The books that I've read regarding hibernate are, at best, reference tomes. They very seldom have good code examples, so I tend to use online resources for those needs.

However, I've always had a problem understanding the basic idea of hibernate persistence. I've read the books and understand the concepts, but in practice, I often see results that I don't understand. Perhaps you all can help, as you have in the past.

Let's look at a simple example of a dog and a cat that are friends. This isn't a rare occurrence. It also has the benefit of being much more interesting than my business case.

We want a function called "saveFriends" that takes a dog name and a cat name. We'll save the Dog and then the Cat. For this example to work, the cat is going to have a reference back to the dog. I understand this isn't an ideal example, but it's cute and works for our purposes.

FriendService.java

public int saveFriends(String dogName, String catName) {
    Dog fido = new Dog();
    Cat felix = new Cat();

    fido.name = dogName;
    fido = animalDao.saveDog(fido);

    felix.name = catName;
    [ex.A]felix.friend = fido;
    [ex.B]felix.friend = animalDao.getDogByName(dogName);
    animalDao.saveCat(felix);
}

AnimalDao.java (extends HibernateDaoSupport)

public Dog saveDog(Dog dog) {
    getHibernateTemplate().saveOrUpdate(dog);
    return dog
}

public Cat saveCat(Cat cat) {
    getHibernateTemplate().saveOrUpdate(cat);
    return cat;
}

public Dog getDogByName(String name) {
    return (Dog) getHibernateTemplate().find("from Dog where name=?", name).get(0);
}

Now, assume for a minute that I would like to use either example A or example B to save my friend. Is one better than the other to use?

I'll understand if neither of those examples work, but please explain why.