历经n多天，组合查询模板终于做完了，总结一下这几天的成果，和大家一起学习交流。
先看一下父窗体的关键代码：
父窗体代码：
Public Class frmComboQuery
Protected Overridable Sub frmComboQuery_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim ComboxArray(4) As ComboBox '定义控件数组，获取组合框
ComboxArray(0) = cboOperator1
ComboxArray(1) = cboOperator2
ComboxArray(2) = cboOperator3
ComboxArray(3) = cboRelation1
ComboxArray(4) = cboRelation2
CommonMethod.SelectIndex(ComboxArray) '设置combox默认显示第一项
Dim ControlArray(6) As Control '定义控件数组，获取组合2和组合3的控件
ControlArray(0) = cboField2
ControlArray(1) = cboOperator2
ControlArray(2) = txtContent2
ControlArray(3) = cboRelation2
ControlArray(4) = cboField3
ControlArray(5) = cboOperator3
ControlArray(6) = txtContent3
CommonMethod.LockControlArray(ControlArray) '调用共有方法，锁定控件
End Sub
Private Sub btnQuery_Click(sender As Object, e As EventArgs) Handles btnQuery.Click
Try
Dim ControlArray(2) As Control '定义控件数组，获取组合1的控件
ControlArray(0) = cboField1
ControlArray(1) = cboOperator1
ControlArray(2) = txtContent1
If CommonMethod.IsEmptyControlArray(ControlArray) = False Then '判断组合1的控件是否为空
Exit Sub
End If
If cboRelation1.Text.Trim <> "<请选择>" Then '组合关系1不为空时
ControlArray(0) = cboField2 '获取组合2的控件
ControlArray(1) = cboOperator2
ControlArray(2) = txtContent2
If CommonMethod.IsEmptyControlArray(ControlArray) = False Then '判断组合2的条件是否为空
Exit Sub
End If
If cboRelation2.Text.Trim <> "<请选择>" Then '组合关系2不为空时
ControlArray(0) = cboField3 '获取组合3的控件
ControlArray(1) = cboOperator3
ControlArray(2) = txtContent3
If CommonMethod.IsEmptyControlArray(ControlArray) = False Then '判断组合3的条件是否为空
Exit Sub
End If
End If
End If
Dim eComboQuery1 As New Entity.ComboQueryEntity '定义组合查询实体，将条件传入实体
eComboQuery1.dbName = GetdbName()
eComboQuery1.Field1 = cboField1.Text.Trim
eComboQuery1.Field2 = cboField2.Text.Trim
eComboQuery1.Field3 = cboField3.Text.Trim
eComboQuery1.Operator1 = cboOperator1.Text.Trim
eComboQuery1.Operator2 = cboOperator2.Text.Trim
eComboQuery1.Operator3 = cboOperator3.Text.Trim
eComboQuery1.Content1 = txtContent1.Text.Trim
eComboQuery1.Content2 = txtContent2.Text.Trim
eComboQuery1.Content3 = txtContent3.Text.Trim
eComboQuery1.Relation1 = cboRelation1.Text.Trim
eComboQuery1.Relation2 = cboRelation2.Text.Trim
Dim dtComboQuery As New DataTable
Dim mgr As New BLL.ComboQueryBLL
dtComboQuery = mgr.ComboQuery(eComboQuery1)
dgvRecord.DataSource = dtComboQuery
Catch ex As Exception
MessageBox.Show(ex.Message.ToString())
dgvRecord.DataSource = Nothing
End Try
End Sub
Protected Overridable Function GetdbName() As String
Return ""
End Function
Private Sub cboRelation1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cboRelation1.SelectedIndexChanged
Dim ControlArray(3) As Control '定义控件数组，获取组合2的控件和组合关系2的控件，
ControlArray(0) = cboField2
ControlArray(1) = cboOperator2
ControlArray(2) = txtContent2
ControlArray(3) = cboRelation2
If cboRelation1.SelectedIndex = 0 Then '如果组合关系1为空，清空组合2和组合关系2
