupInquire.CmbRelation1 = GetEnglish(CmbRelation1.Text)        GroupInquire.CmbRelation2 = GetEnglish(CmbRelation2.Text)        Dim dt As New DataTable        Dim Generalfacade As New Facade.FaFather   '实例化外观层          dt = Generalfacade.GroupFather(GroupInquire)        If (dt.Rows.Count = 0) Then            MsgBox("没有符合条件的记录", , "提示")            Exit Sub        Else            Call Todgv(GroupInquire)  '把表显示到datagridview中           End If    End Sub    '模板方法，定义虚函数GetEnglish，查询字段转化为数据库字段       Public Overridable Function GetEnglish(cmbName As String) As String        Return ""    End Function    '获得数据库表名        Protected Overridable Function GetdbName() As String        Return ""    End Function    '把表显示到datagridview中      Protected Overridable Sub Todgv(ByVal comQueryEntity As Entity.GroupInquire)    End Sub    '第一个组合关系是否为空      Private Sub CmbRelation1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles CmbRelation1.SelectedIndexChanged        If CmbRelation1.Text = "" Then            CmbName2.Enabled = False            CmbName3.Enabled = False            CmbMark2.Enabled = False            CmbMark3.Enabled = False            CmbRelation2.Enabled = False            txtContent2.Enabled = False            txtContent3.Enabled = False        Else            CmbName2.Enabled = True            CmbMark2.Enabled = True            CmbRelation2.Enabled = True            txtContent2.Enabled = True        End If    End Sub    ' 第二个组合关系是否为空       Private Sub CmbRelation2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles CmbRelation2.SelectedIndexChanged        If CmbRelation2.Text = "" Then            CmbName3.Enabled = False            CmbMark3.Enabled = False            txtContent3.Enabled = False        Else            CmbName3.Enabled = True            CmbMark3.Enabled = True            txtContent3.Enabled = True        End If    End Sub    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click        '清空        CmbName1.Text = ""        CmbName2.Text = ""        CmbName3.Text = ""        CmbMark3.Text = ""        CmbMark2.Text = ""        CmbMark1.Text = ""        txtContent3.Text = ""        txtContent1.Text = ""        txtContent2.Text = ""        CmbRelation1.Text = ""        CmbRelation2.Text = ""        'dgv.Rows.Remove(dgv.All)    End Sub

   2、建立子窗体

     如下图建立子窗体，然后选择要继承的父窗体，在子窗体里重写类和方法就OK了，只需在U层这一层写就行。我们来用学生基本信息查询为例。    

     子窗体的代码：

Private Sub frmStuBaseInfo_Load(sender As Object, e As EventArgs) Handles MyBase.Load        '赋初值          CmbName1.Items.Add("学号")        CmbName1.Items.Add("姓名")        CmbName1.Items.Add("性别")        CmbName1.Items.Add("专业")        CmbName1.Items.Add("年级")        CmbName1.Items.Add("班级")

        CmbName2.Items.Add("学号")        CmbName2.Items.Add("姓名")        CmbName2.Items.Add("性别")        CmbName2.Items.Add("专业")        CmbName2.Items.Add("年级")        CmbName2.Items.Add("班级")        CmbName3.Items.Add("学号")        CmbName3.Items.Add("姓名")        CmbName3.Items.Add("性别")        CmbName3.Items.Add("专业")        CmbName3.Items.Add("年级")        CmbName3.Items.Add("班级")    End Sub    '把加载的汉字转换成数据库的字段       Public Overrides Function GetEnglish(cmbName As String) As String        Select Case cmbName            Case "学号"                GetEnglish = "chr_StudentNo"            Case "姓名"                GetEnglish = "chr_StudentName"            Case "性别"                GetEnglish = "chr_Sex"            Case "专业"                GetEnglish = "chr_Department"            Case "年级"                GetEnglish = "chr_Grade"            Case "班级"                GetEnglish = "chr_Class"            Case "与"                GetEnglish = "and"            Case "或"                GetEnglish = "or"            Case Else                GetEnglish = ""        End Select    End Function    '传数据库表名       Protected Overrides Function GetdbName() As String        Return "T_Student"    End Function    '查询并把数据显示到datagridview中      Protected Overrides Sub Todgv(ByVal comQueryEntity As Entity.GroupInquire)        Dim table As New DataTable        Dim father As New Father1        Dim GeneralFacade As New Facade.FaFather        Try           table = GeneralFacade.GroupFather(comQueryEntity)            If table.Rows.Count = 0 Then                table.Clear()                dgv.DataSource = Nothing                dgv.Refresh()            Else                dgv.DataSource = table                dgv.Columns(0).Visible = False                dgv.Columns(0).HeaderText = "卡号"                dgv.Columns(1).HeaderText = "学号"                dgv.Columns(2).HeaderText = "姓名"                dgv.Columns(3).HeaderText = "专业"                dgv.Columns(4).HeaderText = "性别"                dgv.Columns(5).HeaderText = "年级"                dgv.Columns(6).HeaderText = "班级"                'dgv.Columns(7).HeaderText = "注释"                dgv.Columns(7).HeaderText = "注册日期"                dgv.Columns(8).HeaderText = "注册时间"         End If        Catch ex As Exception            MsgBox(ex.Message, vbOKOnly, "提示")        End Try    End Sub

   3、DAL层数据库查询

   Public Function IGroupCheck(father As Entity.GroupInquire) As DataTable Implements IGroupInquire.IGroupCheck        Dim sql As String        Dim table As DataTable        sql = "select * from " & father.DbName & " where "        If Trim(father.CmbRelation1) = "" Then  '有一组查询条件              sql = sql & father.CmbName1 & father.CmbMark1 & "'" & father.TxtContent1 & "'"        Else            If Trim(father.CmbRelation2) = "" Then '有两组查询条件                  sql = sql & father.CmbName1 & father.CmbMark1 & "'" & father.TxtContent1 & "'" & father.CmbRelation1 & " " & father.CmbName2 & father.CmbMark2 & "'" & father.TxtContent2 & "'"            Else                sql = sql & father.CmbName1 & father.CmbMark1 & "'" & father.TxtContent1 & "'" & father.CmbRelation1 & " " & father.CmbName2 & father.CmbMark2 & "'" & father.TxtContent2 & "'" & father.CmbRelation2 & " " & father.CmbName3 & father.CmbMark3 & "'" & father.TxtContent3 & "'"            End If        End If        '模板的无参查询          table = sqlHelper.ExecSelect(sql, CommandType.Text)        Return table    End Function