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POMultiple fetches with EAGER type in Hibernate with JPA
 

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  1. POMultiple fetches with EAGER type in Hibernate with JPA
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    <p>I have an entity which contains:</p> <pre><code>@OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, mappedBy = "assessment") @OrderBy(value = "order ASC") private List&lt;AssessmentPart&gt; assessmentParts = new LinkedList&lt;&gt;(); @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, mappedBy = "assessment") private List&lt;AssessmentText&gt; texts = new LinkedList&lt;&gt;(); </code></pre> <p>as you see there are two collections which needs to be eagerly loaded. This is not working and hibernate throws an exception:</p> <pre><code>Caused by: org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags </code></pre> <p>That's because Hibernate can't fetch multiple collections with one go. But if I change the <code>List</code> to <code>Set</code> and the <code>LinkedList</code> to <code>HashSet</code> this part works fine but the other - more annoying issue occurs.</p> <p>When I am trying to get the entity from the database using:</p> <pre><code>entityManager.find(entityClass, primaryKey); </code></pre> <p>It fails with:</p> <pre><code>org.hibernate.AssertionFailure: null identifier </code></pre> <p>I am sure that ID I am passing to <code>find</code> method is not null, I've debugged and I am sure of this. It somehow disappears inside Hibernate.</p> <p>If I change collection types to <code>LAZY</code> everything just works without errors but there are some circumstances where I need to use <code>EAGER</code>.</p> <p>Does anybody have a solution how to fix it? Either I could have a set but prevent assertion error from occurring or I could have a list but somehow avoid multiple fetch bags error.</p> <p>I am using:</p> <pre><code>Hibernate 4.2.2.Final Tomcat 7 JPA 2.0 JDK 1.7 </code></pre> <p><strong>EDIT</strong></p> <p>I've just discovered that adding <code>@Fetch(FetchMode.SELECT)</code> fixes the issue and I can use multiple list with <code>EAGER</code> type, but is there anyway to solve this by not using Hibernate specific annotations? And why it fixed the issue in the first place?</p>
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