VB.NET & (三层+泛型)实现组合查询

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对于组合查询,真的是“费劲苦难”,当然也只是玩笑话,下边谈谈自己拼接字符串的办法吧!当然对于泛型集合的学习,详情《泛型集合,解决Datatable强耦合

首先我们要明确声明一个实体层,定义组合查询为实体类,将"字段,操作符,组合关系分别设为实体类combinQuery的属性

 '字段1
    Private _ComboFileName1 As String
    Public Property ComboFileName1() As String
        Get
            Return _ComboFileName1
        End Get
        Set(value As String)
            _ComboFileName1 = value
        End Set
    End Property
    '字段2
    Private _ComboFileName2 As String
    Public Property ComboFileName2() As String
        Get
            Return _ComboFileName2
        End Get
        Set(value As String)
            _ComboFileName2 = value
        End Set
    End Property
…………
对于U层,我们除了要实现参数赋值,还要将其记录显示在DataGridView中,在显示的这一阶段自己采用了泛型集合,将datatable类型转换成了集合而显示出来

看U层:

Private Sub btnQuery_Click(sender As Object,e As EventArgs) Handles btnQuery.Click
        'combinQuery_m  ,定义一个实体
        Dim combinQuery_m As IList(Of Entity.RegisterEntity)   '定义泛型集合
        Dim combinQuery_bll As New BLL.StusInfoMainBLL    '定义一个B层接口
        Dim combinQuery As New Entity.CombinQueryEntity    '定义一个实体,作为参数

        Dim table As String = "T_student"    '用到的表,与学生表联系起来

        Dim arrayControl(2) As Control
 '给参数赋值  
        With combinQuery
            '将查询条件字段1的值赋给实体combinQuery_m的字段1ComboFileName1属性  
            .ComboFileName1 = ComboFileName1.Text.Trim()
            .ComboFileName2 = ComboFileName2.Text.Trim()
            .ComboFileName3 = ComboFileName3.Text.Trim()
            ''将操作符1的值赋给实体combinQuery_m的操作符1ComboSign1属性  
            .ComboSign1 = ComboSign1.Text.Trim()
            .ComboSign2 = ComboSign2.Text.Trim()
            .ComboSign3 = ComboSign3.Text.Trim()
            '将查询内容1的值赋给实体combinQuery_m的查询内容1txtInqure1属性  
            .txtInqure1 = txtInqure1.Text.Trim()
            .txtInqure2 = txtInqure2.Text.Trim()
            .txtInqure3 = txtInqure3.Text.Trim()
            '将组合关系1的值赋给实体combinQuery_m的组合关系1ComboRelation1属性 
            .ComboRelation1 = ComboRelation1.Text.Trim()
            .ComboRelation2 = ComboRelation2.Text.Trim()
        End With
combinQuery_m = combinQuery_bll.StusInfo(table,combinQuery)


        DataGridView1.DataSource = combinQuery_m   '查询到的集合
以上代码主要还是实现将查询到的集合反馈到DataGridView的过程
我们还要将字符串转化,给字段,操作符,组合关系等分别赋值

查询字段(1,2,3)对应于”表“的字段(eg: cardNo),操作符对应于关系运算符,组合关系对应于逻辑运算符(or/and)

看部分代码

'字符串转换
        '给字段1赋值
        Select Case (combinQuery.ComboFileName1)
            Case "卡号"
                combinQuery.ComboFileName1 = "cardNo"
            Case "学号"
                combinQuery.ComboFileName1 = "studentNo"
            Case "姓名"
                combinQuery.ComboFileName1 = "studentName"
            Case "性别"
                combinQuery.ComboFileName1 = "sex"
            Case "年级"
                combinQuery.ComboFileName1 = "Grade"
            Case "班级"
                combinQuery.ComboFileName1 = "sclass"
        End Select
 '操作符1
        Select Case combinQuery.ComboSign1
            Case "="
                combinQuery.ComboSign1 = "="
            Case ">"
                combinQuery.ComboSign1 = ">"
            Case "<"
                combinQuery.ComboSign3 = "<"
            Case "<>"
                combinQuery.ComboSign1 = "<>"
        End Select
  '组合关系1
        Select Case combinQuery.ComboRelation1
            Case "或"
                combinQuery.ComboRelation1 = "or"
            Case "与"
                combinQuery.ComboRelation1 = "and"
        End Select
由于在整个系统过程中,我们涉及到了四个组合查询,所以定义了一个字符串类型的Table,实现了代码的复用性。以下则是拼接字符串的方法
 ''' <summary>
    ''' 生成组合查询sql语句-拼接sql字符串
    ''' </summary>
    ''' <param name="table"></param>
    ''' <param name="combinQuery">combinQuery实体</param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Function CombinsqlQuery(ByVal table As String,ByVal combinQuery As Entity.CombinQueryEntity) As String
        '首先,第一个查询条件有效  