CommonMethod.ClearControlArray(ControlArray)
CommonMethod.LockControlArray(ControlArray)
Else
CommonMethod.UnLockControlArray(ControlArray) '否则，解锁组合2和组合关系2
End If
End Sub
Private Sub cboRelation2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cboRelation2.SelectedIndexChanged
Dim ControlArray(2) As Control '定义控件数组，获取组合3的控件
ControlArray(0) = cboField3
ControlArray(1) = cboOperator3
ControlArray(2) = txtContent3
If cboRelation2.SelectedIndex = 0 Then '如果组合关系2为空，清空组合2，锁定组合3
CommonMethod.ClearControlArray(ControlArray)
CommonMethod.LockControlArray(ControlArray)
Else
CommonMethod.UnLockControlArray(ControlArray) '否则，解锁组合3
End If
End Sub
End Class
文中调用的公共方法上篇博客已写，这里不再重复。
现在以查询操作员工作记录为例：
Public Class frmWorkLog
Protected Overrides Sub frmComboQuery_Load(sender As Object, e As EventArgs)
MyBase.frmComboQuery_Load(sender, e)
Dim ComboxArray(2) As ComboBox '定义控件数组，获取组合框
ComboxArray(0) = cboField1
ComboxArray(1) = cboField2
ComboxArray(2) = cboField3
CommonMethod.SelectIndex(ComboxArray) '设置combox默认显示第一项
End Sub
Protected Overrides Function GetdbName() As String
Return "WorkLog"
End Function
End Class
说明：1.设置默认第一项在父窗体添加了一部分，这里是字段的那部分，因为字段是在子窗体添加，所以如果这段代码也放父窗体会报错。2.这里通过传递一个字符串来通知D层确定哪一个数据表，这里是我感觉不好的地方，但是暂时没有想到其他方法，只能先这么写。
B层代码：
Public Class ComboQueryBLL
Dim factory As New Factory.DataAccess
Public Function ComboQuery(ByVal cboworklog As Entity.ComboQueryEntity) As DataTable
Dim iComboQuery As IDAL.IComboQuery
iComboQuery = factory.CreateComboQuery
Dim dtComboQuery As New DataTable
dtComboQuery = iComboQuery.ComboQuery(cboworklog)
If dtComboQuery.Rows.Count = 0 Then
Throw New Exception("没有记录")
Else
Return dtComboQuery
End If
End Function
End Class
D层代码：
Imports System.Data.SqlClient
Public Class SqlServerComboQueryDAL : Implements IDAL.IComboQuery
Dim sqlhelper As New SqlHelper
Public Function ComboQuery1(cboworklog As Entity.ComboQueryEntity) As DataTable Implements IDAL.IComboQuery.ComboQuery
Dim ecboworklog As New Entity.ComboQueryEntity
Select Case cboworklog.dbName
Case "WorkLog"
ecboworklog = Method.SwitchWorklogField(cboworklog) '调用方法，转换字段，以匹配数据库
Case "StudentAccount"
ecboworklog = Method.SwitchStudentAccount(cboworklog)
End Select
Dim sqlParameter As SqlParameter()
sqlParameter = New SqlParameter() {
New SqlParameter("@dbName", ecboworklog.dbName),
New SqlParameter("@Field1", ecboworklog.Field1),
New SqlParameter("@Field2", ecboworklog.Field2),
New SqlParameter("@Field3", ecboworklog.Field3),
New SqlParameter("@Operator1", ecboworklog.Operator1),
New SqlParameter("@Operator2", ecboworklog.Operator2),
New SqlParameter("@Operator3", ecboworklog.Operator3),
New SqlParameter("@Content1", ecboworklog.Content1),
New SqlParameter("@Content2", ecboworklog.Content2),
New SqlParameter("@Content3", ecboworklog.Content3),
New SqlParameter("@Relation1", ecboworklog.Relation1),
