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
<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
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
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
本文转自lihuijun51CTO博客，原文链接：
http://blog.51cto.com/terrylee/67623
，如需转载请自行联系原作者