        Dim sql As String = "select * from " & table & " where  " & combinQuery.ComboFileName1 & " " & combinQuery.ComboSign1 & " " & combinQuery.txtInqure1.Trim()
        If combinQuery.ComboRelation1 = "" Then    '如果第一个组合关系为空,则第一个查询条件有效  
            Return sql

        Else     '如果第一个组合关系不为空,则前两个查询条件有效  
            sql = sql & " " & combinQuery.ComboRelation1 & " " & combinQuery.ComboFileName2 & " " & combinQuery.ComboSign2 & " " & combinQuery.txtInqure2.Trim()

            If combinQuery.ComboRelation2 = "" Then     '如果第一个组合关系不为空,第二个组合关系为空,则仅仅前两个查询条件有效  
                Return sql
            Else       '如果第一二组合关系不为空,则三个查询条件均有效  
                sql = sql & " " & combinQuery.ComboRelation2 & " " & combinQuery.ComboFileName3 & " " & combinQuery.ComboSign3 & " " & combinQuery.txtInqure3.Trim()

                Return sql
            End If

        End If

        If combinQuery.ComboRelation1 <> "" And combinQuery.ComboRelation2 = "" Then     '如果第一个组合关系不为空,第二个组合关系为空,则前两个查询条件有效  
            sql = sql & " " & combinQuery.ComboRelation1 & " " & combinQuery.ComboFileName2 & " " & combinQuery.ComboSign2 & " " & combinQuery.txtInqure2.Trim()

        ElseIf combinQuery.ComboRelation1 <> "" And combinQuery.ComboRelation2 <> "" Then '如果第一个组合关系和第二个组合关系均不为空,则三个查询条件有效  
            sql = sql

        End If
    End Function
由于是D层实现调用,所以我把这个过程以一个Module形式定义在了D层中,下边看最关键的D层部分:
Private clssqlhelper As DAL.sqlhelper = New DAL.sqlhelper()   '声明并实例化
    ''' <summary>
    ''' 泛型集合,组合查询
    ''' </summary>
    ''' <param name="table"></param>
    ''' <param name="combinQuery"></param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Function StuInfoQuery(ByVal table As String,ByVal combinQuery As Entity.CombinQueryEntity) As <span style="color:#3333ff;">IList(Of Entity.RegisterEntity</span>) Implements IDAL.IStusInfoMainDAL.StuInfoQuery

        Dim dt As New DataTable
        Dim myList As IList(Of Entity.RegisterEntity)     '保存转化后的泛型集
        '调用查询语句
        'sql语句。调用Model层combinQuery类的方法CombinQuerysql()方法,返回sql语句  
        Dim strsql As String = CombinQueryModule.CombinsqlQuery(table,combinQuery)
        dt = clssqlhelper.Query(strsql,CommandType.Text)    '执行查询

        '将dt转换为泛型集合
       myList = EntityHelper.converToList(Of RegisterEntity)(dt)
        Return myList
    End Function
整个过程自己尝试定义了工厂类和接口,所以B层直接声明了一个变量,调用由Factory的方法返回来的接口
  '声明并实例化Factory为DataAccess类
    Private ReadOnly factory As DataAccess = New DataAccess
    Public Function StusInfo(ByVal data As String,ByVal StusQuery As Entity.CombinQueryEntity) As IList(Of Entity.RegisterEntity)
        '声明并实例化变量InterfaceUser为:调用Factory.CreateUserDAL()所返回来的IUser
        Dim comboQuery As IStusInfoMainDAL = factory.StusInfoMain()
        Dim StusMain As IList(Of Entity.RegisterEntity)   '定义一个泛型集合
        StusMain = comboQuery.StuInfoQuery(data,StusQuery)</span>

        Return StusMain
    End Function
这样组合查询的整个过程就完成了,整个过程的实现,很好的遵守了三层架构的要求,实现了解耦的目的。当然除了拼接字符串还有使用存储过程实现的方法,这样就无需大量赋值,而且也就不用拼接字符串了,直接将这些全部定义在了存储过程中,然后再存储过程中直接传入参数就好了,虽然自己明白整个过程的实现,但是还是欠缺实践,希望在合作开发的过程中能够熟练对于各种技巧的使用。 原文链接:https://www.f2er.com/vb/257884.html

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