In activeJDBC, how to enforce the presence of a one-to-many relationship to a model

Question

Assuming I have the following DB model:

Car(
  id             INT
  plaque_id      INT

)

Plaque(
  id             INT
  identification TEXT
)

So in ActiveJDBC, my models are:

public class Car extends Model {

    static{
        validatePresenceOf("plaque_id");
    }

    public Car () {}
}

..

public class Plaque extends Model {

        static{
            validatePresenceOf("identification");
        }

        public Car () {}
    }

Assuming my specification says: a car must have a plaque.

As you can see, I am enforcing the presence of plaque_id to the Car model.

Now. When I try this:

Car model_s = new Car();
Plaque plaque_a = new Plaque();

plaque_a.set("identification","A-8000");
plaque_a.saveIt();

car.add(plaque_a);
car.saveIt();

I got the following exception thrown:

java.lang.IllegalArgumentException: You can only add associated model to an instance that exists in DB. Save this instance first, then you will be able to add dependencies to it.

If I understand correctly, my car model_s must be saved first before being able to link plaque plaque_a. But I cannot save model_s without a plaque due to my validation rule. It's a catch-22.

Note: I am new to activeJDBC.

score 0 · Accepted Answer · answered Apr 10 '17 at 03:59

I think you got it backwards. Since your table Car has a column plaque_id, it means that a Plaque has many Car(s), which is a One-to-Many association: http://javalite.io/one_to_many_associations.

Therefore, you need to add Car to Plaque, and not the other way around:

Car model_s = new Car();    // set parameters on the car
plaque_a.set("identification","A-8000");
plaque_a.saveIt();
plaque_a.add(model_s);

Other recommendations:

1) In Java, use CamelCase: modelS, not model_s

2) Add constructor to Plaque:

public class Plaque{
   public Plaque(String identification){ 
      set("identification", identification);
   }
   public Plaque(){} // must have default constructor
}

then your code will look cleaner:

Car model_s = new Car();    // set parameters on the car
Plaque plaque = new Plaque("A-8000");
plaque_a.saveIt();
plaque_a.add(modelS);

Generally, try to avoid dynamic setters and getters, they are OK for a small project, but writing permanent setters and getters will get you an amazing power of Java refactoring, something you do not have in Ruby.

In activeJDBC, how to enforce the presence of a one-to-many relationship to a model

1 Answers1