正确处理DbConnection

Question

我有一个包装DbConnection的名为DatabaseHelper的类。为using语句设置此类的正确方法是什么？我已经实现了IDisposible，但我不确定应该在何时何地调用Connection.Close()或Connection.Dispose()。

当我只是在自己的Dispose()方法中调用Connection.Dispose()时，有时会从我的DbConnection对象中获得一个SocketException。我认为这是因为旧的连接是开放的，但没有附加到异常的细节，所以我不能确定。

Answer 1

从dispose方法中调用connection.Dispose()。您应该看看实现IDisposable的标准模式，它超越了简单地实现IDisposable接口，并允许部署非托管对象等：

public void Dispose()
{
    Dispose(true);
    GC.SuppressFinalize(this);
}

protected virtual void Dispose(bool disposing)
{
    if (!disposed)
    {
        if (disposing)
        {
            // Dispose managed resources.
        }

        // There are no unmanaged resources to release, but
        // if we add them, they need to be released here.
    }
    disposed = true;

    // If it is available, make the call to the
    // base class's Dispose(Boolean) method
    base.Dispose(disposing);
}

(摘自http://msdn.microsoft.com/en-us/library/system.idisposable.aspx)。

Answer 2

据this新闻组报道：

下面是IDbConnection.Dispose()的实现方式(如反射器工具所示)：

SqlClient：

protected override void Dispose(bool disposing)
{
       if (disposing)
       {
             switch (this._objectState)
             {
                   case ConnectionState.Open:
                   {
                         this.Close();
                         break;
                   }
             }
             this._constr = null;
       }
       base.Dispose(disposing);
}

Odbc:
protected override void Dispose(bool disposing)
{
       if (disposing)
       {
             this._constr = null;
             this.Close();
             CNativeBuffer buffer1 = this._buffer;
             if (buffer1 != null)
             {
                   buffer1.Dispose();
                   this._buffer = null;
             }
       }
       base.Dispose(disposing);
}

OleDb:
protected override void Dispose(bool disposing)
{
       if (disposing)
       {
             if (this.objectState != 0)
             {
                   this.DisposeManaged();
                   if (base.DesignMode)
                   {
                         OleDbConnection.ReleaseObjectPool();
                   }
                   this.OnStateChange(ConnectionState.Open, ConnectionState.Closed);
             }
             if (this.propertyIDSet != null)
             {
                   this.propertyIDSet.Dispose();
                   this.propertyIDSet = null;
             }
             this._constr = null;
       }
       base.Dispose(disposing);
}

dispose方法应仅在连接处于打开状态时尝试关闭该连接。

Answer 3

这个析构函数语法实际上就是终结器。终结器正在调用Dispose(false)方法。

    #region IDisposable Members
    private bool _isDisposed;

    private void ThrowIfDisposed()
    {
        if (_isDisposed)
            throw new ObjectDisposedException(this.GetType().Name);
    }

    protected virtual void Dispose(bool disposing)
    {
        if (!_isDisposed)
        {
            if (disposing)
            {
                //part 1 : disposing managed objects
                _command.Dispose();
                _command.Connection.Dispose();
                if (_command.Transaction != null)
                    _command.Transaction.Dispose();
            }
            //part 2: disposing unmanged objects. Here there are no unmanged objects.
            _isDisposed = true;
        }
    }

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    //~DbCommandExecutor() //No need of finalize here. Because there is no unmanged objects in my class. ie, no code in part 2.
    //{
    //    Dispose(false);
    //}
    #endregion

直到你的代码有了第二部分的代码，才需要终结器(或析构函数)语法的。否则，为了安全起见，应该实现它。也就是说，即使程序员没有正确调用dispose方法，finalize也应该清理非托管资源。

比较示例:来自msdn

http://msdn.microsoft.com/en-us/library/system.idisposable.dispose.aspx和http://msdn.microsoft.com/en-us/library/fs2xkftw.aspx