VB.NET版机房收费系统---组合查询

查询的意思就是查找，寻找，指在某一个或几个地方找出自己所要的信息，假如我想搜索一下我自己写的博客，名字叫做初雪之恋，我在百度的搜索框中输入丁国华三个字，会有怎样的惊喜等着我？

啊哦，这个信息并不是我想要的，于是我再搜，“丁国华廊坊师范学院 csdn”搜索结果如下：

很显然，这个还不是我想要的结果，我接着搜，“丁国华廊坊师范学院 csdn 初雪之恋”；

在我的理解中，组合查询就是通过条件层层限制，一步一步精确，得到我们想要的答案，在机房收费系统中，有好几处涉及组合查询，接下来，以学生基本信息维护为例，讲解组合查询。在第二次机房收费系统中，我没有按原来胡阳版的模板来，原版的通过卡号，学号，姓名，性别，系别，年级，班号七个字段，来进行查询，操作符分别为等于，大于，小于，不等于，可是，现实生活中哪有性别大于什么，姓名小于什么的条件，所以我重新设计了一下窗体，从中挑选了四个字段名作为组合查询的条件简化了组合查询的难度，主界面设计如下：

接下来，看看我们的具体实现过程，首先实体层---E层；

<span style="font-size:18px;">Public Class StudentinfoPublic studentNo As String                      '字段Public Property _studentNo As String            '属性GetReturn studentNoEnd GetSet(value As String)studentNo = valueEnd SetEnd PropertyPublic cardNo As StringPublic Property _cardNo As StringGetReturn cardNoEnd GetSet(value As String)cardNo = valueEnd SetEnd PropertyPublic studentName As StringPublic Property _studentName As StringGetReturn studentNameEnd GetSet(value As String)studentName = valueEnd SetEnd PropertyPublic sex As StringPublic Property _sex As StringGetReturn sexEnd GetSet(value As String)sex = valueEnd SetEnd PropertyPublic department As StringPublic Property _departmentGetReturn departmentEnd GetSet(value)department = valueEnd SetEnd PropertyPublic grade As StringPublic Property _gradeGetReturn gradeEnd GetSet(value)grade = valueEnd SetEnd PropertyPublic stuclass As StringPublic Property _stuclassGetReturn stuclassEnd GetSet(value)stuclass = valueEnd SetEnd PropertyPublic remark As StringPublic Property _remarkGetReturn remarkEnd GetSet(value)remark = valueEnd SetEnd PropertyPublic Handler As StringPublic Property _HandlerGetReturn HandlerEnd GetSet(value)Handler = valueEnd SetEnd Property
End Class
</span>

数据访问层---D层

<span style="font-size:18px;">Imports System.Data.SqlClient
Public Class StuBaInforPreserveDAOPublic Function query(ByVal cmbOperator1 As String, ByVal cardNo As String, ByVal cmbOperator2 As String, ByVal studentNo As String, ByVal cmbOperator3 As String, ByVal department As String, ByVal cmbOperator4 As String, ByVal grade As String) As DataTableDim db As New Entity.Dbutil '实例化数据库连接Dim dt As New DataTable       '实例化DataTableUsing conn As New SqlConnection(db.connstring)conn.Open()                       '打开数据库连接Dim sql As StringDim cmd As SqlCommandDim dataAdpter As New SqlDataAdapterDim dst As New DataSetDim flag(3) As Boolean             ’定义标签sql = "select studentNo,cardNo,studentName,sex,department,grade,class,remark,handler  from Student_info where "If Not (cardNo = "") Then                                   '如果卡号不为空，执行下面这句sql语句sql = sql & "studentNo" & cmbOperator1 & "'" & cardNo & "'"flag(0) = TrueEnd IfIf Not (studentNo = "") Then     '如果学号不为空，且卡号不为空，执行第一个sql语句，如果学号不为空，卡号为空执行第二个sql语句flag(1) = TrueIf flag(0) = True Thensql = sql & "and studentNo " & cmbOperator2 & "'" & studentNo & "'"Elsesql = sql & "studentNo" & cmbOperator2 & "'" & studentNo & "'"End IfEnd IfIf Not (department = "") Then '如果系别不为空，且学号和卡号中有一个被选择，或者两个都选，执行第一个sql语句，否则执行第二个sql语句flag(2) = TrueIf flag(0) = True Or flag(1) = True Thensql = sql & "and department " & cmbOperator3 & "'" & department & "'"Elsesql = sql & "department" & cmbOperator3 & "'" & department & "'"End IfEnd IfIf Not (grade = "") Then      '如果年级不为空，且学号，卡号，系别中有一个被选择，或者一个or两个被选择执行第一个sql语句，否则执行第二句flag(3) = TrueIf flag(0) = True Or flag(1) = True Or flag(2) = True Thensql = sql & "and grade" & cmbOperator4 & "'" & grade & "'"Elsesql = sql & "grade" & cmbOperator4 & "'" & grade & "'"End IfEnd Ifcmd = New SqlCommand(sql, conn)dataAdpter.SelectCommand = cmddataAdpter.Fill(dst, "Student_info")dt = dst.Tables("Student_info")End UsingReturn dtEnd Function
End Class
</span>

业务逻辑层---B层；

<span style="font-size:18px;">Public Class StuBaInforPreserveManagerPublic Function query(ByVal cmbOperator1 As String, ByVal cardNo As String, ByVal cmbOperator2 As String, ByVal studentNo As String, ByVal cmbOperator3 As String, ByVal department As String, ByVal cmbOperator4 As String, ByVal grade As String) As DataTableDim StuBaInforPreserveDAO As New DAL.StuBaInforPreserveDAO                 '调用D层Return StuBaInforPreserveDAO.query(cmbOperator1, cardNo, cmbOperator2, studentNo, cmbOperator3, department, cmbOperator4, grade)End Function
End Class</span>

