组合查询(vb.net+三层架构之机房收费系统)

在机房收费系统中有三个窗体功能涉及到组合查询。vb版的组合查询和.net+三层架构版的组合查询还是有一些区别的。虽然有区别，但是，核心不变——拼接字符串。

为什么说组合查询是一个小难点？

1,它与普通查询的区别:普通查询只要一条含有参数的sql语句即可.例如根据卡号查余额(其中@CardID为参数).Dim sql As String = "selectCardID,StudentInfo.StuID,StuName,Sex,Department,Grade,Class,Explian,Cash,CardInfo.Status from StudentInfo,CardInfo where StudentInfo.StuID=CardInfo.StuID And CardInfo.CardID=@CardIDand CardInfo.Status='使用'"

(1)可以说参数@CardID的值是确定的，直接将txtCardID中的内容传递过来即可。而组合查询的参数不止一个，并且是动态的,选择不同的查询条件，就会有不同的参数，并且查询条件不止一个。

(2)并且(普通的查询（按上例）操作符为“=”，而组合查询操作符不确定（=、>、<、<>）;

(3)普通查询只有一个查询条件，组合查询有多条，并且关系不确定（或、与）

2,两层的组合查询和三层的组合查询又不一样？

原因：三层的sql语句需要参数传递，两层无需参数，直接在本层完成

我的设计:1,没有点击第一个组合关系的话,后两排控件不可用.即,只有第一个查询条件有效;2,点击了第一个组合关系,但是组合关系框内没有选内容,即便后两排填了查询条件也无效;3,并且选择了其中一种关系(或/与)，如果第二排没有填写查询条件或条件输入不完整则会提示“请将查询条件输入完整！”，此时前两个查询条件输入有效；4，第二个组合关系，同理。

看起来很复杂，其实就是：选择的组合关系框数，决定有效的查询条件数。条件输入不完整时，提示。

我还增加了修改信息功能，有意者可以私下讨论。

看代码:

设计到的View_StuInfo视图：

UI层:

????Public Class FrmManageStuInfo
    '点击“查询”按钮
    Private Sub btCheck_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles btCheck.Click
        Dim combinQuery_m As New Model.combinQuery
        Dim combinQuery_bll As New BLL.combinQuery_BLL
        Dim ds As DataSet
        Dim table As String = "View_StuInfo"    '视图View_StuInfo

        Dim arrayCtr(8) As Control    '定义控件数组

        '给数组赋值
        arrayCtr(0) = cmbField1   '字段1控件
        arrayCtr(1) = cmbField2   '字段2控件
        arrayCtr(2) = cmbField3   '字段3控件

        arrayCtr(3) = cmbOperate1  '操作符1控件
        arrayCtr(4) = cmbOperate2   '操作符2控件
        arrayCtr(5) = cmbOperate3   '操作符3控件

        arrayCtr(6) = txtContent1   '查询内容1控件
        arrayCtr(7) = txtContent2    '查询内容2控件
        arrayCtr(8) = txtContent3    '查询内容3控件

        '当组合关系1=空，并且组合关系2不可用；或者组合关系1！=空，并且组合关系2不可用时
        If (cmbAndOr1.Text = "" And cmbAndOr2.Enabled = False) Or (Not cmbAndOr1.Text = "" And cmbAndOr2.Enabled = True) Then

            '调用UI层combinQuery_UI类中的TxtIsNull()方法，判断除两个组合关系控件外的所有可用控件是否为空
            If combinQuery_UI.TxtIsNull(arrayCtr) Then       '除两个组合关系控件外，如果存在内容为空的控件，则提示“请将查询条件输入完整”

                MessageBox.Show("请将查询条件输入完整！")
                Exit Sub

            End If

        End If


        '给参数赋值
        combinQuery_m.CmbField1 = cmbField1.Text.Trim()    '将查询条件字段1的值赋给实体combinQuery_m的字段1CmbField1属性
        combinQuery_m.CmbField2 = cmbField2.Text.Trim()    '将查询条件字段2的值赋给实体combinQuery_m的字段2CmbField2属性
        combinQuery_m.CmbField3 = cmbField3.Text.Trim()    '将查询条件字段3的值赋给实体combinQuery_m的字段3CmbField3属性

        combinQuery_m.CmbOperate1 = cmbOperate1.Text.Trim() '将操作符1的值赋给实体combinQuery_m的操作符1CmbOperate1属性
        combinQuery_m.CmbOperate2 = cmbOperate2.Text.Trim() '将操作符2的值赋给实体combinQuery_m的操作符2CmbOperate2属性
        combinQuery_m.CmbOperate3 = cmbOperate3.Text.Trim() '将操作符3的值赋给实体combinQuery_m的操作符3CmbOperate3属性

