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【摘 要】 本文介绍微软最新技术Visual Basic.NET在数据库开发方面的应用。结合数据库系统开发的知识，介绍了物理表操作的方法，利用Visual Basic.NET的&&keyword=%C3%E6%CF%F2%B6%D4%CF%F3">面向对象的特征，利用类的继承知识，简化了数据库系统开发过程。

　　引言

　　以前版本的Visual Basic虽然号称自己是一种OOP（&&keyword=%C3%E6%CF%F2%B6%D4%CF%F3">面向对象）编程语言，但却不是一个地地道道的OOP编程语言，最多只是半个&&keyword=%C3%E6%CF%F2%B6%D4%CF%F3">面向对象的编程语言。但Visual Basic.NET已经是一种完全的&&keyword=%C3%E6%CF%F2%B6%D4%CF%F3">面向对象的编程语言。他支持&&keyword=%C3%E6%CF%F2%B6%D4%CF%F3">面向对象的所有基本特征：继承、多态和重载。这使得以前在Visual Basic中很难或根本实现不了的问题，在Visual Basic.NET中可以顺利的用简单的方法实现。

　　自定义数据操作类

　　定义一个数据访问的基类，并编写有关数据库操作的必要方法。

　　定义一个数据访问类，类名为CData。定义连接Oracle数据库的方法ConnOracle，获取数据集的方法GetDataSet, 获取物理表的方法GetDataTable, 向物理表中插入一行数据的方法Insert, 向物理表中删除数据的方法Delete, 向物理表中更新数据的方法Update。其实现方法不是本文的重点，在此仅给出代码，不作详细分析。代码如下：

Public Class CDataBase Dim OleCnnDB As New OleDbConnection() '连接Oracle数据库，ServerName:服务器名，UserId:用户名，UserPwd:用户密码 Public Function ConnOracle(ByVal ServerName As String, ByVal UserId As String, ByVal UserPwd As String) As OleDbConnection 　Dim OleCnnDB As New OleDbConnection() 　With OleCnnDB 　　.ConnectionString = "Provider=MSDAORA.1;Password='" & UserPwd & "';User ID='" & UserId & "';Data Source='" & ServerName & "'" 　　Try 　　　.Open() 　　Catch er As Exception 　　　MsgBox(er.ToString) 　　End Try 　End With 　mOleCnnDB = OleCnnDB 　Return OleCnnDB End Function '获取数据集。TableName：表名，strWhere：条件 Public Overloads Function GetDataSet(ByVal TableName As String, ByVal strWhere As String) As DataSet 　Dim strSql As String 　Dim myDataSet As New DataSet() 　Dim myOleDataAdapter As New OleDbDataAdapter() 　myOleDataAdapter.TableMappings.Add(TableName, TableName) 　strSql = "SELECT * FROM " & TableName & " where " & strWhere 　myOleDataAdapter.SelectCommand = New OleDbCommand(strSql, mOleCnnDB) 　Try 　　myOleDataAdapter.Fill(myDataSet) 　Catch er As Exception 　　MsgBox(er.ToString) 　End Try 　Return myDataSet End Function '获取物理表。TableName：表名 Public Overloads Function GetDataTable(ByVal TableName As String) As DataTable 　Dim myDataSet As New DataSet() 　myDataSet = GetDataSet(TableName) 　Return myDataSet.Tables(0) End Function '获取物理表。TableName：表名，strWhere：条件 Public Overloads Function GetDataTable(ByVal TableName As String, ByVal strWhere As String) As DataTable 　Dim myDataSet As New DataSet() 　myDataSet = GetDataSet(TableName, strWhere) 　Return myDataSet.Tables(0) End Function 　'向物理表中插入一行数据。TableName：表名，Value：行数据，BeginColumnIndex：开始列 Public Overloads Function Insert(ByVal TableName As String, ByVal Value As Object, Optional ByVal BeginColumnIndex As Int16 = 0) As Boolean 　Dim myDataAdapter As New OleDbDataAdapter() 　Dim strSql As String 　Dim myDataSet As New DataSet() 　Dim dRow As DataRow 　Dim i, len As Int16 　strSql = "SELECT * FROM " & TableName 　myDataAdapter.SelectCommand = New OleDbCommand(strSql, mOleCnnDB) 　Dim custCB As OleDbCommandBuilder = New OleDbCommandBuilder(myDataAdapter) 　myDataSet.Tables.Add(TableName) 　myDataAdapter.Fill(myDataSet, TableName) 　dRow = myDataSet.Tables(TableName).NewRow 　len = Value.Length 　For i = BeginColumnIndex To len - 1 　　If Not (IsDBNull(Value(i)) Or IsNothing(Value(i))) Then 　　　dRow.Item(i) = Value(i) 　　End If 　Next 　myDataSet.Tables(TableName).Rows.Add(dRow) 　Try 　　myDataAdapter.Update(myDataSet, TableName) 　Catch er As Exception 　　MsgBox(er.ToString) 　　Return False 　End Try 　myDataSet.Tables.Remove(TableName) 　Return True End Function '更新物理表的一个字段的值。strSql：查询语句，FieldName_Value：字段及与对应的值 Public Overloads Sub Update(ByVal strSql As String, ByVal FieldName_Value As String) 　Dim myDataAdapter As New OleDbDataAdapter() 　Dim myDataSet As New DataSet() 　Dim dRow As DataRow 　Dim TableName, FieldName As String 　Dim Value As Object 　Dim a() As String 　a = strSql.Split(" ") 　TableName = a(3) 　a = FieldName_Value.Split("=") 　FieldName = a(0).Trim 　Value = a(1) 　myDataAdapter.SelectCommand = New OleDbCommand(strSql, mOleCnnDB) 　Dim custCB As OleDbCommandBuilder = New OleDbCommandBuilder(myDataAdapter) 　myDataSet.Tables.Add(TableName) 　myDataAdapter.Fill(myDataSet, TableName) 　dRow = myDataSet.Tables(TableName).Rows(0) 　If Value <> Nothing Then 　　dRow.Item(FieldName) = Value 　End If 　Try 　　myDataAdapter.Update(myDataSet, TableName) 　　myDataSet.Tables.Remove(TableName) 　Catch er As Exception 　　MsgBox(er.ToString) 　End Try End Sub '删除物理表的数据。TableName:表名，strWhere：条件 Public Overloads Sub Delete(ByVal TableName As String, ByVal strWhere As String) 　Dim myReader As OleDbDataReader 　Dim myCommand As New OleDbCommand() 　Dim strSql As String 　strSql = "delete FROM " & TableName & " where " & strWhere 　myCommand.Connection = mOleCnnDB 　myCommand.CommandText = strSql 　Try 　　myReader = myCommand.ExecuteReader() 　　myReader.Close() 　Catch er As Exception 　　MsgBox(er.ToString) 　End Try End Sub End Class

