Question

I am very unfamiliar with SQL/HQL , and am currently stuck with this ‘maybe’ simple problem :

I have two many-to-many Entities , with a relation table :

Car , CarProblem , and Problem .

One Car may have many Problems ,

One Problem may appear in many Cars,

CarProblem is the association table with other properties .

Now , I want to find Car(s) with specified Problem , how do I write such HQL ?
All ids are Long type .

I’ve tried a lot of join / inner-join combinations , but all in vain..

— updated :

Sorry , forget to mention :

Car has many CarProblem

Problem has many CarProblem

Car and Problem are not directly connected in Java Object.

— update , java code below —

@Entity
public class Car extends Model{
  @OneToMany(mappedBy="car" , cascade=CascadeType.ALL)
  public Set<CarProblem> carProblems;
}

@Entity
public class CarProblem extends Model{
  @ManyToOne
  public Car car;      
  @ManyToOne
  public Problem problem;    
  ... other properties
}


@Entity
public class Problem extends Model  {
  other properties ...
  // not link to CarProblem , It seems not related to this problem

  // **This is a very stupid query , I want to get rid of it ...**
  public List<Car> findCars()
  {
    List<CarProblem> list = CarProblem.find("from CarProblem as cp where cp.problem.id = ? ", id).fetch();
    Set<Car> result = new HashSet<Car>();
    for(CarProblem cp : list)
      result.add(cp.car);

    return new ArrayList<Car>(result);
  }
}

The Model is from Play! framework , so these properties are all public .

Answer 1

I would question the need for the CarProblem altogether, but if you are going to keep this mapping I believe you could do something like this:

select c from CarProblem as cp join cp.car as c join cp.problem as p where p.id = :id