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POJPA EclipseLink @ElementCollection join fetch via CriteriaQuery
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copied!<p>I have an entity (Book) with an ElementCollection for a List property (tags).</p> <pre><code>@Entity @Table(name = "BOOK") public class Book { @ElementCollection(fetch = FetchType.EAGER) @CollectionTable(name = "BOOK_TAGS", joinColumns = @JoinColumn(name = "BOOK_ID")) @Column(name = "TAG", length = "4000") private List<String> tags; } </code></pre> <p>For getting a single book, I'm doing entityManager.find and for getting all the books, I'm doing criteria query. This all works. I now want to make the list of tags lazily loaded, which will prevent them from loading when I get all books (which I want) but I still want to load them when I get a particular Book.</p> <p>My first attempt is to change the entityManager.find to a query. The following works:</p> <pre><code>select b from Book b left outer join fetch b.tags where b.id = :id </code></pre> <p>However, I want to do this as a CriteriaQuery as well as add the option for getting tags on the get all books query. Doing the following is not working:</p> <pre><code>CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery cq = cb.createQuery(Book.class); Root<Book> b = cq.from(Book.class); b.fetch("tags", JoinType.LEFT); cq.select(b); cq.where(cb.equal(b.get("id"),cb.parameter(String.class,"id")); TypedQuery<Book> q = em.createQuery(cq); q.setParameter(id); return q.getSingleResult(); </code></pre> <p>This is failing in that it is not a single result - its looking like N objects where N is the number of tags.</p> <p>I also tried adding:</p> <pre><code>q.setHint("eclipselink.join-fetch","b.tags"); </code></pre> <p>and taking out the fetch but that also doesn't work.</p> <p>I'm getting the columns added to the SQL but its like the processing of those extra columns is messing up the returned object - its either multiples or no object (for hints).</p> <p>Any ideas how to turn the JOIN FETCH into a proper CriteriaQuery?</p>

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