Is a entity class can return some other entity instance in OOAD?

Question

I have two classes:

public class Car
{
    private int id;
    private String name;
    private String vendor;

    /* ... */
}

public class Garage 
{
    private int id;
    private String name;
    private String address;

    /* get-set and others stuffs */

    public boolean addCar(Car c) {
        /*
            This will insert a car to tblCars
            but belong to this garage
        */
    }

    public List<Car> getListCar {
        /* 
            This will perform a SELECT query on tblCars
            to choose cars belong to this Garage
        */
    }
}

Is it allowed in OOAD?

duffymo · Answer 1 · 2013-05-03T13:07:35.633

1

Allowed? What do you think is going to happen - an OOAD cop pull you over to the side and give you a ticket?

You can do anything you want. You'll find out if it's misguided after the fact.

Your design looks acceptable, except the Garage does not have a Collection<Car>.

This is a one-to-many relationship between Car and Garage. That's how it's usually done.

I think the Smalltalk MVC ideas are a little outdated. Here's how I see layers for a web app:

view-->controller-->service--+-->persistence
                             |
                             +--> model

Controller and view and tightly coupled together.

The service is the thing that knows about DAOs and model objects. They fulfill use cases and own units of work.

edited May 03 '13 at 13:07

answered May 03 '13 at 12:57

duffymo

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Thanks, I mean, for example, in 3-tier design pattern, Presentation layer shouldn't make a direct call to Data Access Layer but throught a Control layer, so, are these any rules that prohibit one entity call/access/return to other entites? – Bình Nguyên May 03 '13 at 13:01
view should have no reference to controller (in MVC). The arrow should be from controller to view. – Oliver Watkins May 03 '13 at 13:14
It's intended to show info flow, not dependency – duffymo May 03 '13 at 13:56

score 1 · Answer 2 · answered May 03 '13 at 13:11

It all depends on your requirements. If you are required to save a car every time it goes into a garage then use a delegate to handle the DB insert :

public boolean addCar(Car c) {
    Delegate.getInstance().addCarToGarage(this, c);
}

public List<Car> getListCar {
    Delegate.getInstance().getAllCars();
}

Otherwise just leave it as

public boolean addCar(Car c) {
    myCarList.add(c);
}

public List<Car> getListCar {
    return myCarList();
}

And save it at some other point.

Is a entity class can return some other entity instance in OOAD?

2 Answers2