历经n多天。组合查询模板最终做完了，总结一下这几天的成果。和大家一起学习交流。

先看一下父窗口的关键代码：

父窗口代码：

Public Class frmComboQueryProtected Overridable Sub frmComboQuery_Load(sender As Object, e As EventArgs) Handles MyBase.LoadDim ComboxArray(4) As ComboBox            '定义控件数组，获取组合框ComboxArray(0) = cboOperator1ComboxArray(1) = cboOperator2ComboxArray(2) = cboOperator3ComboxArray(3) = cboRelation1ComboxArray(4) = cboRelation2CommonMethod.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) = cboField2ControlArray(1) = cboOperator2ControlArray(2) = txtContent2ControlArray(3) = cboRelation2ControlArray(4) = cboField3ControlArray(5) = cboOperator3ControlArray(6) = txtContent3CommonMethod.LockControlArray(ControlArray)        '调用共同拥有方法，锁定控件End SubPrivate Sub btnQuery_Click(sender As Object, e As EventArgs) Handles btnQuery.ClickTryDim ControlArray(2) As Control             '定义控件数组，获取组合1的控件ControlArray(0) = cboField1ControlArray(1) = cboOperator1ControlArray(2) = txtContent1If CommonMethod.IsEmptyControlArray(ControlArray) = False Then           '推断组合1的控件是否为空Exit SubEnd IfIf 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) = cboOperator2ControlArray(2) = txtContent2If CommonMethod.IsEmptyControlArray(ControlArray) = False Then      '推断组合2的条件是否为空Exit SubEnd IfIf 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) = cboOperator3ControlArray(2) = txtContent3If CommonMethod.IsEmptyControlArray(ControlArray) = False Then     '推断组合3的条件是否为空Exit SubEnd IfEnd IfEnd IfDim 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.TrimeComboQuery1.Field2 = cboField2.Text.TrimeComboQuery1.Field3 = cboField3.Text.TrimeComboQuery1.Operator1 = cboOperator1.Text.TrimeComboQuery1.Operator2 = cboOperator2.Text.TrimeComboQuery1.Operator3 = cboOperator3.Text.TrimeComboQuery1.Content1 = txtContent1.Text.TrimeComboQuery1.Content2 = txtContent2.Text.TrimeComboQuery1.Content3 = txtContent3.Text.TrimeComboQuery1.Relation1 = cboRelation1.Text.TrimeComboQuery1.Relation2 = cboRelation2.Text.TrimDim dtComboQuery As New DataTableDim mgr As New BLL.ComboQueryBLLdtComboQuery = mgr.ComboQuery(eComboQuery1)dgvRecord.DataSource = dtComboQueryCatch ex As ExceptionMessageBox.Show(ex.Message.ToString())dgvRecord.DataSource = NothingEnd TryEnd SubProtected Overridable Function GetdbName() As StringReturn ""End FunctionPrivate Sub cboRelation1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cboRelation1.SelectedIndexChangedDim 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) = cboField2ControlArray(1) = cboOperator2ControlArray(2) = txtContent2ControlArray(3) = cboRelation2If cboRelation1.SelectedIndex = 0 Then               '假设组合关系1为空，清空组合2和组合关系2CommonMethod.ClearControlArray(ControlArray)CommonMethod.LockControlArray(ControlArray)ElseCommonMethod.UnLockControlArray(ControlArray)                 '否则。解锁组合2和组合关系2End IfEnd SubPrivate Sub cboRelation2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cboRelation2.SelectedIndexChangedDim ControlArray(2) As Control                   '定义控件数组，获取组合3的控件ControlArray(0) = cboField3ControlArray(1) = cboOperator3ControlArray(2) = txtContent3If cboRelation2.SelectedIndex = 0 Then               '假设组合关系2为空。清空组合2。锁定组合3CommonMethod.ClearControlArray(ControlArray)CommonMethod.LockControlArray(ControlArray)ElseCommonMethod.UnLockControlArray(ControlArray)                '否则，解锁组合3End IfEnd Sub
End Class

