这几天一直在做机房收费系统中组合查询的那几个窗体。这次选择了利用数组来查询。下面就给大家说一下这个方法，希望大家指正，互相学习。

这里我要讲解的是在三层架构下实现的例子，如果你不了解三层，或者是没有听说过三层，那建议你在百度输入“三层 提高班.CSDN ”就可以看到有关三层的介绍。我们提高班的许多同学都对三层做了一些总结，对你学习、理解三层会有好处的。

言归正传，先看一下窗体的组成（U层）。

其中 ，3个“字段”下拉列表、3个“操作”下拉列表以及2个“组合关系”下拉列表中的条目分别相同。依次是“卡号、学号、姓名、性别”、“<、>、=、<>”、“与、或”。并且所要查询的记录在一个表中。

（注：下面代码只是为了讲解，对于命名规范等方面没有做考虑，望见谅。）

 Private Sub cmdOk_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles cmdOk.Click
        Select Case cbxName1.Text.Trim()
            Case "卡号"
                f1 = "CardNo"
            Case "学号"
                f1 = "SID"
            Case "姓名"
                f1 = "Name"
            Case "性别"
                f1 = "Sex"
        End Select

        Select Case cbxName2.Text
            Case ""              ‘此处很重要
                f2 = ""
            Case "卡号"
                f2 = "CardNo"
            Case "学号"
                f2 = "SID"
            Case "姓名"
                f2 = "Name"
            Case "性别"
                f2 = "Sex"
        End Select

        Select Case cbxName3.Text
            Case ""                ’此处很重要
                f3 = ""
            Case "卡号"
                f3 = "CardNo"
            Case "学号"
                f3= "SID"
            Case "姓名"
                f3 = "Name"
            Case "性别"
                f3 = "Sex"
        End Select

        Dim myarr As Entity.StudentE() = {New Entity.StudentE(),New Entity.StudentE(),New Entity.StudentE()}
        myarr(0).Name = f1
        myarr(1).Name = f2
        myarr(2).Name = f3

        Dim myarr1() As Entity.StudentE = {New Entity.StudentE,New Entity.StudentE,New Entity.StudentE}
        myarr1(0).Operation = cbxOperation1.Text
        myarr1(1).Operation = cbxOperation2.Text
        myarr1(2).Operation = cbxOperation3.Text

        Dim myarr2() As Entity.StudentE = {New Entity.StudentE,New Entity.StudentE}
        myarr2(0).txtName = txtName1.Text
        myarr2(1).txtName = txtName2.Text
        myarr2(2).txtName = txtName3.Text

        Dim e0 As String = ""
        Dim e1 As String = ""
        Select Case cbxCompone1.Text
            Case ""           ‘此处表示查询时只需要按照前三个条件进行查询
                e0 = ""
            Case "与"
                e0 = "and"
            Case "或"
                e0 = "or"
        End Select

        Select Case cbxCompone2.Text
            Case ""
                e1 = ""
            Case "与"
                e1 = "and"
            Case "或"
                e1 = "or"
        End Select

        Dim myarr3() As Entity.StudentE = {New Entity.StudentE,New Entity.StudentE}
        myarr3(0).Compone = e0
        myarr3(1).Compone = e1

        Dim mybll As New BLL.StudentBLL
        Dim dt As New DataTable
        dt = mybll.ShowSinfoCom(myarr,myarr1,myarr2,myarr3)
        If dt.Rows.Count() > 0 Then
            DataGridView1.DataSource = dt
        Else
            MessageBox.Show("没有记录")
        End If
    End Sub

其中，f1、f2、f3是全局变量。另外，对于其他的一些判断，例如当第一个“组合关系”为空的时候，后面的下拉列表和文本框等都不能允许操作等要求，在此并没有进行设置。

下面再来看看业务逻辑层（B层）

Function ShowSinfoCom(ByVal myarr() As Entity.StudentE,ByVal myarr1() As Entity.StudentE,ByVal myarr2() As Entity.StudentE,ByVal myarr3() As Entity.StudentE) As DataTable
        Dim mydal As New DAL.StudentDAL
        Dim dt As New DataTable
        dt = mydal.GetOnLineCom(myarr,myarr3)
        Return dt
    End Function

Function GetOnLineCom(ByVal myarr() As Entity.StudentE,ByVal myarr3() As Entity.StudentE) As DataTable


        Dim sql As String = "select * from Student_Info where " & myarr(0).Name & myarr1(0).Operation & " " & myarr2(0).txtName & myarr3(0).Compone & " " & myarr(1).Name & myarr1(1).Operation & " " & myarr2(1).txtName & myarr3(1).Compone & " " & myarr(2).Name & myarr1(2).Operation & myarr2(2).txtName & ""
        
        Return myDataTable
    End Function