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POjpa criteria query duplicate values in fetched list
 

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  1. POjpa criteria query duplicate values in fetched list
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    <p>I'm observing what I think is an unexpected behaviour in JPA 2 when fetching a list attribute with a criteria query.</p> <p>My query is as follows (an extract of it):</p> <pre class="lang-java prettyprint-override"><code>CriteriaBuilder b = em.getCriteriaBuilder(); CriteriaQuery&lt;MainObject&gt; c = b.createQuery(MainObject.class); Root&lt;MainObject&gt; root = c.from(MainObject.class); Join&lt;MainObject, FirstFetch&gt; firstFetch = (Join&lt;MainObject, FirstFetch&gt;) root.fetch(MainObject_.firstFetch); firstFetch.fetch(FirstFetch_.secondFetch); //secondFetch is a list c.select(root).distinct(true); </code></pre> <p>(So let's say I'm fetching a list as a property of the property of an object.)</p> <p>The thing is when the query returns multiple results, secondFetch values are duplicated as many times as rows are returned. Each <em>firstFetch</em> should have just one <em>secondFetch</em> but has <strong>n</strong> instead. The only particularity i see in this case is all <em>MainObjects</em> happen to have the same FirstFetch instance. So my guess is the join is being crossed, which is normal, but then JPA fails to assign its <em>secondFetch</em> object to each one of the <em>firstFetchs</em>.</p> <p>Mappings shouldn't be too special, the're more or less like this</p> <pre class="lang-java prettyprint-override"><code>@Entity @Table(name="mainobject") public class MainObject{ //... private FirstFetch firstFetch; @ManyToOne(fetch=FetchType.LAZY) @JoinColumn(name="mainObject_column") public FirstFetch getFirstFetch() { return firstFetch; } } </code></pre> <p>and</p> <pre class="lang-java prettyprint-override"><code>@Entity @Table(name="firstFetch") public class FirstFetch{ //... private List&lt;SecondFetch&gt; secondFetch; @OneToMany(mappedBy="secondFetch") public List&lt;SecondFetch&gt; getSecondFetch() { return secondFetch; } } </code></pre> <p>&amp; finally</p> <pre class="lang-java prettyprint-override"><code>@Entity @Table(name="secondFetch") public class SecondFetch { //.... private FirstFetch firstFetch; //bidirectional @ManyToOne @JoinColumn(name="column") public FirstFetch getFirstFetch() { return firstFetch; } } </code></pre> <p>I've been looking for some sort of <strong>distinct</strong> sentence to apply to the fetch but there's none (would have been a 'patch' anyway...)</p> <p>If i change</p> <pre class="lang-java prettyprint-override"><code>List&lt;SecondFetch&gt; </code></pre> <p>for</p> <pre class="lang-java prettyprint-override"><code>Set&lt;SecondFetch&gt; </code></pre> <p>i'll get the expected result thanks to Sets' <strong>Keys</strong>, so I do feel this is kind of a misbehaviour in JPA's lists.</p> <p>I'm not an expert, though, so i could perfectlly be making some mistake in the mappings or query. Any feeback is very welcome to help clear this out. Thanks.</p>
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    1. COWhat JPA provider are you using? Could be a bug.
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      1. USJames
    2. COi'm using JBoss 6.1.0's default provider, which would be Hibernate 3.6.6 Final, if i'm not wrong.
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    3. COI'm having the exact same problem. I'm using criteria api to fetch the (second) list like this: d.fetch(FirstFetch_.secondFetch, JoinType.LEFT);
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      1. USJens
 

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