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POHow to handle EntityExistsException properly?
 

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    <p>I have two entities: Question and FavoritesCounter. FavoritesCounter should be created when the question is added to favorites for the first time. </p> <p>Consider a use case when two users tries to add a question to favorites simultaneously - this will cause <code>EntityExistsException</code> when <code>entityManager.persist(counter)</code> is called for the second user.</p> <p>But the code below <strong>doesn't work</strong>, because when <code>EntityExistsException</code> is thrown, container marks transaction as <em>rollback only</em> and attempt to return <code>getFavoritesCounter(question)</code> fails with <code>javax.resource.ResourceException: Transaction is not active</code></p> <pre><code>@Stateless public class FavoritesServiceBean implements FavoritesService { ... public void addToFavorites(Question question) { FavoritesCounter counter = getCounter(question); if (counter == null) { counter = createCounter(question); } //increase counter } private FavoritesCounter createCounter(Question question) { try { FavoritesCounter counter = new FavoritesCounter(); counter.setQuestion(question); entityManager.persist(counter); entityManager.flush(); return counter; } catch (EntityExistsException e) { return getFavoritesCounter(question); } } private FavoritesCounter getFavoritesCounter(Question question) { Query counterQuery = entityManager.createQery("SELECT counter FROM FavoritesCounter counter WHERE counter.question = :question"); counterQuery.setParameter("question", question); List&lt;FavoritesCounter&gt; result = counterQuery.getResultList(); if (result.isEmpty()) return null; return result.get(0); } } </code></pre> <p><strong>Question</strong></p> <pre><code>@Entity public class Question implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; //getter and setter for id } </code></pre> <p><strong>FavoritesCounter</strong></p> <pre><code>@Entity public class FavoritesCounter implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; @OneToOne @Column(unique = true) private Question question; //getter and setter } </code></pre> <p>What is the best way to return already created entity after <code>EntityExistsException</code>?</p>
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