Projections for Collections and Nested Projections

Question

Hi, The first part is HOW TO PROJECT COLLECTIONS?

Can We apply projections on collection elements? For e.g

    class User{
    private address List<Address>;
}

class Address{
    private String city;
    private String state;
}

Now can I just load the address attribute of User class? Using code like :

criteria.setProjection(Projections.property("Address"));

But it always return me null, even when the object does have an address field set. Is there any different way to project Collection Items??

THE SECOND PART : NESTED PROJECTIONS. Consider the same model as shown above, but instead of having a collection of Address, there is an single element. Now What if I want to just load the "city" attribute of Address which is an part of User class??

I tried doing :

Projections.property("Address.City")

But it gives me error, stating could not resolve property: "Address.City" of User.

Is there any provision for Projecting Collection elements and Nested Projections??

Answer 1

Hibernate is case sensitive. so instead of *A*ddress.*C*ity, use *a*ddress.*c*ity. If it does not work, try to use alias, like :

DetachedCriteria criteria = DetachedCriteria.forClass(User.class);
criteria.createAlias("address", "addAlias");
criteria.setProjection(Projections.property("addAlias.city"));