General or specific DAO to record delivery with information from multiple tables?

Question

I am creating a web application that lets the user store and retrieve information from a DB through a GUI using spring and hibernate.

I have gotten stuck when it comes to creating the DAO and service layer. I want to create a method that can add a new delivery. In my delivery table i have Product Id and Customer Id which both are mapped to their own tables that contain Product Name, Product Type and Customer Name, Customer Country respectively.

The part that I have trouble with is that I want the end user to record a delivery by entering the product type, product name, customer name, customer country and date . Do I,

(1) Create a DAO with a method for adding a new delivery that includes these objects

or

(2) Create a DAO that just persist a general object to the DB and then use a service method to implement the DAO for each separate object?

Thank you for your help!

/D

Answer 1

here is a snippet of my generic dao, which I inject into each service layer class.

@Component("Dao")
public class Dao implements IDao  {
    @Resource(name = "sessionFactory")
    private SessionFactory sessionFactory;

    @Override
    public <T> T save(final T o){
        return (T) sessionFactory.getCurrentSession().save(o);
    }

    @Override
    public void delete(final Object object) {
        sessionFactory.getCurrentSession().delete(object);
    }

    @Override
    public <T> T get(final Class<T> type, final Long id) {
        return (T) sessionFactory.getCurrentSession().get(type, id);
    }

    @Override
    public <T> List<T> getFieldsEq(final Class<T> type, final Map<String, Object> restrictions) {
        final Session session = sessionFactory.getCurrentSession();
        final Criteria crit = session.createCriteria(type);
        for (Map.Entry<String, Object> entry : restrictions.entrySet()) {
            crit.add(Restrictions.eq(entry.getKey(), entry.getValue()));
        }

        return crit.list();
    }
}

Which can hen be used in your service layer like so :

@Transactional(readOnly = true)
public List<City> getCities() {
  return dao.getAll(City.class);
}

And of course you could extend the dao for specific complex queries. Having one generic dao obeys single point of responsibility principle , DRY , and makes it easier to test. The transactions should be on serivce layer and directly relate to units of work.