Design Problem: Object reference another object at different states

Question

Hi,
This is a problem I came across today while developing a simple prototype. Imagine I have a class Boy which has a one-to-many relation with a class Dog.
The class Boy has the following methods: getName(), setName(), getAge(), setAge(), getDogs().
The class Dog has the following methods: getName(), getOwner()
When the application starts I load a Boy from the database as follows:
Boy peter = BoyFactory.loadBoyByName("Peter");
peter.setAge(10);
I then add peter to a static list which can be accessed from everywhere within my application.
At a different stage in the application I want to load a dog (just a dog). So I use the following code:
Dog dog = DogFactory.loadDogByOwnerName("Peter");
The dog object (using JDO or Hibernate) would also have a reference to the Boy object. However when calling the getOwner() method, the boy returned will not be the same boy stored in that static list (I expect the age, which was not persisted in the database, to be different).
Is there a way how when loading the Dog object, since its Owner of type Boy is already loaded in my object model, a Framework such as Hibernate or JDO will use this object rather then re-build a new one.
I am planning to use either Hibernate or some JDO framework and that is why I am asking this question.
If I where going to use some custom made way to load Dog then I would just search if the Owner was in that static list and if yes then set the owner of the dog equal to the object found in the static list.
However I was wondering if there is some design I should consider (study) to handle such a problem.
Thanks and Regards,
Sim085

Answer 1

Thanks uj :) I had another thought...
I will give another scenario so things are more clear.
Imagine having a class Teacher which has one-to-many relation with a class Student.
If you where programming the classes for these two entities then would you program the student class as follows:class Student{
Teacher t = null;
void setTeacher(Teacher t){...}
Teacher getTeacher(){...}
}ORclass Student{
int teacherId = -1;
void setTeacherId(int tId){...}
int getTeacherId(){...}
}The difference between these two methods is that in the first method, if I wanted to know the teacher of a student then I would only have to call the getTeacher() method while using the second design I would first need to get the teacher Id and then make a database call to actually get the Teacher object (or else get it from a static list where the teacher could be saved.
Personally I prefer the first method since I like to have an object model where objects are directly linked with other rather then linked through some form of id. However I do not know which design is best to use...
Thanks
Sim085