        combinQuery_m.TxtContent1 = txtContent1.Text.Trim()  '将查询内容1的值赋给实体combinQuery_m的查询内容1TxtContent1属性
        combinQuery_m.TxtContent2 = txtContent2.Text.Trim()  '将查询内容2的值赋给实体combinQuery_m的查询内容2TxtContent2属性
        combinQuery_m.TxtContent3 = txtContent3.Text.Trim()  '将查询内容3的值赋给实体combinQuery_m的查询内容3TxtContent3属性

        combinQuery_m.CmbAndOr1 = cmbAndOr1.Text.Trim()   '将组合关系1的值赋给实体combinQuery_m的组合关系1CmbAndOr1属性
        combinQuery_m.CmbAndOr2 = cmbAndOr2.Text.Trim()   '将组合关系2的值赋给实体combinQuery_m的组合关系2CmbAndOr2属性


        '调用Model层combinQuery类的StudentInfoField()方法，返回界面中每个查询字段中对应的表中的每个字段名，以实体形式保存
        combinQuery_m = Model.combinQuery.StudentInfoField(combinQuery_m)

        '调用BLL层CombinQuery_BLL()方法，返回数据集ds
        ds = combinQuery_bll.CombinQuery_BLL(table,combinQuery_m)

        'DataGridView1控件绑定数据源
        DataGridView1.DataSource = ds.Tables("NewTable")

        DataGridView1.Columns(0).HeaderText = "学号"
        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 = "金额"
        DataGridView1.Columns(8).HeaderText = "状态"
        DataGridView1.Columns(9).HeaderText = "备注"

        'DataGridView1控件的列绑定数据表中的列
        For i = 0 To ds.Tables("NewTable").Rows.Count - 1
            DataGridView1.Columns(i).DataPropertyName = ds.Tables("NewTable").Columns(i).ToString()

        Next i

        btModify.Enabled = True

    End Sub
    '点击“组合关系1”控件
    Private Sub cmbAndOr1_Click(ByVal sender As Object,ByVal e As System.EventArgs) Handles cmbAndOr1.Click
        '输入第二个条件的控件们可用
        cmbField2.Enabled = True
        cmbOperate2.Enabled = True
        txtContent2.Enabled = True
        cmbAndOr2.Enabled = True

    End Sub
  
    '  窗体加载
    Private Sub FrmManageStuInfo_Load(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles MyBase.Load

        '窗体加载时，将DataGridView控件设为只读的，即，不可编辑。只有当点击“修改”按钮时，才可编辑，将ReadOnly=False
        DataGridView1.ReadOnly = True

        '“修改”按钮和“保存修改”按钮不可用。当 点击“查询”按钮，并且有查询内容（查询内容不为空）时，“修改”按钮才可用
        btModify.Enabled = False
        btSaveModify.Enabled = False

        '输入第二个条件的控件们不可用
        cmbField2.Enabled = False
        cmbOperate2.Enabled = False
        txtContent2.Enabled = False
        cmbAndOr2.Enabled = False

        '输入第三个条件的控件们不可用
        cmbField3.Enabled = False
        cmbOperate3.Enabled = False
        txtContent3.Enabled = False

    End Sub

    '选择“组合关系1”中值时
    Private Sub cmbAndOr1_SelectedIndexChanged(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles cmbAndOr1.SelectedIndexChanged

        '输入第二个条件的控件们可用
        cmbField2.Enabled = True
        cmbOperate2.Enabled = True
        txtContent2.Enabled = True
        cmbAndOr2.Enabled = True

    End Sub
    '选择“组合关系2”中值时
    Private Sub cmbAndOr2_SelectedIndexChanged(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles cmbAndOr2.SelectedIndexChanged

        '输入第三个条件的控件们可用
        cmbField3.Enabled = True
        cmbOperate3.Enabled = True
        txtContent3.Enabled = True

    End Sub

BLL层:

Public Class combinQuery_BLL
    ''' <summary>
    ''' 组合查询
    ''' </summary>
    ''' <param name="combinQuery"></param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Function CombinQuery_BLL(ByVal table As String,ByVal combinQuery As Model.combinQuery) As DataSet

        Dim combinQuery_da As New DAL.combinQuery_DA
        Dim ds As DataSet

        ds = combinQuery_da.CombinQuery_DA(table,combinQuery)

        Return ds

    End Function
End Class

DAL层:

'组合查询类
Public Class combinQuery_DA
    ''' <summary>
    ''' 组合查询
    ''' </summary>
    ''' <param name="table"></param>
    ''' <param name="combinQuery"></param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Function CombinQuery_DA(ByVal table As String,ByVal combinQuery As Model.combinQuery) As DataSet

        'sql语句。调用Model层combinQuery类的方法CombinQuerySql()方法，返回sql语句
        Dim sql As String = Model.combinQuery.CombinQuerySql(table,combinQuery)
        Dim ds As DataSet       '定义Dataset变量

        '调用ExecuteDataset()方法，返回数据集ds
        ds = New SqlHelper.SqlHelper().ExecuteDataSet(sql,CommandType.Text)

        Return ds

    End Function

实体层:

定义组合查询为实体类，并将“字段1”、“字段2”、”“字段3”、“操作符1”、“操作符2”、“操作符3”、“组合关系1”、“组合关系2” 设为实体类combinQuery的属性。

'组合查询信息类
Public Class combinQuery
    '字段1
    Private _cmbField1 As String
    Public Property CmbField1() As String
        Get
            Return _cmbField1
        End Get
        Set(ByVal value As String)
            _cmbField1 = value
        End Set
    End Property
    '字段2
    Private _cmbField2 As String
    Public Property CmbField2() As String
        Get
            Return _cmbField2
        End Get
        Set(ByVal value As String)
            _cmbField2 = value
        End Set
    End Property
    '字段3
    Private _cmbField3 As String
    Public Property CmbField3() As String
        Get
            Return _cmbField3
        End Get
        Set(ByVal value As String)
            _cmbField3 = value
        End Set
    End Property
    '操作符
    Private _cmbOperate1 As String
    Public Property CmbOperate1() As String
        Get
            Return _cmbOperate1
        End Get
        Set(ByVal value As String)
            _cmbOperate1 = value
        End Set
    End Property
    '操作符2
    Private _cmbOperate2 As String
    Public Property CmbOperate2() As String
        Get
            Return _cmbOperate2
        End Get
        Set(ByVal value As String)
            _cmbOperate2 = value
        End Set
    End Property
    '操作符3
    Private _cmbOperate3 As String
    Public Property CmbOperate3() As String
        Get
            Return _cmbOperate3
        End Get
        Set(ByVal value As String)
            _cmbOperate3 = value
        End Set
    End Property
    '查询内容1
    Private _txtContent1 As String
    Public Property TxtContent1() As String
        Get
            Return _txtContent1
        End Get
        Set(ByVal value As String)
            _txtContent1 = value
        End Set
    End Property
    '查询内容2
    Private _txtContent2 As String
    Public Property TxtContent2() As String
        Get
            Return _txtContent2
        End Get
        Set(ByVal value As String)
            _txtContent2 = value
        End Set
    End Property
    '查询内容3
    Private _txtContent3 As String
    Public Property TxtContent3() As String
        Get
            Return _txtContent3
        End Get
        Set(ByVal value As String)
            _txtContent3 = value
        End Set
    End Property
    '组合关系1
    Private _cmbAndOr1 As String
    Public Property CmbAndOr1() As String
        Get
            Return _cmbAndOr1
        End Get
        Set(ByVal value As String)
            _cmbAndOr1 = value
        End Set
    End Property
    '组合关系2
    Private _cmbAndOr2 As String
    Public Property CmbAndOr2() As String
        Get
            Return _cmbAndOr2
        End Get
        Set(ByVal value As String)
            _cmbAndOr2 = value
        End Set
    End Property

以下方法，用Select case语句给“字段1”、“字段2”、”“字段3”、“操作符1”、“操作符2”、“操作符3”、“组合关系1”、“组合关系2” 赋表的字段值。

  ''' <summary>
    ''' 将查询字段(例如:卡号)对应于StudentInfo表中的字段(例如:CardID)，将操作符对应于关系运算符,将组合关系(或/与)对应于逻辑运算符(Or/And)
    ''' </summary>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Shared Function StudentInfoField(ByVal combinQuery As combinQuery) As combinQuery

        'Dim combinQuery As New combinQuery   '实例化实体类combinQuery

        '查询字段1
        Select Case (combinQuery.CmbField1)
            Case "卡号"
                combinQuery.CmbField1 = "CardID"
            Case "学号"
                combinQuery.CmbField1 = "StuID"
            Case "姓名"
                combinQuery.CmbField1 = "StuName"
            Case "性别"
                combinQuery.CmbField1 = "Sex"
            Case "系别"
                combinQuery.CmbField1 = "Department"
            Case "年级"
                combinQuery.CmbField1 = "Grade"
            Case "班级"
                combinQuery.CmbField1 = "Class"
        End Select