　定义一操作数据库中物理表的类CData,此类继承CDataBase,即：

Public Class CData：Inherits CDataBase

　　此类应该由供用户提供所操作的物理表的表名，指定了表名就可取得该表的所有性质。该表主要完成插入、删除、更新功能。定义其&&属性、方法如下：

　　申明类CData的变量:

'所要操作的表名 Private Shared UpdateTableName As String '所要操作的表对象 Public Shared UpdateDataTable As New DataTable() '对应表的一行数据197 Public Shared ObjFields() As Object '表的字段数 Public Shared FieldCount As Int16 '主关键字。我们假设每个物理表都有一个主关键字字段fSystemID Public Shared SystemID As String

　　说明：Shared 关键字指示一个或多个被声明的编程元素将被共享。共享元素不关联于某类或结构的特定实例。可以通过使用类名或结构名称或者类或结构的特定实例的变量名称限定共享元素来访问它们。

　　申明类CData的&&属性UpdateTable,当向UpdateTable赋给了一个已知表的表名，就可确定表的字段数，定义出数据行。这里，先打开表，再重新定义数据行.

Public Property UpdateTable() As String 　Get 　　UpdateTable = UpdateTableName 　End Get 　Set(ByVal Value As String) 　　UpdateTableName = Value.Trim 　　UpdateDataTable = DB.GetDataTable(UpdateTableName) 　　UpdateTableFieldNames = UpdateDataTable.Clone 　　FieldCount = UpdateDataTable.Columns.Count 　　ReDim ObjFields(FieldCount - 1) 　End Set End Property '删除由主关键值fSystemID指定的数据行 Public Sub Delete() 　Dim strSQL As String 　strSQL = "Delete from " & UpdateTableName & " where fSystemID=" & SystemID 　DB.Delete(strSQL) 　UpdateDataTable.Rows.Remove(GetRow) End Sub '向表UpdateTableName中插入一行数据。数据由ObjFields给出 Public Function Insert() As Boolean 　DB.Insert(UpdateTableName, ObjFields) End Function '更新表UpdateTableName所指定的行 Public Shadows Sub Update() 　Dim SetField As String 　Dim i As Int16 　For i = 1 To FieldCount - 1 　　SetField = UpdateTableFieldNames.Columns(i).ColumnName & "=" & ObjFields(i) 　　UpdateField(SetField) 　Next End Sub Public Sub UpdateField(ByVal SetField As String) 　Dim StrSQL As String 　StrSQL = "select * from " & UpdateTableName & " where fSystemID= " & SystemID 　DB.Update(StrSQL, SetField) End Sub '填充网络数据 Public Overloads Sub FillGrid(ByVal GridName As DataGrid) 　GridName.DataSource = UpdateDataTable End Sub '把数据网格的当前行数据定写入到输入控件中 Public Sub DataGridToText(ByVal frm As Form) 　Dim RowIndex, i As Int16 　Dim value 　Dim obj As Control 　Dim DataGrid As New DataGrid() 　If FieldCount = 0 Then Exit Sub 　　For Each obj In frm.Controls 　　　If obj.GetType.Name = "DataGrid" Then 　　　　DataGrid = obj 　　　　Exit For 　　　End If 　　Next 　　RowIndex = DataGrid.CurrentRowIndex 　　For i = 1 To FieldCount - 1 　　　value = DataGrid.Item(RowIndex, i) 　　　If IsDBNull(value) = True Then 　　　　value = "" 　　　End If 　　　For Each obj In frm.Controls ' 　　　　If obj.TabIndex = i Then 　　　　　obj.Text = value 　　　　　Exit For 　　　　End If 　　　Next 　　Next End Sub