Enterprise Library2.0（1）：Data Access Application Block学习

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。