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POJPA - Paginated query with ManyToMany collection returns wrong number of entities
 

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    <p>I have these two entities (here are simplified versions) :</p> <p>Topic : </p> <pre><code>@Entity public class Topic implements Serializable { @Id @GeneratedValue( strategy = GenerationType.IDENTITY ) private Long id; @ManyToMany @JoinTable( name = "topic_member", joinColumns = @JoinColumn( name = "topic" ), inverseJoinColumns = @JoinColumn( name = "member" ) ) @JoinFetch private List&lt;Member&gt; participants = new ArrayList&lt;Member&gt;(); ... </code></pre> <p>Member :</p> <pre><code>@Entity public class Member implements Serializable { @Id @GeneratedValue( strategy = GenerationType.IDENTITY ) private Long id; ... </code></pre> <p>Those are related through a join table <code>topic_member(member, topic)</code>, via a unidirectionnal @ManyToMany relationship.</p> <p>Everything works just fine when I insert stuff, no problem here.</p> <p>But when I want to select stuff, it becomes more tricky. Let's say I want to select all the topics related to a particular member. I wrote the following JPQL query:</p> <pre><code>SELECT t FROM Topic t WHERE :member MEMBER OF t.participants ORDER BY t.id DESC </code></pre> <p>And then I wrote this:</p> <pre><code>TypedQuery&lt;Topic&gt; query = em.createQuery( MY_JPQL_REQUEST, Topic.class ); query.setParameter( PARAM_MEMBER, member ); return query.getResultList(); </code></pre> <p>And it works just fine.</p> <p>But something is very weirdly wrong : it seems I can't use pagination on this query! For example, when I try this:</p> <pre><code>TypedQuery&lt;Topic&gt; query = em.createQuery( MY_JPQL_REQUEST, Topic.class ); query.setParameter( PARAM_MEMBER, member ); query.setFirstResult( 0 ); query.setMaxResults( 5 ); return query.getResultList(); </code></pre> <p>It returns me a wrong number of entities. For example, when the previous one returns 5, it returns only 3...</p> <p>What am I missing here? I can't understand what could go wrong.</p> <p>I've read <a href="http://www.eclipse.org/forums/index.php/t/321611/" rel="nofollow">this page</a> and I think there may be something here, but I can't figure out what.</p> <p><strong>[Edit] Here is what I have in the join table in the DB, if it helps:</strong></p> <pre> +-------------+--------------+ | member | topic | +-------------+--------------+ | 1 | 1 | | 1 | 2 | | 1 | 3 | | 1 | 4 | | 1 | 5 | | 2 | 1 | | 2 | 2 | | 2 | 3 | | 2 | 4 | | 2 | 5 | +-------------+--------------+ </pre> <p><strong>[Solution] Thanks to Chris, I got it working. I had to replace <code>@JoinFetch</code> by <code>@BatchFetch( BatchFetchType.JOIN )</code> on the <code>@ManyToMany</code> field, and to query <code>SELECT DISTINCT(t) FROM ...</code> instead of <code>SELECT t FROM ...</code>.</strong></p>
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