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POHow does one gracefully merge object graphs after NHibernate StaleObjectStateException?
 

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    <p>We are trying to combine objects after a StaleObjectStateException has been thrown to save a merged copy.</p> <p>Here's our environmental situation:</p> <ul> <li>List item</li> <li>Multi-user system</li> <li>WPF Desktop application, SQL Server 2008 database</li> <li>NHibernate 3.1.0.4000, FluentNHibernate 1.2.0.712</li> <li>Global, long-running NHibernate sessions [for the moment. We understand session-per-presenter is the recommended pattern, but do not have time in our project schedule to convert at present.]</li> <li>Top-down saves and property navigation (that is to say we save the top-level object (herein called Parent) in our domain graph) </li> <li>.Cascade.AllDeleteOrphan() used in most cases.</li> <li>Users exclusively own some objects in the domain graph, but share ownership of the Parent.</li> <li>Navigation properties on Children objects do not exist.</li> <li>All classes have numeric ID and numeric Version fields.</li> </ul> <p>Use case:</p> <ul> <li>User 1 starts application and opens Parent.</li> <li>User 2 starts application and opens Parent.</li> <li>User 2 adds a child (herein C2).</li> <li>User 2 saves Parent.</li> <li>User 1 adds a child (herein C1).</li> <li>User 1 saves Parent.</li> <li>User 1 receives a StaleObjectStateException (and rightly so)</li> </ul> <p>We want to <em>gracefully</em> handle the exception. Because the users share ownership of the parent, User 1 should be able to save successfully, and save the Parent with both his new child, and User 2's child.</p> <p>When SOSE is thrown, according to Ayende (<a href="http://msdn.microsoft.com/en-us/magazine/ee819139.aspx" rel="nofollow noreferrer">http://msdn.microsoft.com/en-us/magazine/ee819139.aspx</a>):</p> <blockquote> <p>your session and its loaded entities are toast, because with NHibernate, an exception thrown from a session moves that session into an undefined state. You can no longer use that session or any loaded entities</p> </blockquote> <p>C1 has already been assigned an ID and Version # by the now-not-useful session. (I wish it had not been.)</p> <p>How do we combine the use of ISession.Merge() and ISession.Refresh() to get a newly saved Parent that has both C1 and C2 ?</p> <p>We have tried a number of arcane permutations, none of which fully work. Usually, either a "row was updated or deleted by another transaction (or unsaved-value mapping was incorrect" or an actual ID collision at the ODBC level.</p> <p>Our theory, at the moment:</p> <ol> <li>Reset version numbers on C1 (to prevent "unsaved-value mapping was incorrect")</li> <li>Get a new session</li> <li>newSession.Refresh(C1);</li> <li>newParent = newSession.QueryOver[...]</li> <li>newParent.Add(C1);</li> <li>newSession.SaveOrUpdate(newParent)</li> </ol> <p>However, all the documentation suggests that newSession.Merge is <em>supposed</em> to be sufficient.</p> <p>Other posts used as research: <BR/><a href="https://stackoverflow.com/questions/5611830/fluent-nhibernate-newbie-row-was-updated-or-deleted-by-another-transaction">Fluent NHibernate Newbie: Row was updated or deleted by another transaction</a> <BR/><a href="https://stackoverflow.com/questions/6845815/is-there-an-alternative-to-isession-merge-that-doesnt-throw-when-using-optimi">Is there an alternative to ISession.Merge() that doesn&#39;t throw when using optimistic locking?</a> <BR/><a href="https://stackoverflow.com/questions/3158491/staleobjectstateexception-row-was-updated-or-deleted-by">StaleObjectstateException row was updated or deleted by</a> <BR/><a href="https://stackoverflow.com/questions/6268249/how-i-can-tell-nhibernate-to-save-only-changed-properties">How I can tell NHibernate to save only changed properties</a> <BR/><a href="https://stackoverflow.com/questions/4838786/hibernate-jpa-how-to-handle-staleobjectstateexception-when-several-object-has">Hibernate (JPA): how to handle StaleObjectStateException when several object has been modified and commited</a> (java, but relevant, i think)</p>
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