        '查询字段2
        Select Case combinQuery.CmbField2
            Case "卡号"
                combinQuery.CmbField2 = "CardID"
            Case "学号"
                combinQuery.CmbField2 = "StuID"
            Case "姓名"
                combinQuery.CmbField2 = "StuName"
            Case "性别"
                combinQuery.CmbField2 = "Sex"
            Case "系别"
                combinQuery.CmbField2 = "Department"
            Case "年级"
                combinQuery.CmbField2 = "Grade"
            Case "班级"
                combinQuery.CmbField2 = "Class"
        End Select

        '查询字段3
        Select Case combinQuery.CmbField3
            Case "卡号"
                combinQuery.CmbField3 = "CardID"
            Case "学号"
                combinQuery.CmbField3 = "StuID"
            Case "姓名"
                combinQuery.CmbField3 = "StuName"
            Case "性别"
                combinQuery.CmbField3 = "Sex"
            Case "系别"
                combinQuery.CmbField3 = "Department"
            Case "年级"
                combinQuery.CmbField3 = "Grade"
            Case "班级"
                combinQuery.CmbField3 = "Class"
        End Select

        '操作符1
        Select Case combinQuery.CmbOperate1
            Case "="
                combinQuery.CmbOperate1 = "="
            Case ">"
                combinQuery.CmbOperate1 = ">"
            Case "<"
                combinQuery.CmbOperate1 = "<"
            Case "<>"
                combinQuery.CmbOperate1 = "<>"

        End Select

        '操作符2
        Select Case combinQuery.CmbOperate2
            Case "="
                combinQuery.CmbOperate2 = "="
            Case ">"
                combinQuery.CmbOperate2 = ">"
            Case "<"
                combinQuery.CmbOperate2 = "<"
            Case "<>"
                combinQuery.CmbOperate2 = "<>"

        End Select

        '操作符3
        Select Case combinQuery.CmbOperate3
            Case "="
                combinQuery.CmbOperate3 = "="
            Case ">"
                combinQuery.CmbOperate3 = ">"
            Case "<"
                combinQuery.CmbOperate3 = "<"
            Case "<>"
                combinQuery.CmbOperate3 = "<>"

        End Select

        '组合关系1
        Select Case combinQuery.CmbAndOr1
            Case "或"
                combinQuery.CmbAndOr1 = "Or"
            Case "与"
                combinQuery.CmbAndOr1 = "And"

        End Select

        '组合关系2
        Select Case combinQuery.CmbAndOr2
            Case "或"
                combinQuery.CmbAndOr2 = "Or"
            Case "与"
                combinQuery.CmbAndOr2 = "And"

        End Select

        Return combinQuery

    End Function

以下方法是拼接sql语句的方法。其中字符串类型的参数table的作用实现了代码复用性，因为不止在管理学生信息一个窗体是组合查询，还有查询教师工作记录,查询学生上机状态时也是组合查询. 通过table参数传递个窗体涉及到的表明,从而都可用次方法,代码复用.

 ''' <summary>
    ''' 生成组合查询sql语句——拼接sql字符串
    ''' </summary>
    ''' <param name="table">所需查询的表</param>
    ''' <param name="combinQuery">combinQuery实体</param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Shared Function CombinQuerySql(ByVal table As String,ByVal combinQuery As combinQuery) As String

        '首先，第一个查询条件有效
        Dim sql As String = "select * from " & table & " where " & combinQuery.CmbField1 & " " & combinQuery.CmbOperate1 & " " & combinQuery.TxtContent1
        If combinQuery.CmbAndOr1 = "" 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.CmbAndOr1 & " " & combinQuery.CmbField2 & " " & combinQuery.CmbOperate2 & " " & combinQuery.TxtContent2.Trim()

            If combinQuery.CmbAndOr2 = "" 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.CmbAndOr2 & " " & combinQuery.CmbField3 & " " & combinQuery.CmbOperate3 & " " & combinQuery.TxtContent3.Trim()

                Return sql
            End If

        End If

        If combinQuery.CmbAndOr1 <> "" And combinQuery.CmbAndOr2 = "" 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.CmbAndOr1 & " " & combinQuery.CmbField2 & " " & combinQuery.CmbOperate2 & " " & combinQuery.TxtContent2.Trim()

        ElseIf combinQuery.CmbAndOr1 <> "" And combinQuery.CmbAndOr2 <> "" 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

End Class

（编辑：李大同）

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