机房重构——组合查询

     机房收费系统中有三个功能用到了“组合查询”——可以查询1到3个条件的数据。这三胞胎长得是很像很像滴，上图：



     学习了设计模式，但是到实际用的时候还是不会啊，看了很多资料博客，在这里实践了一把——用模板方法模式

分析：三个的窗体是一样的，查询的表不一样，字段也就不一样，所以要在抽象出来的父窗体中写一个基本框架，在各自的子窗体中赋值。

1.窗体

父窗体写好以后，子窗体创建：



以“学生信息维护”为例，子窗体与父窗体长的一样，创建好之后控件上有小锁标志，会发现，它是不能动的（事件不可用）



u层代码如下：这里要写一个虚方法，用来返回字段名，在各个子窗体中就可以重写来给字段赋值了

Public Class FrmPowerQuery

Private Sub BtnClear_Click(sender As Object, e As EventArgs) Handles BtnClear.Click
CmbActor1.Text = ""
CmbActor2.Text = ""
CmbActor3.Text = ""
CmbFieldName1.Text = ""
CmbFieldName2.Text = ""
CmbFieldName3.Text = ""
CmbRelation1.Text = ""
CmbRelation2.Text = ""
TxtMessage1.Text = ""
TxtMessage2.Text = ""
TxtMessage3.Text = ""
DataGridView1.DataSource = ""
End Sub

Private Sub BtnOK_Click(sender As Object, e As EventArgs) Handles BtnOK.Click
If CmbActor1.Text.Trim = "" Or CmbFieldName1.Text.Trim = "" Or TxtMessage1.Text.Trim = "" Then
MsgBox("请将第一行查询信息补充完整")
Exit Sub
End If

If CmbRelation1.Text <> "" And (CmbActor2.Text.Trim = "" Or CmbFieldName2.Text.Trim = "" Or TxtMessage2.Text.Trim = "") Then
MsgBox("应该将第二条查询信息补充完整")
Exit Sub
End If
If CmbRelation2.Text <> "" And (CmbActor3.Text.Trim = "" Or CmbFieldName3.Text.Trim = "" Or TxtMessage3.Text.Trim = "") Then
MsgBox("应将第三条查询信息补充完整")
Exit Sub
End If

'实体赋值
Dim Queryinfo As New Entity.ePowerQueryEntity
Queryinfo.DBName = getDTName() '获取数据库名
Queryinfo.CmbActor1 = SameAsTable(CmbActor1.Text.Trim)  '获得查询的字段名并且转化成sql语句可以识别的语句
Queryinfo.CmbActor2 = SameAsTable(CmbActor2.Text.Trim)
Queryinfo.CmbActor3 = SameAsTable(CmbActor3.Text.Trim)
Queryinfo.CmbFileName1 = SameAsTable(CmbFieldName1.Text.Trim)
Queryinfo.CmbFileName2 = SameAsTable(CmbFieldName2.Text.Trim)
Queryinfo.CmbFileName3 = SameAsTable(CmbFieldName3.Text.Trim)
Queryinfo.CmbRelation1 = SameAsTable(CmbRelation1.Text.Trim)
Queryinfo.CmbRelation2 = SameAsTable(CmbRelation2.Text.Trim)
Queryinfo.TxtMessage1 = TxtMessage1.Text.Trim
Queryinfo.TxtMessage2 = TxtMessage2.Text.Trim
Queryinfo.TxtMessage3 = TxtMessage3.Text.Trim

Try
Dim facade As New Facade.Facade
Dim table As DataTable
table = facade.PowerQuery(Queryinfo)

If table.Rows.Count = 0 Then
MsgBox("没有查到任何记录")
Else
DataGridView1.DataSource = table
End If

Catch ex As Exception
MsgBox("查询过程出错了")
End Try

End Sub

''' <summary>
''' 虚方法 使得表中填写的字段名与数据库中保持一致
''' </summary>
''' <param name="cmbFileName"></param>
''' <returns></returns>
''' <remarks></remarks>
Protected Overridable Function SameAsTable(cmbFileName As String) As String
Return ""
End Function

''' <summary>
'''
''' 虚方法 获得数据库的名字
''' </summary>
''' <returns></returns>
''' <remarks></remarks>
Protected Overridable Function getDTName() As String
Return ""
End Function

Private Sub BtnExit_Click(sender As Object, e As EventArgs) Handles BtnExit.Click
Me.Close()
FrmMain.Show()
End Sub

Private Sub FrmPowerQuery_Load(sender As Object, e As EventArgs) Handles MyBase.Load
'combo框只能从下拉菜单里面选择不可以输入
CmbActor1.DropDownStyle = 2
CmbActor2.DropDownStyle = 2
CmbActor3.DropDownStyle = 2
CmbFieldName1.DropDownStyle = 2
CmbFieldName2.DropDownStyle = 2
CmbFieldName3.DropDownStyle = 2
CmbRelation1.DropDownStyle = 2
CmbRelation2.DropDownStyle = 2
End Sub
End Class

