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copied!<p>I've been struggling with this for a while now. Am going to have another crack at it.</p> <p>I want to implement transactions in individual service containers - because that makes them self-contained - but then be able to nest a bunch of those service methods within a larger transaction and rollback the whole lot if necessary.</p> <p>Because I'm using <a href="http://www.ayende.com/Wiki/Rhino+Commons.ashx" rel="nofollow noreferrer">Rhino Commons</a> I'm now going to try refactoring using the <a href="https://rhino-tools.svn.sourceforge.net/svnroot/rhino-tools/trunk/commons/Rhino.Commons.NHibernate/With/With.Transaction.cs" rel="nofollow noreferrer"><code>With.Transaction</code></a> method. Basically it allows us to write code as if transactions were nested, though in reality there is only one.</p> <p>For example:</p> <pre><code>private Project CreateProject(string name) { var project = new Project(name); With.Transaction(delegate { UnitOfWork.CurrentSession.Save(project); }); return project; } private Sample CreateSample(Project project, string code) { var sample = new Sample(project, code); With.Transaction(delegate { UnitOfWork.CurrentSession.Save(sample); }); return sample; } private void Test_NoNestedTransaction() { var project = CreateProject("Project 1"); } private void TestNestedTransaction() { using (var tx = UnitOfWork.Current.BeginTransaction()) { try { var project = CreateProject("Project 6"); var sample = CreateSample(project, "SAMPLE006", true); } catch { tx.Rollback(); throw; } tx.Commit(); } } </code></pre> <p>In <code>Test_NoNestedTransaction()</code>, we are creating a project alone, without the context of a larger transaction. In this case, in <code>CreateSample</code> a new transaction will be created and committed, or rolled back if an exception occurs.</p> <p>In <code>Test_NestedTransaction()</code>, we are creating both a sample and a project. If anything goes wrong, we want both to be rolled back. In reality, the code in <code>CreateSample</code> and <code>CreateProject</code> will run just as if there were no transactions at all; it is entirely the outer transaction that decides whether to rollback or commit, and does so based on whether an exception is thrown. Really that's why I'm using a manually created transaction for the outer transaction; so we I have control over whether to commit or rollback, rather than just defaulting to <em>on-exception-rollback-else-commit</em>.</p> <p>You could achieve the same thing without Rhino.Commons by putting a whole lot of this sort of thing through your code:</p> <pre><code>if (!UnitOfWork.Current.IsInActiveTransaction) { tx = UnitOfWork.Current.BeginTransaction(); } _auditRepository.SaveNew(auditEvent); if (tx != null) { tx.Commit(); } </code></pre> <p>... and so on. But <code>With.Transaction</code>, despite the clunkiness of needing to create anonymous delegates, does that quite conveniently.</p> <p>An advantage of this approach over using <code>TransactionScope</code>s (apart from the reliance on MSDTC) is that there ought to be just a single flush to the database in the final outer-transaction commit, regardless of how many methods have been called in-between. In other words, we don't need to write uncommitted data to the database as we go, we're always just writing it to the local NHibernate cache.</p> <p>In short, this solution doesn't offer ultimate control over your transactions, because it doesn't ever use more than one transaction. I guess I can accept that, since nested transactions are by no means universally supported in every DBMS anyway. But now perhaps I can at least write code without worrying about whether we're already in a transaction or not.</p>

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