一．改进
在DAAB1.1里面我们知道Database方法返回或者创建一个DBCommandWrapper对象，而在DAAB2.0里面移除了DBCommandWrapper类，用ADO.NET2.0里面的DBCommand类代替实现类似的功能，这样使得DAAB跟我们的.NET类库的结合更加紧密，回忆一下我们在1.1里面用DBCommandWrapper来访问数据时的代码：
Database db = DatabaseFactory.CreateDatabase(); DBCommandWrapper dbCommand = db.GetStoredProcCommandWrapper("GetProductsByCategory"); dbCommand.AddInParameter("CategoryID", DbType.Int32, Category); DataSet productDataSet = db.ExecuteDataSet(dbCommand); 而用了新的DBCommand类之后则变成了：
Database db = DatabaseFactory.CreateDatabase(); DbCommand dbCommand = db.GetStoredProcCommand("GetProductsByCategory"); db.AddInParameter(dbCommand, "CategoryID", DbType.Int32, Category); DataSet productDataSet = db.ExecuteDataSet(dbCommand); 数据库连接字符串在我们基于数据库的开发永远是少不了的，但是在DAAB1.1下，它所使用的字符串跟我们在.NET类库中使用的连接字符串却是不能共享的，它们分别保存在不同的位置。而在2.0的Data Access Application Block使用了ADO.NET2.0里面<connectionStrings>配置区，这样带来的一个好处是连接字符串可以在Application Block和自定义的.NET类之间共享使用该配置区，如：
<connectionStrings> <add name="DataAccessQuickStart" providerName="System.Data.SqlClient" connectionString="server=(local)\SQLEXPRESS;database=EntLibQuickStarts;Integrated Security=true" /> </connectionStrings> 在.NET2.0下，泛型编程已经成为了一个核心，而2.0版的DAAB中也新增了一个GenericDatabase对象。DAAB中虽然已经包含了SqlDatabase和OrcaleDatabase，但是如果我们需要使用其他的像DB2等数据库时，就需要用到GenericDatabase，它可以用于任何.NET类库中的数据提供者，包括OdbcProvider和OleDbProvider。
二．使用示例
二．使用示例
DAAB2.0的配置非常简单，主要有以下几方面的配置：
配置连接字符串
配置默认数据库
添加相关的命名空间：
using Microsoft.Practices.EnterpriseLibrary.Data; using System.Data; 使用Data Access Application Block进行数据的读取和操作，一般分为三步：
1．创建Database对象
2．提供命令参数，如果需要的话
3．执行命令
下面分别看一下DataAccessQuickStart中提供的一些例子：
执行静态的SQL语句
public string GetCustomerList() 
{ 
// 创建Database对象 Database db = DatabaseFactory.CreateDatabase(); // 使用SQL语句创建DbCommand对象 string sqlCommand = "Select CustomerID, Name, Address, City, Country, PostalCode " + "From Customers"; DbCommand dbCommand = db.GetSqlStringCommand(sqlCommand); StringBuilder readerData = new StringBuilder(); // 调用ExecuteReader方法 using (IDataReader dataReader = db.ExecuteReader(dbCommand)) 
{ while (dataReader.Read()) { // Get the value of the 'Name' column in the DataReader readerData.Append(dataReader["Name"]); readerData.Append(Environment.NewLine); 
} } return readerData.ToString(); 
} 执行存储过程并传递参数，返回DataSet
public DataSet GetProductsInCategory(int Category) { // Create the Database object, using the default database service. The // default database service is determined through configuration. Database db = DatabaseFactory.CreateDatabase(); string sqlCommand = "GetProductsByCategory"; DbCommand dbCommand = db.GetStoredProcCommand(sqlCommand); // Retrieve products from the specified category. db.AddInParameter(dbCommand, "CategoryID", DbType.Int32, Category); // DataSet that will hold the returned results DataSet productsDataSet = null; productsDataSet = db.ExecuteDataSet(dbCommand); // Note: connection was closed by ExecuteDataSet method call return productsDataSet; } 利用DataSet更新数据
