在使用SqlCommand对象过程中，我们需要分配Connection对象。 通常，对于大型的Entity业务模型来说分配新的SqlConnection的操作非常频繁。要利用Pool的优化功能,就要想到保持Connection对象。由此想到可以把Connection和Transaction都保存到ConnectionProxy对象中。而此对象继承IDisposable仅仅存在于一个Request过程中。作为一个适用广泛的模型，我们建立ExecutionContext对象来封装对ConnectionProxy操作。
以下是ConnectionProxy代码：
internal class ConnectionProxy : IDisposable
...{
private string _connectionString = null;
private SqlConnection _connection;
private SqlTransaction _transaction;
private int _tranCount = 0;
/**//// <summary>
/// Constructs a new ConnectionProxy instance, setting the connection string
/// </summary>
/// <param name="ConnectionString">A valid database connection string</param>
internal ConnectionProxy(string connectionString)
...{
_connectionString = connectionString;
}
/**//// <summary>
/// Frees any connection related resources
/// </summary>
public void Dispose()
...{
// ensure that the connection does not have a pending transaction
if (_tranCount != 0)
...{
// rollback the transaction stack until the rollback already occurs
while (_tranCount > 0) this.RollbackTransaction();
throw new DataAccessException("Dispose was called on a connection with a pending transaction. The transaction will be aborted.");
}
// close the connection if it is open
if ((_connection != null) && (_connection.State == ConnectionState.Open))
...{
_connection.Close();
}
_connection = null;
}
/**//// <summary>
/// Gets the current connection object
/// </summary>
internal SqlConnection Connection
...{
get
...{
// check that the connection string property has been set
if (_connectionString == null)
...{
//throw new DataAccessException("Connection string has not been set.");
}
// create new connection and open if one does not yet exist
if (_connection == null)
...{
_connection = new SqlConnection(_connectionString);
_connection.Open();
//while (_connection.State == ConnectionState.Open) ;
}
return _connection;
}
}
/**//// <summary>
/// Gets the current transaction context object
/// </summary>
internal SqlTransaction Transaction
...{
get
...{
return _transaction;
}
}
/**//// <summary>
/// Begins a new transaction
/// </summary>
internal void BeginTransaction()
...{
// only actually begin a new transaction if a transaction context does not yet exist
if (_tranCount == 0)
...{
// create new transaction context at the specified isolation level
_transaction = Connection.BeginTransaction(IsolationLevel.Serializable);
}
_tranCount++;
}
/**//// <summary>
/// Commits a pending transaction
/// </summary>
internal void CommitTransaction()
...{
// check that a transaction context actually exists
if (_tranCount <= 0) throw new DataAccessException("No transaction is pending");
_tranCount--;
// check if an actual commit should occur
if (_tranCount == 0)
...{
// if trancount is zero, but we don't have a transaction then something is wrong
if (_transaction == null)
...{
throw (new DataAccessException("Transaction stack indicated a commit but no transaction exists!"));
}
// actually commit the transaction
_transaction.Commit();
_transaction = null;
}
}
/**//// <summary>
/// Rolls back a pending transaction
/// </summary>
internal void RollbackTransaction()
...{
// check that a transaction context actually exists
if (_tranCount <= 0) throw new DataAccessException("No transaction is pending");
_tranCount--;
// check if an actual rollback should occur
if (_tranCount == 0)
...{
// if trancount is zero, but we don't have a transaction then something is wrong
if (_transaction == null)
...{
throw (new DataAccessException("Transaction stack indicated a rollback but no transaction exists!"));
}
// actually rollback the transaction
_transaction.Rollback();
_transaction = null;
}
}
}
之后我们可以建立ExecutionContext.目的是使用这个Proxy.当然也可以保存和使用其他的实例化对象：
public sealed class ExecutionContext
...{
private static string ConnProxy = "ConnProxy";
private static string ConfigProxy = "Config";
private static ConnectionProxy _ConnProxy;
private static Config _Config;
/**//// <summary>
/// This class cannot be instantiated
/// </summary>
private ExecutionContext()
...{
}
/**//// <summary>
///
/// </summary>
private static ConnectionProxy ConnectionProxy
...{
get
...{
if (HttpContext.Current != null) //web app
return (ConnectionProxy)HttpContext.Current.Items[ConnProxy];
else
return _ConnProxy;
}
set
...{
if(HttpContext.Current != null) //web app
HttpContext.Current.Items.Add(ConnProxy, value);
else
_ConnProxy = value;
}
}
private static Config Config
...{
get
...{
if (HttpContext.Current != null) //web app
return (Config)HttpContext.Current.Items[ConfigProxy];
else
return _Config;
}
set
...{
if (HttpContext.Current != null) //web app
HttpContext.Current.Items.Add(ConfigProxy, value);
else
_Config = value;
}
}
/**//// <summary>
/// Returns the connection object for the current execution context
/// </summary>
public static SqlConnection Connection
...{
get
...{
AssertInitialisation();
return ConnectionProxy.Connection;
}
}
/**//// <summary>
/// Returns the current transaction object for the current execution context
/// </summary>
public static SqlTransaction Transaction
...{
get
...{
AssertInitialisation();
return ConnectionProxy.Transaction;
}
}
/**//// <summary>
/// </summary>
public static Config Configuration
...{
get
...{
if (Config == null)
throw new Exception("Config.xml cannot be loaded!");
return Config;
}
}
/**//// <summary>
/// Begins a new execution context
/// </summary>
public static void Begin()
...{
// cleanup from any previous Begin calls
End();
// create a configuration object
Config = new Config();
// create a new database connection proxy
ConnectionProxy = new ConnectionProxy(Config.ConnectionString);
}
/**//// <summary>
/// Ends the current execution context and cleans up any resources used
/// </summary>
public static void End()
...{
// clean up any objects that have not been cleaned up since the last Begin call on the thread
if (ConnectionProxy != null) ConnectionProxy.Dispose();
if (HttpContext.Current != null) //web app
...{
HttpContext.Current.Items.Remove(ConnProxy);
HttpContext.Current.Items.Remove(ConfigProxy);
}
}
/**//// <summary>
/// Begins a new transaction
/// </summary>
public static void BeginTransaction()
...{
AssertInitialisation();
ConnectionProxy.BeginTransaction();
}
/**//// <summary>
/// Commits the current transaction
/// </summary>
public static void CommitTransaction()
...{
AssertInitialisation();
ConnectionProxy.CommitTransaction();
}
/**//// <summary>
/// Rolls back the current transaction
/// </summary>
public static void RollbackTransaction()
...{
AssertInitialisation();
ConnectionProxy.RollbackTransaction();
}
/**//// <summary>
/// Asserts that the execution context has been correctly initialised
/// </summary>
private static void AssertInitialisation()
...{
if (ConnectionProxy == null)
...{
throw new ExecutionContextException("Execution Context has not been initialised.");
}
}
}
使用的时候，要在Global.asax的Application_BeginRequest中加入：ExecutionContext.Begin();和Application_EndRequest中加入：ExecutionContext.End();也可以在WinForm程序的Application中加入这2行。
准备工作完成后我们就可以来测试了：
ExecutionContext.BeginTransaction();
try
...{
cmd.Connection = ExecutionContext.Connection;
cmd.Transaction = ExecutionContext.Transaction;
cmd.ExecuteNonQuery();
ExecutionContext.CommitTransaction();
}
catch
...{
ExecutionContext.RollbackTransaction();
throw;
}
总结：
非常有效的数据库/配置文件访问模型。成功使用在几万流量的网站上。任何建议欢迎大家交流。
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