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POget next sequence value from database using hibernate
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copied!<p>I have an entity that has an NON-ID field that must be set from a sequence. Currently, I fetch for the first value of the sequence, store it on the client's side, and compute from that value. </p> <p>However, I'm looking for a "better" way of doing this. I have implemented a way to fetch the next sequence value:</p> <pre><code>public Long getNextKey() { Query query = session.createSQLQuery( "select nextval('mySequence')" ); Long key = ((BigInteger) query.uniqueResult()).longValue(); return key; } </code></pre> <p>However, this way reduces the performance significantly (creation of ~5000 objects gets slowed down by a factor of 3 - from 5740ms to 13648ms ).</p> <p>I have tried to add a "fake" entity:</p> <pre><code>@Entity @SequenceGenerator(name = "sequence", sequenceName = "mySequence") public class SequenceFetcher { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "sequence") private long id; public long getId() { return id; } } </code></pre> <p>However this approach didn't work either (all the Ids returned were 0).</p> <p>Can someone advise me how to fetch the next sequence value using Hibernate efficiently?</p> <p><strong>Edit:</strong> Upon investigation, I have discovered that calling <code>Query query = session.createSQLQuery( "select nextval('mySequence')" );</code> is by far more inefficient than using the <code>@GeneratedValue</code>- because of Hibernate <strong>somehow</strong> manages to reduce the number of fetches when accessing the sequence described by <code>@GeneratedValue</code>. </p> <p>For example, when I create 70,000 entities, (thus with 70,000 primary keys fetched from the same sequence), I get everything I need.</p> <p><strong>HOWEVER</strong> , Hibernate only issues <strong>1404</strong> <code>select nextval ('local_key_sequence')</code> commands. NOTE: On the database side, the caching is set to 1.</p> <p>If I try to fetch all the data manually, it will take me 70,000 selects, thus a huge difference in performance. Does anyone know the internal functioning of Hibernate, and how to reproduce it manually?</p>

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