public int UpdateProducts() { // Create the Database object, using the default database service. The // default database service is determined through configuration. Database db = DatabaseFactory.CreateDatabase(); DataSet productsDataSet = new DataSet(); string sqlCommand = "Select ProductID, ProductName, CategoryID, UnitPrice, LastUpdate " + "From Products"; DbCommand dbCommand = db.GetSqlStringCommand(sqlCommand); string productsTable = "Products"; // Retrieve the initial data db.LoadDataSet(dbCommand, productsDataSet, productsTable); // Get the table that will be modified DataTable table = productsDataSet.Tables[productsTable]; // Add a new product to existing DataSet DataRow addedRow = table.Rows.Add(new object[] {DBNull.Value, "New product", 11, 25}); // Modify an existing product table.Rows[0]["ProductName"] = "Modified product"; // Establish our Insert, Delete, and Update commands DbCommand insertCommand = db.GetStoredProcCommand("AddProduct"); db.AddInParameter(insertCommand, "ProductName", DbType.String, "ProductName", DataRowVersion.Current); db.AddInParameter(insertCommand, "CategoryID", DbType.Int32, "CategoryID", DataRowVersion.Current); db.AddInParameter(insertCommand, "UnitPrice", DbType.Currency, "UnitPrice", DataRowVersion.Current); DbCommand deleteCommand = db.GetStoredProcCommand("DeleteProduct"); db.AddInParameter(deleteCommand, "ProductID", DbType.Int32, "ProductID", DataRowVersion.Current); DbCommand updateCommand = db.GetStoredProcCommand("UpdateProduct"); db.AddInParameter(updateCommand, "ProductID", DbType.Int32, "ProductID", DataRowVersion.Current); db.AddInParameter(updateCommand, "ProductName", DbType.String, "ProductName", DataRowVersion.Current); db.AddInParameter(updateCommand, "LastUpdate", DbType.DateTime, "LastUpdate", DataRowVersion.Current); // Submit the DataSet, capturing the number of rows that were affected int rowsAffected = db.UpdateDataSet(productsDataSet, "Products", insertCommand, updateCommand, deleteCommand, UpdateBehavior.Standard); return rowsAffected; } 通过ID获取记录详细信息
public string GetProductDetails(int productID) { // Create the Database object, using the default database service. The // default database service is determined through configuration. Database db = DatabaseFactory.CreateDatabase(); string sqlCommand = "GetProductDetails"; DbCommand dbCommand = db.GetStoredProcCommand(sqlCommand); // Add paramters // Input parameters can specify the input value db.AddInParameter(dbCommand, "ProductID", DbType.Int32, productID); // Output parameters specify the size of the return data db.AddOutParameter(dbCommand, "ProductName", DbType.String, 50); db.AddOutParameter(dbCommand, "UnitPrice", DbType.Currency, 8); db.ExecuteNonQuery(dbCommand); // Row of data is captured via output parameters string results = string.Format(CultureInfo.CurrentCulture, "{0}, {1}, {2:C} ", db.GetParameterValue(dbCommand, "ProductID"), db.GetParameterValue(dbCommand, "ProductName"), db.GetParameterValue(dbCommand, "UnitPrice")); return results; } 以XML格式返回数据
public string GetProductList() { // Use a named database instance that refers to a SQL Server database. SqlDatabase dbSQL = DatabaseFactory.CreateDatabase() as SqlDatabase; // Use "FOR XML AUTO" to have SQL return XML data string sqlCommand = "Select ProductID, ProductName, CategoryID, UnitPrice, LastUpdate " + "From Products FOR XML AUTO"; DbCommand dbCommand = dbSQL.GetSqlStringCommand(sqlCommand); XmlReader productsReader = null; StringBuilder productList = new StringBuilder(); try { productsReader = dbSQL.ExecuteXmlReader(dbCommand); // Iterate through the XmlReader and put the data into our results. while (!productsReader.EOF) { if (productsReader.IsStartElement()) { productList.Append(productsReader.ReadOuterXml()); productList.Append(Environment.NewLine); } } } finally { // Close the Reader. if (productsReader != null) { productsReader.Close(); } // Explicitly close the connection. The connection is not closed // when the XmlReader is closed. if (dbCommand.Connection != null) { dbCommand.Connection.Close(); } } return productList.ToString(); } 使用事务
