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
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