New SqlParameter("@Relation2", ecboworklog.Relation2)}
Dim dtComboQuery As New DataTable
dtComboQuery = sqlhelper.Query("sp_ComboQuery", CommandType.StoredProcedure, sqlParameter)
Return dtComboQuery
End Function
End Class
D层转换字段的方法：
Function SwitchWorklogField(ByVal eworklog As Entity.ComboQueryEntity)
Dim strField(2) As String '字符串数组，临时存放字段值
Dim Field(2) As String
Field(0) = eworklog.Field1
Field(1) = eworklog.Field2
Field(2) = eworklog.Field3
For i = 0 To 2 '通过一个循环对字段进行匹配
Select Case Field(i)
Case "职工ID"
strField(i) = "UserID"
Case "登陆日期"
strField(i) = "LoginDate"
Case "登陆时间"
strField(i) = "LoginTime"
Case "注销日期"
strField(i) = "LogOffDate"
Case "注销时间"
strField(i) = "LogOffTime"
Case "电脑名"
strField(i) = "ComputerName"
Case Else
strField(i) = ""
End Select
Field(i) = strField(i)
Next
eworklog.Field1 = Field(0) '将字段值进行匹配，并赋值给组合查询实体
eworklog.Field2 = Field(1)
eworklog.Field3 = Field(2)
Dim strRelation(1) As String '定义字符串数组，临时存在关系值
Dim Relation(1) As String
Relation(0) = eworklog.Relation1
Relation(1) = eworklog.Relation2
For i = 0 To 1 '循环匹配字段
Select Case Relation(i)
Case "或"
strRelation(i) = "OR"
Case "且"
strRelation(i) = "AND"
Case Else
strRelation(i) = ""
End Select
Relation(i) = strRelation(i)
Next
eworklog.Relation1 = Relation(0) '组合查询实体赋值
eworklog.Relation2 = Relation(1)
eworklog.dbName = "T_WorkLog"
Return eworklog '返回实体
End Function
存储过程代码：
USE [ChargeSystem] GO /****** Object: StoredProcedure [dbo].[sp_ComboQuery] Script Date: 2014/6/22 16:40:59 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO -- ============================================= -- Author: 刘晓春 -- Create date: 2014年6月17日 -- Description: 组合查询 -- ============================================= CREATE PROCEDURE [dbo].[sp_ComboQuery] @dbName varchar(20), @field1 varchar(20),@operator1 varchar(20),@content1 varchar(20), @relation1 varchar(10), @field2 varchar(20),@operator2 varchar(20),@content2 varchar(20), @relation2 varchar(20), @field3 varchar(20),@operator3 varchar(20),@content3 varchar(20) AS BEGIN DECLARE @sqlText varchar(200) SET @sqlText='SELECT * FROM '+@dbName+' WHERE ' +@field1 +@operator1+char(39) + @content1 + char(39) if @relation1<>'' BEGIN SET @sqlText=@sqlText+@relation1+CHAR(32)+@field2+@operator2+CHAR(39)+@content2+CHAR(39) if @relation2<>'' BEGIN SET @sqlText=@sqlText+@relation2+CHAR(32)+@field3+@operator3+CHAR(39)+@content3+CHAR(39) END END EXECUTE(@sqlText) END
效果如下：
题外话：
因为系统多次用到组合查询，而且各个窗体非常类似，所以最初只是想到用窗体的继承，免得做重复的窗体。后来父窗体做好之后，发现那些判断是否为空、清空等代码可以写到父窗体，然后子窗体写关于查询的代码。
紧接着就出现了一个问题，使用窗体继承，对于同一个事件而言，程序会先执行父窗体中的代码，后执行子窗体中的代码。在我的程序里，当执行按钮的click事件时，父窗体会先判断组合框是否为空，如果判断出为空，给出了提示，当点完确定后，程序并没有像想象中那样停下来让你选择组合框，而是接着执行子窗体的查询。
后来只好请教师父和师哥，得到一个解决办法，就是声明一个全局变量，由它通知子窗体是否执行，同时师哥指出，其实子窗体的代码也可以放在父窗体中，我自己也觉得声明全局变量感觉不好，所以就演化到现在的样子了，后来才知道，不知不觉还用了一个设计模式，模板方法模式。
不过这个模式依然需要子窗体去传递一个参数，让D层去判断是用的哪一个数据库，感觉不好，但是也没有想出好的办法，如果大家有什么好的建议，望不吝奉献。