public bool Transfer(int transactionAmount, int sourceAccount, int destinationAccount) { bool result = false; // Create the Database object, using the default database service. The // default database service is determined through configuration. Database db = DatabaseFactory.CreateDatabase(); // Two operations, one to credit an account, and one to debit another // account. string sqlCommand = "CreditAccount"; DbCommand creditCommand = db.GetStoredProcCommand(sqlCommand); db.AddInParameter(creditCommand, "AccountID", DbType.Int32, sourceAccount); db.AddInParameter(creditCommand, "Amount", DbType.Int32, transactionAmount); sqlCommand = "DebitAccount"; DbCommand debitCommand = db.GetStoredProcCommand(sqlCommand); db.AddInParameter(debitCommand, "AccountID", DbType.Int32, destinationAccount); db.AddInParameter(debitCommand, "Amount", DbType.Int32, transactionAmount); using (DbConnection connection = db.CreateConnection()) { connection.Open(); DbTransaction transaction = connection.BeginTransaction(); try { // Credit the first account db.ExecuteNonQuery(creditCommand, transaction); // Debit the second account db.ExecuteNonQuery(debitCommand, transaction); // Commit the transaction transaction.Commit(); result = true; } catch { // Rollback transaction transaction.Rollback(); } connection.Close(); return result; } } 三．常见功能
1．创建Database对象
创建一个默认的Database对象
Database dbSvc = DatabaseFactory.CreateDatabase(); 默认的数据库在配置文件中：
<dataConfiguration defaultDatabase="DataAccessQuickStart" /> 创建一个实例Database对象
// Use a named database instance that refers to an arbitrary database type, // which is determined by configuration information. Database myDb = DatabaseFactory.CreateDatabase("DataAccessQuickStart"); 创建一个具体的类型的数据库对象
// Create a SQL database. SqlDatabase dbSQL = DatabaseFactory.CreateDatabase("DataAccessQuickStart") as SqlDatabase; 2．创建DbCommand对象
静态的SQL语句创建一个DbCommand
Database db = DatabaseFactory.CreateDatabase(); string sqlCommand = "Select CustomerID, LastName, FirstName From Customers"; DbCommand dbCommand = db.GetSqlStringCommand(sqlCommand); 存储过程创建一个DbCommand
Database db = DatabaseFactory.CreateDatabase(); DbCommand dbCommand = db.GetStoredProcCommand("GetProductsByCategory"); 3．管理对象
当连接对象打开后，不需要再次连接
Database db = DatabaseFactory.CreateDatabase(); string sqlCommand = "Select ProductID, ProductName From Products"; DbCommand dbCommand = db.GetSqlStringCommand(sqlCommand); // No need to open the connection; just make the call. DataSet customerDataSet = db.ExecuteDataSet(dbCommand); 使用Using及早释放对象
Database db = DatabaseFactory.CreateDatabase(); DbCommand dbCommand = db.GetSqlStringCommand("Select Name, Address From Customers"); using (IDataReader dataReader = db.ExecuteReader(dbCommand)) { // Process results } 4．参数处理
Database类提供了如下的方法，用于参数的处理：
AddParameter. 传递参数给存储过程
AddInParameter. 传递输入参数给存储过程
AddOutParameter. 传递输出参数给存储过程
GetParameterValue. 得到指定参数的值
SetParameterValue. 设定参数值
使用示例如下：
