DAO classes, foreign key and join query

[giuseppe gio]

Hi to all, i need some suggestion for a DAO implementation of a database.
First question.
How i represent a foreign key into a dao class? for example, i have this two tables:

book(id, title, author)
author(name, age)

where book(author) is a foreign key on author(name)

Just i need to code foreign key as a String (in this case) like

public class BookDao {

    private int id;
    private String title;
    private String author;
    //rest of class implementation
}

Or is not a good practice?

Second question.
With dao i can do CRUD operations, but if i need to make a query that join two or more table, how can i do?

[Rob Spoor]

I'd use JPA, with Hibernate as implementation of choice in a JSE environment. That way, you can use annotations to mark the relationship, and JPA will do the rest for you. In your case your Book class would get a property of type Author.

Note however that what you've shown is not a DAO (data access object), but sooner an entity (in JPA terms) or DTO (data transfer object).

[S Majumder]

Ya I completely agree with Rob .
You can check this nice article : webpage

Thanks ,
Satya

[giuseppe gio]

Ops, sorry, i've made a mistake, it was a DTO representation.
I don't want to use a specific framework, i just want to understand some design principle, and then i'll use framework.
So into DTO class, foreign key it's something like

private Author author;

Now, when i need to do a query that need a join of two or more table, what's the best way to implement classes?

thanks for the answers.