Question

I have a hibernate DAO that is throwing a “failed to lazily initialize a collection of role” Exception when trying to access a member of the returned object that is a bag/Collection.

I understand the scope of the problem throwing the exception. Hibernate returns my object, and for any Collections, returns proxy objects. In my caller, when I go to access those proxy objects, because the hibernate session has expired, this exception is thrown.

What I want to know is, how can I keep the session from expiring using annotations? Is it possible?

For instance if my calling method is:

@RequestMapping("refresh.url")
public ModelAndView refresh(HttpServletRequest request, HttpServletResponse response, int id) throws Exception {
    TestObject myObj = testObjDao.get(id);
    // throws the exception
    myObj.getCollection();

How would I prevent this exception using annotations? I know one solution would be to extend the hibernate session via a callback which in pseudocode might look something like:

@RequestMapping("refresh.url")
public ModelAndView refresh(HttpServletRequest request, HttpServletResponse response, int id) throws Exception {
    session = get hibernate session...
    session.doInSession(new SessionCallback() {
        TestObject myObj = testObjDao.get(id);
        // no longer throws the exception
        myObj.getCollection();
    });

but this seems rather repetitive to have in all of my functions that need to access collections. isn’t there a way to simply slap an @Transactional annotation on there and be done with it? as in:

@RequestMapping("refresh.url")
@Transactional  // this doesn't extend the session to this method?
public ModelAndView refresh(HttpServletRequest request, HttpServletResponse response, int id) throws Exception {
    TestObject myObj = testObjDao.get(id);
    // throws the exception
    myObj.getCollection();

thanks for your help in explaining this to me.

Answer 1

The solution I used was to use the @LazyCollection annotation on the collection in the DAO.

@OneToMany(mappedBy = "<something here>", cascade = CascadeType.ALL)
@LazyCollection(LazyCollectionOption.FALSE)