Question

Normally to realized linked objects, i usually use getter and setter methods and this way i add objects of different type to another object.

Now i have come across this Ruby Structure, e.g:

class Article < ActiveRecord::Base 
  has_many :comments 
end 
class Comments < ActiveRecord::Base 
  belongs_to :article 
end  

Can you tell me what is the equivalent of this has_many and belongs_to in Java. Basically i want to translate some similar data structure from Ruby to Java.

Answer 1

Highly depends on the ORM you’re using. Most (I assume) people will go with Hibernate in java. With Hibernate you have the possibility to annotate relationships quite similar.

@OneToMany and @ManyToOne annotations seem to be those which you might have to take a closer look at.

Article class:

public class Article {
    @OneToMany(mappedBy = "belongsTo")
    private List<Comment> comments;
    [...]
}

Comment class:

public class Comment {
    @ManyToOne
    private Article belongsTo;
    [...]
}

If you want to use another ORM, I’m afraid I can’t help you out 🙂