学生信息维护 U层代码：

Public Class FrmStudentInfoMaintain1
Private Sub FrmStudentInfoMaintain_Load(sender As Object, e As EventArgs) Handles MyBase.Load
CmbFieldName1.Items.Add("卡号")
CmbFieldName1.Items.Add("姓名")
CmbFieldName1.Items.Add("学号")
CmbFieldName1.Items.Add("性别")
CmbFieldName1.Items.Add("系别")
CmbFieldName1.Items.Add("年级")
CmbFieldName1.Items.Add("班级")

CmbFieldName2.Items.Add("卡号")
CmbFieldName2.Items.Add("姓名")
CmbFieldName2.Items.Add("学号")
CmbFieldName2.Items.Add("性别")
CmbFieldName2.Items.Add("系别")
CmbFieldName2.Items.Add("年级")
CmbFieldName2.Items.Add("班级")

CmbFieldName3.Items.Add("卡号")
CmbFieldName3.Items.Add("姓名")
CmbFieldName3.Items.Add("学号")
CmbFieldName3.Items.Add("性别")
CmbFieldName3.Items.Add("系别")
CmbFieldName3.Items.Add("年级")
CmbFieldName3.Items.Add("班级")
End Sub

Protected Overrides Function SameAsTable(cmbFileName As String) As String
Select Case cmbFileName
Case "卡号"
SameAsTable = "CardNO"
Case "姓名"
SameAsTable = "studentName"
Case "学号"
SameAsTable = "studentNO"
Case "性别"
SameAsTable = "Sex"
Case "系别"
SameAsTable = "Department"
Case "年级"
SameAsTable = "Grade"
Case "班级"
SameAsTable = "Class"
Case "与"
SameAsTable = "and"
Case "或"
SameAsTable = "or"
Case "<>"
SameAsTable = "<>"
Case "<"
SameAsTable = "<"
Case ">"
SameAsTable = ">"
Case "="
SameAsTable = "="
Case Else
SameAsTable = ""
End Select
End Function

Protected Overrides Function getDTName() As String
Return "Student"
End Function

End Class

连接数据库：三个功能中用的表不一样，所以在SQLHelper中添加一个方法，不直接传参，代码如下：

Public Function Query(ByVal cmdText As String, ByVal cmdType As CommandType) As DataTable
Dim sqlAdapter As SqlDataAdapter '定义数据适配器)
Dim dt As New DataTable
Dim ds As New DataSet

'给cmd赋值
cmd.CommandText = cmdText   'cmdtext为要执行的sql语句
cmd.CommandType = cmdType   '命令执行的类型
cmd.Connection = conn

sqlAdapter = New SqlDataAdapter(cmd) '实例化Adapter
Try
sqlAdapter.Fill(ds) '用adapter将dataset填充
dt = ds.Tables(0) 'datatable为dataSet的第一个表

Catch ex As Exception
MsgBox("数据库操作失败")
Finally
Call CloseCmd(cmd) '销毁cmd命令
End Try
Return dt
End Function

D层：

Public Function PowerQuery(ByVal Queryinfo As Entity.ePowerQueryEntity) As DataTable Implements IPowerQuery.PowerQuery
Dim sqlinfo As String '用于存放sql语句
Dim table As DataTable
Dim sqlhelper As New SQLHelper.sqlHelper
Dim cmdtype As CommandType = New CommandType()

If Queryinfo.CmbRelation1 = "" Then
sqlinfo = "Select * from " & Queryinfo.DBName & " where" & Chr(32) & Queryinfo.CmbFileName1 & Queryinfo.CmbActor1 & "'" & Queryinfo.TxtMessage1 & "'"
'@FileName1 @Actor1 @Message1"
ElseIf Queryinfo.CmbRelation1 <> "" And Queryinfo.CmbRelation2 = "" Then
sqlinfo = "select * from" & Chr(32) & Queryinfo.DBName & Chr(32) & "where" & Chr(32) & Queryinfo.CmbFileName1 & Chr(32) & Queryinfo.CmbActor1 & Chr(32) & "'" & Queryinfo.TxtMessage1 & "'" & Chr(32) & Queryinfo.CmbRelation1 & Chr(32) & Queryinfo.CmbFileName2 & Chr(32) & Queryinfo.CmbActor2 & Chr(32) & "'" & Queryinfo.TxtMessage2 & "'"
Else
sqlinfo = "select * from" & Chr(32) & Queryinfo.DBName & Chr(32) & "where" & Chr(32) & Queryinfo.CmbFileName1 & Chr(32) & Queryinfo.CmbActor1 & Chr(32) & "'" & Queryinfo.TxtMessage1 & "'" & Chr(32) & Queryinfo.CmbRelation1 & Chr(32) & Queryinfo.CmbFileName2 & Chr(32) & Queryinfo.CmbActor2 & Chr(32) & "'" & Queryinfo.TxtMessage2 & "'" & Chr(32) & Queryinfo.CmbRelation2 & Chr(32) & Queryinfo.CmbFileName3 & Chr(32) & Queryinfo.CmbActor3 & Chr(32) & "'" & Queryinfo.TxtMessage3 & "'"
End If
table = sqlhelper.Query(sqlinfo, CommandType.Text)
Return table
End Function

做完组合查询三个功能以后，感觉设计模式确实很神奇，简洁方便。自己写的代码还是有很多重复的地方，有很多漏洞，看别人的博客学到很多方法，开始觉得很难，做完了也就不觉得了，不要被自己吓倒，慢慢积累。