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POIs there a way in Hibernate to obtain an entity's loaded PersistentCollection without loading the entire entity object first?
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copied!<p>This is a puzzler! :D</p> <p>Is there a way to force Hibernate to load a collection for an entity without loading the entire entity first?</p> <p>Let m explain better. I have a Role entity annotated this way:</p> <pre><code>@Entity(name="Role") @Table(name = "ROLES") @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS) @javax.persistence.TableGenerator( name="GENERATED_IDS", table="GENERATED_IDS", valueColumnName = "ID" ) public abstract class Role implements Serializable { private static final long serialVersionUID = 1L; /** * The id of this role. Internal use only. * * @since 1.0 */ @Id @GeneratedValue(strategy = GenerationType.TABLE, generator="GENERATED_IDS") @Column(name = "ROLE_ID") protected long id; /** * Set of permissions granted to this role. * * @since 1.0 */ @OneToMany(cascade = { CascadeType.PERSIST, CascadeType.MERGE }, mappedBy="sourceRole") protected Set<Permission> permissions = new HashSet<Permission>(); ... } </code></pre> <p>When I access the permissions collection by doing:</p> <pre><code>Role role = ... Set permissions = role.getPermission(); </code></pre> <p>Hibernate wraps the returned collection with one of its subclasses of PersistentCollection. I can then use Hibernate.initialize(permissions); to force the collection to be initialized.</p> <p>However, what I need is a way to accomplish the same without first loading the role entity. I know the id for the entity I need the permissions collections for, and the Role for the collection (temp.pack.Role.permissions). </p> <p>Is there a way to do that? I wold like to avoid hitting the database to retrieve all fields of the Role object (many!) just to get the collection and discard them all.</p> <p>I could use a join, but that givens me access to the permission objects themselves, not the actual PersistentCollection wrapper which the one I need.</p> <p>I tried this:</p> <pre><code>Session session = connectionInfoProvider.getSession(); // this is just "permissions", the collection field name String attributeName = role.substring(role.lastIndexOf(".")+1, role.length()); // this is the Role class name, temp.pack.Role String entityClassName = role.substring(0, role.lastIndexOf(".")); Class<?> roleClass = Class.forName(entityClassName); Field collectionField = roleClass.getDeclaredField(attributeName); collectionField.setAccessible(true); Hibernate.initialize(collection); </code></pre> <p>But didn't work. The collection I get is just a regular empty set and nothing is loaded.</p> <p>I also tried this:</p> <pre><code>Session session = connectionInfoProvider.getSession(); // this is just "permissions", the collection field name String attributeName = role.substring(role.lastIndexOf(".")+1, role.length()); // this is the Role class name, temp.pack.Role String entityClassName = role.substring(0, role.lastIndexOf(".")); Class<?> roleClass = Class.forName(entityClassName); Field collectionField = roleClass.getDeclaredField(attributeName); collectionField.setAccessible(true); Object object = session.load(roleClass, id); ProxyObject objectProxy = (ProxyObject)object; LazyInitializer lazyInitializer = (LazyInitializer)objectProxy.getHandler(); Object objectImpl = lazyInitializer.getImplementation(); Object collection = collectionField.get(objectImpl); Hibernate.initialize(collection); </code></pre> <p>But also didn't work, it fails with <code>java.lang.IllegalArgumentException: unknown handler key</code>.</p> <p>I also tried:</p> <pre><code>PersistenceContext context = ((SessionImplementor)currSession).getPersistenceContext(); CollectionPersister persister = ((SessionFactoryImplementor) sessFactory) .getCollectionPersister(role); CollectionKey key = new CollectionKey(persister, id, EntityMode.POJO); // collection - contains set containing actual data PersistentCollection collection = context.getCollection(key); </code></pre> <p>But also fails with <code>java.lang.IllegalArgumentException: unknown handler key</code></p> <p>Any ideas on how to accomplish this?</p>

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