Database db = DatabaseFactory.CreateDatabase(); string sqlCommand = "GetProductDetails"; DbCommand dbCommand = db.GetStoredProcCommand(sqlCommand); db.AddInParameter(dbCommand, "ProductID", DbType.Int32, 5); db.AddOutParameter(dbCommand, "ProductName", DbType.String, 50); db.AddOutParameter(dbCommand, "UnitPrice", DbType.Currency, 8); Database db = DatabaseFactory.CreateDatabase(); DbCommand insertCommand = db.GetStoredProcCommand("AddProduct"); db.AddInParameter(insertCommand, "ProductName", DbType.String, "ProductName", DataRowVersion.Current); db.AddInParameter(insertCommand, "CategoryID", DbType.Int32, "CategoryID", DataRowVersion.Current); db.AddInParameter(insertCommand, "UnitPrice", DbType.Currency, "UnitPrice", DataRowVersion.Current); 四．使用场景
DAAB2.0是对ADO.NET2.0的补充，它允许你使用相同的数据访问代码来支持不同的数据库，您通过改变配置文件就在不同的数据库之间切换。目前虽然只提供SQLServer和Oracle的支持，但是可以通过GenericDatabase和ADO.NET 2.0下的DbProviderFactory对象来增加对其他数据库的支持。如果想要编写出来的数据库访问程序具有更好的移植性，则DAAB2.0是一个不错的选择，但是如果您想要针对特定数据库的特性进行编程，就要用ADO.NET了。
参考：Enterprise Libaray –January 2006帮助文档及QuickStart
好，看到这里俺应该基本懂得使用了，俺就动手试一下SQL和ACCESS数据库自由切换的方法，因俺平时的习惯是使用vb.net写东西，所以只写出vb.net的代码出来，有兴趣的自己改成C#好了，看以下html代码：
<%...@ Page Language="VB" AutoEventWireup="false" CodeFile="sql.aspx.vb" Inherits="sql" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" ><head runat="server"> <title>web3.cn——SQL、Access数据库自由切换</title></head><body> <form id="form1" runat="server"> <div> <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"> <Columns> <asp:BoundField DataField="id" HeaderText="id" SortExpression="id" > <HeaderStyle BackColor="Silver" /> </asp:BoundField> <asp:BoundField DataField="provinceID" HeaderText="provinceID" SortExpression="provinceID" > <HeaderStyle BackColor="Silver" /> </asp:BoundField> <asp:BoundField DataField="province" HeaderText="provinceID" SortExpression="province" > <HeaderStyle BackColor="Silver" /> </asp:BoundField> </Columns> </asp:GridView> </div> </form></body></html>vb.net代码：
Imports System.DataImports Microsoft.Practices.EnterpriseLibrary.DataImports system.Data.CommonImports System.Data.OdbcPartial Class sql_accessClass sql_access Inherits System.Web.UI.Page Dim sys As New WebService Protected Sub Page_Load()Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load If Not Page.IsPostBack Then BindGrid() End If End Sub Sub BindGrid()Sub BindGrid() Dim dv As DataView dv = GetList_Access().DefaultView GridView1.DataSource = dv GridView1.DataBind() End Sub '列表 Public Function GetList_SQL()Function GetList_SQL() As DataTable Dim db As Database = DatabaseFactory.CreateDatabase() Dim sqlCommand As String = "select * FROM province ORDER BY id desc" '要对数据源执行的 SQL 语句或存储过程。 Dim dbCommand As DbCommand = db.GetSqlStringCommand(sqlCommand) Return db.ExecuteDataSet(dbCommand).Tables(0) End Function '列表 Public Function GetList_Access()Function GetList_Access() As DataTable Dim db As Database = New GenericDatabase("Driver={Microsoft Access Driver (*.mdb)};Dbq=D:vs2005dbdb.mdb;Uid=sa;Pwd=sa;", OdbcFactory.Instance) Dim sqlCommand As String = "select * FROM province ORDER BY id desc" '要对数据源执行的 SQL 语句或存储过程。 Dim dbCommand As DbCommand = db.GetSqlStringCommand(sqlCommand) Return db.ExecuteDataSet(dbCommand).Tables(0) End Function以上代码不多，应该明白了吧，呵呵，只要把“dv = GetList_Access().DefaultView”换成“dv = GetList_SQL().DefaultView”即可换成了SQL的数据库了，简单吧。这里只给出一个思路，就看大家封装起来成更加简单易用的咯。