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POJPA - How to update a collection in a bi-directionnal OneToMany/ManyToOne relation
 

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    <p>I have an owner (Category) and a customer (Forum) entities designed this way:</p> <p><strong>Category</strong></p> <pre><code>... @OneToMany( fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "category" ) @OrderBy( "position" ) private List&lt;Forum&gt; forums; ... </code></pre> <p><strong>Forum</strong></p> <pre><code>... @ManyToOne @JoinColumn( name = "category" ) private Category category; private Integer position; ... </code></pre> <p>Somewhere in my webapp, I display the forums list, and I execute some business action on one of them, for example changing its position.</p> <p>My issue is that the change is well persisted in the database, but is <strong>not reflected on the OneToMany mapped collection</strong>. Thus when I refresh the page that displays the list, it doesn't show the new position but the previous one.</p> <p>The code I use to update an element's position is equivalent to a simple <code>em.merge( forum )</code>. I read in many topics that I should "manually manage" the bidirectionnal relationship, otherwise I would face this kind of issues. Here are my two questions :</p> <ul> <li>I tried on both EclipseLink and Hibernate, and while it works well with Hibernate (list is updated), it doens't in EclipseLink. Is it related to some caching mode difference?</li> <li>How should I manually notice my list that one of its element's property has changed (e.g. the position property of a forum in the forums list) ?</li> </ul> <p><strong>[EDIT] I read <a href="https://stackoverflow.com/questions/4416359/entitymanager-doesnt-see-changes-made-in-other-transactions?lq=1">this topic</a> and I feel my issue is related to my forum being updated by a different session from the one being used to fetch the list. Am I understanding it right? If yes, how to correctly manage that case?</strong></p>
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