Data Access Application Block 提供了通用的数据访问的功能，随着 2.0 版本的推出有了很大变化。 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

Data Access Application Block提供了通用的数据访问的功能，随着2.0版本的推出有了很大变化。

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

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();