try/catch 块的收益回报

问题描述

正如 Eric Lippert 在 这篇文章，try/catch 子句中不允许yield return.

As Eric Lippert described in this article, yield return is not allowed within try/catch clauses.

有没有一种很好的方法可以让我得到这样的东西，而不必手动编写自己的IEnumerator:

Is there a nice way I could get something like this, without having to write my own IEnumerator by hand:

public IEnumerable<Data> GetData()
{
    var transaction = Session.BeginTransaction());
    try 
    {
        IQuery q = CreateQuery(session);

        foreach (var result in q.Enumerable())
            yield return ProjectResult(result);  // <-- doesn't work

        session.Commit();
    }
    catch (Exception ex)
    {
        transaction.Rollback();
        throw;
    }
    finally
    {
        transaction.Dispose();
    }
}

推荐答案

我只是像这样更改事务处理逻辑:

I'd just change the transaction-handling logic like this:

public IEnumerable<Data> GetData()
{
    var transaction = Session.BeginTransaction();
    bool rollback = true;
    try 
    {
        IQuery q = CreateQuery(session);

        foreach (var result in q.Enumerable())
        {
            yield return ProjectResult(result);
        }

        rollback = false;
        session.Commit();
    }
    finally
    {
        if (rollback)
        {
            transaction.Rollback();
        }
        transaction.Dispose();
    }
}

或者，如果您的事务支持除非已提交，否则处理意味着回滚"的想法:

Or if your transaction supports the idea of "dispose means rollback unless it's commited":

public IEnumerable<Data> GetData()
{
    using (var transaction = Session.BeginTransaction();
    {
        IQuery q = CreateQuery(session);

        foreach (var result in q.Enumerable())
        {
            yield return ProjectResult(result);
        }

        // Commits the tnrasaction, so disposing it won't roll it back.
        session.Commit();
    }
}