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