文中调用的公共方法上篇博客已写，这里不再反复。

如今以查询操作员工作记录为例：

Public Class frmWorkLogProtected 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) = cboField1ComboxArray(1) = cboField2ComboxArray(2) = cboField3CommonMethod.SelectIndex(ComboxArray)           '设置combox默认显示第一项End SubProtected Overrides Function GetdbName() As StringReturn "WorkLog"End Function
End Class

说明：1.设置默认第一项在父窗口加入了一部分，这里是字段的那部分，由于字段是在子窗口加入，所以假设这段代码也放父窗口会报错。

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，可是临时没有想到其它方法。仅仅能先这么写。
B层代码：

Public Class ComboQueryBLLDim factory As New Factory.DataAccessPublic Function ComboQuery(ByVal cboworklog As Entity.ComboQueryEntity) As DataTableDim iComboQuery As IDAL.IComboQueryiComboQuery = factory.CreateComboQueryDim dtComboQuery As New DataTabledtComboQuery = iComboQuery.ComboQuery(cboworklog)If dtComboQuery.Rows.Count = 0 ThenThrow New Exception("没有记录")ElseReturn dtComboQueryEnd IfEnd Function
End Class

D层代码：

Imports System.Data.SqlClient
Public Class SqlServerComboQueryDAL : Implements IDAL.IComboQueryDim sqlhelper As New SqlHelperPublic Function ComboQuery1(cboworklog As Entity.ComboQueryEntity) As DataTable Implements IDAL.IComboQuery.ComboQueryDim ecboworklog As New Entity.ComboQueryEntitySelect Case cboworklog.dbNameCase "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 SelectDim 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 DataTabledtComboQuery = sqlhelper.Query("sp_ComboQuery", CommandType.StoredProcedure, sqlParameter)Return dtComboQueryEnd 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。暂时存放字段值Dim Field(2) As StringField(0) = eworklog.Field1Field(1) = eworklog.Field2Field(2) = eworklog.Field3For 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 ElsestrField(i) = ""End SelectField(i) = strField(i)Nexteworklog.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，暂时存在关系值Dim Relation(1) As StringRelation(0) = eworklog.Relation1Relation(1) = eworklog.Relation2For 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 ElsestrRelation(i) = ""End SelectRelation(i) = strRelation(i)Nexteworklog.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
BEGINDECLARE @sqlText varchar(200)SET @sqlText='SELECT * FROM '+@dbName+' WHERE ' +@field1 +@operator1+char(39) + @content1 + char(39)if @relation1<>''BEGINSET @sqlText=@sqlText+@relation1+CHAR(32)+@field2+@operator2+CHAR(39)+@content2+CHAR(39)if @relation2<>''BEGINSET @sqlText=@sqlText+@relation2+CHAR(32)+@field3+@operator3+CHAR(39)+@content3+CHAR(39)ENDENDEXECUTE(@sqlText)
END

效果例如以下：

题外话：

由于系统多次用到组合查询，并且各个窗口很类似，所以最初仅仅是想到用窗口的继承，免得做反复的窗口。后来父窗口做好之后，发现那些推断是否为空、清空等代码能够写到父窗口。然后子窗口写关于查询的代码。

紧接着就出现了一个问题，使用窗口继承。对于同一个事件而言，程序会先运行父窗口中的代码，后运行子窗口中的代码。在我的程序里，当运行button的click事件时，父窗口会先推断组合框是否为空。假设推断出为空，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，而是接着运行子窗口的查询。

后来仅仅好请教师父和师哥，得到一个解决的方法。就是声明一个全局变量，由它通知子窗口是否运行，同一时候师哥指出，事实上子窗口的代码也能够放在父窗口中，我自己也认为声明全局变量感觉不好。所以就演化到如今的样子了。后来才知道，不知不觉还用了一个设计模式。模板方法模式。

只是这个模式依旧须要子窗口去传递一个參数，让D层去推断是用的哪一个数据库，感觉不好，可是也没有想出好的办法。假设大家有什么好的建议。望不吝奉献。