Entity Framework and SQL Server Savepoints

问题:

I asked a different question about Nested Transactions and the answer to my question educated me enough to help me realize I was asking the question poorly. So here's a better question.

How can I effectively implement SQL Server Savepoints (link 1, link 2) with a DAL built upon Entity Framework 4.0?

I would LIKE to write the following code and have it work in a way that SQL Server's SAVEPOINTS

public void Bar()
{
  using (var ts = new TransactionScope())
  {
    var ctx = new Context();
    DoSomeStuff(ctx);

    bool isSuccessful;

    using (var spA = new SavePoint("A")) // <-- this object doesn't really exist, I don't think
    {
      isSuccessful = DoSomeOtherStuff(ctx);
      if (isSuccessful)
        spA.Complete(); // else rollback bo prior to the beginning of this using block
    }

    Log(ctx, isSuccessful);

    ts.Complete();
  }
}

Is there such a way to do anything even close to resembling this, or something else that plays nicely with EF4? (we use custom self-tracking POCO entities)

回答1:

This isn't quite a full answer, but I suspect something like this might be going down the right path. My problem is that I'm not entirely sure how to get a SqlTransaction while in a TransactionScope.

/// <summary>
/// Makes a code block transactional in a way that can be partially rolled-back. This class cannot be inherited.
/// </summary>
/// <remarks>
/// This class makes use of SQL Server's SAVEPOINT feature, and requires an existing transaction.
/// If using TransactionScope, utilize the DependentTransaction class to obtain the current Transaction that this class requires.
/// </remarks>
public sealed class TransactionSavePoint : IDisposable
{
    public bool IsComplete { get; protected set; }
    internal SqlTransaction Transaction { get; set; }
    internal string SavePointName { get; set; }

    private readonly List<ConnectionState> _validConnectionStates = new List<ConnectionState>
                                                                        {
                                                                            ConnectionState.Open
                                                                        };

    public TransactionSavePoint(SqlTransaction transaction, string savePointName)
    {
        IsComplete = false;
        Transaction = transaction;
        SavePointName = savePointName;

        if (!_validConnectionStates.Contains(Transaction.Connection.State))
        {
            throw new ApplicationException("Invalid connection state: " + Transaction.Connection.State);
        }

        Transaction.Save(SavePointName);
    }

    /// <summary>
    /// Indicates that all operations within the savepoint are completed successfully.
    /// </summary>
    public void Complete()
    {
        IsComplete = true;
    }

    /// <summary>
    /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
    /// </summary>
    public void Dispose()
    {
        if (!IsComplete)
        {
            Transaction.Rollback(SavePointName);
        }
    }
}

This would be consumed as such, very similarly to a TransactionScope:

SqlTransaction myTransaction = Foo();

using (var tsp = new TransactionSavePoint(myTransaction , "SavePointName"))
{
  try
  {
    DoStuff();
    tsp.Complete
  }
  catch (Exception err)
  {
    LogError(err);
  }
}