ElementCollection createAlias in hibernate API

问题

does anyone know if and how the solution for following question (which is written in the JPA API) can be written using the hibernate criteria API?

To be more specific I have a Discussion entity that contains a list of participants (which is a list of usernames):

@ElementCollection
@Column(name = "user_name")
@CollectionTable(name = "DISCUSSION_USER", joinColumns = @JoinColumn(name = "DISCUSSION_ID"))
@OrderColumn(name = "ORDER_INDEX")
private List<String> participants = new ArrayList<String>();

Now I need to retrieve all Discussions where a given username is a participant.

If I would have created an entity for Participant this would be straightforward:

    Criteria crit = getSession().createCriteria(Discussion.class);
    crit.createAlias("participants", "p");
    crit.add(Restrictions.eq("p.userName", portalUsername));

But I can't create an alias with a non entity...

回答1:

Late answer.

The correct propertyName for collection (annotated by @ElementCollection) is "elements" or constant CollectionPropertyNames#COLLECTION_ELEMENTS.

Try with the following answers

Criteria crit = getSession().createCriteria(Discussion.class);
crit.createAlias("participants", "p");

crit.add(Restrictions.eq("p.elements", portalUsername));

or use the constant COLLECTION_ELEMENTS instead

crit.add(Restrictions.eq("p." + CollectionPropertyNames.COLLECTION_ELEMENTS, portalUsername));

回答2:

As explained here what I wanted is not possible:

The limitations of using an ElementCollection instead of a OneToMany is that the target objects cannot be queried, persisted, merged independently of their parent object. They are strictly privately-owned (dependent) objects, the same as an Embedded mapping. There is no cascade option on an ElementCollection, the target objects are always persisted, merged, removed with their parent.

So, I used a OneToMany instead.

回答3:

Can you give us a more complete schema and query?

Also, Criteria API sucks. Try using QueryDSL, your query might look like:

HibernateQuery q=new HibernateQuery(getSession())
.from(QDiscussion.discussion).from(QDocument.document)
.where(QDocument.document.userName.in(QDiscussion.discussion.userNames))
.list(QDocument.document);

来源：https://stackoverflow.com/questions/4873021/elementcollection-createalias-in-hibernate-api