我正在使用Linq to SQL连接到大约2000个数据库之一的ASP.NET MVC应用程序。我们注意到，该应用程序花费大量时间到数据库的连接我们的分析工具，而且我怀疑这是部分原因是由于连接池碎片如下所述：http://msdn.microsoft.com/en-us/library/8xx3tyca(v=vs.110).aspxLINQ to Sql：更改每个连接的数据库
Many Internet service providers host several Web sites on a single server. They may use a single database to confirm a Forms authentication login and then open a connection to a specific database for that user or group of users. The connection to the authentication database is pooled and used by everyone. However, there is a separate pool of connections to each database, which increase the number of connections to the server.
There is a relatively simple way to avoid this side effect without compromising security when you connect to SQL Server. Instead of connecting to a separate database for each user or group, connect to the same database on the server and then execute the Transact-SQL USE statement to change to the desired database.
我想实现这个解决方案在Linq to Sql中，所以我们有更少的开放连接，所以当我们需要时，更有可能在池中有可用的连接。为此，我需要在Linq每次尝试运行查询时更改数据库。有没有什么办法可以在不重构整个应用程序的情况下完成这个任务？目前，我们只是为每个请求创建一个数据上下文，并且该数据上下文可能会打开和关闭多个连接。每次打开连接时，我都需要告诉它要使用哪个数据库。
我当前的解决方案或多或少像this one - 它将SqlConnection对象封装在继承自DbConnection的类中。这允许我重写Open（）方法并在打开连接时更改数据库。它适用于大多数情况下确定的，但在这使得许多更新的请求，我得到这个错误：
System.InvalidOperationException: Transaction does not match connection
我的想法是，我会再以同样的方式裹DbTransaction对象是什么我的SqlConnection一样，并确保其连接属性将指向包装的连接对象。修正了上述错误，但引入了一个新的DbCommand无法将我的包装连接强制转换为SqlConnection对象的新特性。于是我也包装了DbCommand，现在我得到了关于未初始化的DbCommand对象事务的新的令人兴奋的错误。
总之，我觉得我追逐的是具体的错误，而不是真正理解正在发生的事情。我是否在这个包装战略的正确轨道上，还是有更好的解决方案，我错过了？
这里是我的三个包装类的更有趣的部分：
public class ScaledSqlConnection : DbConnection
{
private string _dbName;
private SqlConnection _sc;
public override void Open()
{
//open the connection, change the database to the one that was passed in
_sc.Open();
if (this._dbName != null)
this.ChangeDatabase(this._dbName);
}
protected override DbTransaction BeginDbTransaction(IsolationLevel isolationLevel)
{
return new ScaledSqlTransaction(this, _sc.BeginTransaction(isolationLevel));
}
protected override DbCommand CreateDbCommand()
{
return new ScaledSqlCommand(_sc.CreateCommand(), this);
}
}
public class ScaledSqlTransaction : DbTransaction
{
private SqlTransaction _sqlTransaction = null;
private ScaledSqlConnection _conn = null;
protected override DbConnection DbConnection
{
get { return _conn; }
}
}
public class ScaledSqlCommand : DbCommand
{
private SqlCommand _cmd;
private ScaledSqlConnection _conn;
private ScaledSqlTransaction _transaction;
public ScaledSqlCommand(SqlCommand cmd, ScaledSqlConnection conn)
{
this._cmd = cmd;
this._conn = conn;
}
protected override DbConnection DbConnection
{
get
{
return _conn;
}
set
{
if (value is ScaledSqlConnection)
_conn = (ScaledSqlConnection)value;
else
throw new Exception("Only ScaledSqlConnections can be connections here.");
}
}
protected override DbTransaction DbTransaction
{
get
{
if (_transaction == null && _cmd.Transaction != null)
_transaction = new ScaledSqlTransaction(this._conn, _cmd.Transaction);
return _transaction;
}
set
{
if (value == null)
{
_transaction = null;
_cmd.Transaction = null;
}
else
{
if (value is ScaledSqlTransaction)
_transaction = (ScaledSqlTransaction)value;
else
throw new Exception("Don't set the transaction of a ScaledDbCommand with " + value.ToString());
}
}
}
}
}