显示层---U层；

<span style="font-size:18px;">Imports BLLPublic Class frmStuBaInforPreservePrivate Sub btnInquery_Click(sender As Object, e As EventArgs) Handles btnInquery.ClickDim StuBaInforPreserveManager As New BLL.StuBaInforPreserveManager  '调用B层Dim dt As New DataTabledt = StuBaInforPreserveManager.query(cmbOperator1.Text, txtCardNo.Text, cmbOperator2.Text, txtStuNo.Text, cmbOperator3.Text, txtDepartment.Text, cmbOperator4.Text, txtGrade.Text)DataGridView1.AutoGenerateColumns = True  '自动创建列DataGridView1.DataSource = dtDataGridView1.Columns(0).HeaderText = "学号"         '把相关信息在datagridview中显示出来DataGridView1.Columns(1).HeaderText = "卡号"DataGridView1.Columns(2).HeaderText = "姓名"DataGridView1.Columns(3).HeaderText = "性别"DataGridView1.Columns(4).HeaderText = "系别"DataGridView1.Columns(5).HeaderText = "年级"DataGridView1.Columns(6).HeaderText = "班级"DataGridView1.Columns(7).HeaderText = "备注"End SubPrivate Sub frmStuBaInforPreserve_Load(sender As Object, e As EventArgs) Handles MyBase.LoadcmbOperator1.Enabled = False             '窗体加载时，需要注意的一些细节问题，比如那些按钮能点，那些不能点txtCardNo.Text = ""txtCardNo.Enabled = FalsecmbOperator1.Items.Add("=")cmbOperator1.Items.Add(">")cmbOperator1.Items.Add("<")cmbOperator1.Items.Add("<>")cmbOperator1.SelectedIndex = 0cmbOperator2.Enabled = FalsetxtStuNo.Text = ""txtStuNo.Enabled = FalsecmbOperator2.Items.Add("=")cmbOperator2.Items.Add(">")cmbOperator2.Items.Add("<")cmbOperator2.Items.Add("<>")cmbOperator2.SelectedIndex = 0cmbOperator3.Enabled = FalsetxtDepartment.Text = ""txtDepartment.Enabled = FalsecmbOperator3.Items.Add("=")cmbOperator3.Items.Add("<>")cmbOperator3.SelectedIndex = 0cmbOperator4.Enabled = FalsetxtGrade.Text = ""txtGrade.Enabled = FalsecmbOperator4.Items.Add("=")cmbOperator4.Items.Add("<>")cmbOperator4.SelectedIndex = 0End SubPrivate Sub btnExit_Click(sender As Object, e As EventArgs) Handles btnExit.Click        '退出按钮Me.Close()End SubPrivate Sub chkCardNo_Click(sender As Object, e As EventArgs) Handles chkCardNo.Click  '如果卡号被选中，则txtCardNo和cmbOperator1可以点否者不能点，并且文本框的内容自动情况，恢复默认值If chkCardNo.Checked ThentxtCardNo.Enabled = TruecmbOperator1.Enabled = TrueElsetxtCardNo.Enabled = FalsecmbOperator1.Enabled = FalsetxtCardNo.Text = ""cmbOperator1.SelectedIndex = 0End IfEnd SubPrivate Sub chkStuNo_Click(sender As Object, e As EventArgs) Handles chkStuNo.ClickIf chkStuNo.Checked ThentxtStuNo.Enabled = TruecmbOperator2.Enabled = TrueElsetxtStuNo.Enabled = FalsecmbOperator2.Enabled = FalsetxtStuNo.Text = ""cmbOperator2.SelectedIndex = 0End IfEnd SubPrivate Sub chkDepartment_Click(sender As Object, e As EventArgs) Handles chkDepartment.ClickIf chkDepartment.Checked ThentxtDepartment.Enabled = TruecmbOperator3.Enabled = TrueElsetxtDepartment.Enabled = FalsecmbOperator3.Enabled = FalsetxtDepartment.Text = ""cmbOperator3.SelectedIndex = 0End IfEnd SubPrivate Sub chkGrade_Click(sender As Object, e As EventArgs) Handles chkGrade.ClickIf chkGrade.Checked ThentxtGrade.Enabled = TruecmbOperator4.Enabled = TrueElsetxtGrade.Enabled = FalsecmbOperator4.Enabled = FalsetxtGrade.Text = ""cmbOperator4.SelectedIndex = 0End IfEnd Sub
End Class</span>

运行效果如下：

自此学生基本信息维护就暂时告一段落，开始敲学生基本信息维护的时候，不知道从哪儿下手，各种纠结，各种逃避，各种不想敲，可是，我已经长大了，我不能再由着我自己的性子来做事，我要为我自己做的事情负责任，走过去了，真的有那么困难么？我想其中的滋味只有走过的人才能够真正明白。

曾经看到米老师给一篇博文这样的评语，这篇博客的主要内容，我记不清楚了，好像是解决一个问题，然后成功解决的一篇博文，米老师说，这个过程是不是很养人，对，这个过程不光养人，而且锻炼人，考验我们面对新知识的心态，是一拖再拖，今目标红了又红，还是坦然面对，两天把三个组合查询一一搞定，机房收费系统未完，待续......

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