在VB.NET 机房收费系统的组合查询中我写了完了一条线，然后看了其他同学对于组合查询的代码我感觉自己的代码很幼稚，不过还是想发表一下这个代码花了我半天的时间完成的。接下来就贴上图和代码。
组合查询的窗体：
U层代码：
Public ClassUIFrmOperatorWorkRecord
Private SubUIFrmOperatorWorkRecord_Load(ByVal sender As System.Object, ByVal e AsSystem.EventArgs) Handles MyBase.Load
’定义字符串数组
DimstrFieldName(6) As String
Dim strOperator(3) As String
Dim strCompositionRelation(1) As String
DimIntTemp As Integer
'给字符串数组赋值
For IntTemp = 0 To 6
Select Case IntTemp
Case 0
strFieldName(0) ="教师"
strOperator(0) ="="
strCompositionRelation(0) ="或"
Case 1
strFieldName(1) ="级别"
strOperator(1) =">"
strCompositionRelation(1) ="与"
Case 2
strFieldName(2) ="登录日期"
strOperator(2) ="<"
Case 3
strFieldName(3) ="登录时间"
strOperator(3) ="="
Case 4
strFieldName(4) ="注销日期"
Case 5
strFieldName(5) ="注销时间"
Case 6
strFieldName(6) ="机器名"
End Select
Next IntTemp
'控件增加字段
cboFieldName1.Items.AddRange(strFieldName)
cboFieldName2.Items.AddRange(strFieldName)
cboFieldName3.Items.AddRange(strFieldName)
cboOperator1.Items.AddRange(strOperator)
cboOperator2.Items.AddRange(strOperator)
cboOperator3.Items.AddRange(strOperator)
cboCompositionRelation1.Items.AddRange(strCompositionRelation)
cboCompositionRelation2.Items.AddRange(strCompositionRelation)
End Sub
Private Sub BtnCheck_Click(ByVal sender AsSystem.Object, ByVal e As System.EventArgs) Handles BtnCheck.Click
Dim ECombination As NewEntity.Combination
Dim BCombination As NewBLL.BLLOperatorWorkRecord
Dim dt As New DataTable
'把信息传给ECombination
ECombination.FieldName1 =Trim(cboFieldName1.Text)
ECombination.FieldName2 =Trim(cboFieldName2.Text)
ECombination.FieldName3 =Trim(cboFieldName3.Text)
ECombination.Operator1 =Trim(cboOperator1.Text)
ECombination.Operator2 =Trim(cboOperator2.Text)
ECombination.Operator3 =Trim(cboOperator3.Text)
ECombination.CompositionRelation1 =Trim(cboCompositionRelation1.Text)
ECombination.CompositionRelation2 =Trim(cboCompositionRelation2.Text)
ECombination.ChcekContent1 =Trim(txtChcekContent1.Text)
ECombination.ChcekContent2 =Trim(txtChcekContent2.Text)
ECombination.ChcekContent3 =Trim(txtChcekContent3.Text)
'组合查询
dt =BCombination.CombinationCheck(ECombination)
'把查到的结果传给gvwViewOperatorWorkRecord控件显示出来
gvwViewOperatorWorkRecord.DataSource =dt
End Sub
Private Sub BtnExit_Click(ByVal sender AsSystem.Object, ByVal e As System.EventArgs) Handles BtnExit.Click
Me.Hide()
End Sub
End Class
B层代码
Public ClassBLLOperatorWorkRecord
''' <summary>
''' 组合查询
''' </summary>
''' <paramname="Combination"></param>
''' <returns></returns>
''' <remarks></remarks>
Function CombinationCheck(ByVal CombinationAs Entity.Combination) As DataTable
Dim ECombination As NewEntity.Combination '定义一个实体类
Dim DCombiantion As NewDAL.DALWorkLogInfo '定义一个DALWorkLogInfo来调用D层的方法
Dim strSqlString As String '定义一个存SQL语句
Dim dt As New DataTable'定义一个DataTable来存储查询出来的语句
ECombination = Combination '把传过来的值传给ECombination
strSqlString =CombinationSqlString(ECombination) '调用 CombinationSqlString函数来拼接sql语句
dt =DCombiantion.CheckWorkLogInfo(strSqlString)'调用D层的CheckWorkLogInfo方法来查询，并把查询到的结果传给dt
Return dt
End Function
''' <summary>
''' 改变把中文字符编程英文
''' </summary>
''' <paramname="Field"></param>
''' <returns></returns>
''' <remarks></remarks>
Function ChangeField(ByVal Field As String)As String
Select Case Field
Case "教师"
Field = " OperatorID "
Case "级别"
Field = " OperatorLevel "
Case "登录日期"
Field = " LogonDate "
Case "登录时间"
Field = " LogonTime "
Case "注销日期"
Field = " LogOutDate "
Case "注销时间"
Field = " LogOutTime "
Case "机器名"
Field = " OperatorUseComputer "
Case "或"
Field = " or "
Case "与"
Field = " and "
End Select
Return Field
End Function
''' <summary>
''' 组合条件
''' </summary>
''' <paramname="Combination"></param>
''' <returns></returns>
''' <remarks></remarks>
Function CombinationSqlString(ByValCombination As Entity.Combination) As String
Dim ECombination As NewEntity.Combination '定义一个实体类
'定义字符串存储查询的内容
Dim strSqlString1 As String
Dim strSqlString2 As String
Dim strSqlString3 As String
Dim strSqlAll As String
ECombination = Combination
'拼接sql字符串
ECombination.FieldName1 =ChangeField(Combination.FieldName1)
ECombination.FieldName2 =ChangeField(Combination.FieldName2)
ECombination.FieldName3 =ChangeField(Combination.FieldName3)
ECombination.ChcekContent1 ="'" + Combination.ChcekContent1 + "'"
ECombination.ChcekContent2 ="'" + Combination.ChcekContent2 + "'"
ECombination.ChcekContent3 ="'" + Combination.ChcekContent3 + "'"
ECombination.CompositionRelation1 =ChangeField(Combination.CompositionRelation1)
ECombination.CompositionRelation2 =ChangeField(Combination.CompositionRelation2)
strSqlString1 = ECombination.FieldName1+ ECombination.Operator1 + ECombination.ChcekContent1 +ECombination.CompositionRelation1
strSqlString2 = ECombination.FieldName2+ ECombination.Operator2 + ECombination.ChcekContent2 +ECombination.CompositionRelation2
strSqlString3 = ECombination.FieldName3+ ECombination.Operator3 + ECombination.ChcekContent3
'检查某些字符串为空的情况
Select Case True
Case ECombination.FieldName2 ="" And ECombination.CompositionRelation1 <> ""
strSqlString1 =ECombination.FieldName1 + ECombination.Operator1 + ECombination.ChcekContent1
strSqlString2 = ""
strSqlString3 = ""
Case ECombination.FieldName3 ="" And ECombination.CompositionRelation2 <> ""
strSqlString2 =ECombination.FieldName2 + ECombination.Operator2 + ECombination.ChcekContent2
strSqlString3 = ""
strSqlAll =AddString(strSqlString1, strSqlString2, strSqlString3)
CaseECombination.CompositionRelation1 = ""
strSqlString1 =ECombination.FieldName1 + ECombination.Operator1 + ECombination.ChcekContent1
strSqlString2 = ""
strSqlString3 = ""
CaseECombination.CompositionRelation2 = ""
strSqlString2 =ECombination.FieldName2 + ECombination.Operator2 + ECombination.ChcekContent2
strSqlString3 = ""
End Select
'把查询字符串拼接在一起
strSqlAll = AddString(strSqlString1,strSqlString2, strSqlString3)
Return strSqlAll
End Function
''' <summary>
''' 字符串拼接
''' </summary>
''' <paramname="str1"></param>
''' <paramname="str2"></param>
''' <paramname="str3"></param>
''' <returns></returns>
''' <remarks></remarks>
Function AddString(ByVal str1 As String,ByVal str2 As String, ByVal str3 As String) As String
Dim strAllString As String
strAllString = str1 + str2 + str3
Return strAllString
End Function
End Class
D层：
''' <summary>
''' 组合查询
''' </summary>
'''
''' <returns></returns>
''' <remarks></remarks>
Function CheckWorkLogInfo(ByValstrCombinationSQL As String) As DataTable
Dim strSql As String ="select OperatorID as教师,OperatorLevel as 级别,LogonDate as 登录日期,LogonTime as 登录时间,LogOutDate as注销日期,LogOutTime as 注销时间,OperatorUseComputer as 机器名 from WorkLog_Info where" + strCombinationSQL‘SQL语句
Dim cmd As SqlCommand = NewSqlCommand(strSQL, conn)’连接数据库
Dim sqlda As NewSqlDataAdapter‘建一个SQLDataAdapter
Dim ds As New DataSet’定义一个新的DataSet
Dim dt As NewDataTable‘定义一个新的DataTable
Try
conn.Open()’打开数据库
sqlda.SelectCommand = cmd‘把cmd传给da
sqlda.Fill(dt)’填充dt
Return dt
Catch ex As Exception
Return dt
Finally
cmd.Dispose()
conn.Close()
End Try
End Function