JPQL: Problem with the following WHERE-Clause using Inheritance

Question

I'm using the following query, for getting all Fruits that are linked with the User.

return (List<Fruit>) getEm()
            .createQuery(
                    "SELECT DISTINCT f FROM Fruit f, User u WHERE (f = u.apples OR f = u.oranges OR f = u.mangos) AND u.id = :id")
            .setParameter("id", id).getResultList();

The corresponding Entities are the following:

public class Fruit{

private int id;

}

public class User{

private int id;
private Collection<Apple> apples;
private Collection<Orange> oranges;
private Collection<Mango> mangos;

}

public class Mango extends Fruit{

private int id;
...

}

public class Apple extends Fruit{

private int id;
...

}

public class Orange extends Fruit{

private int id;
...

}

The problem is, that the above mentioned query dont give me a result if any of the Collections dont exist for the user. So if a user has no apples, i dont get 0 as the result. I already tried to catch errors with statements like u.apples IS NOT EMPTY, etc. but it doenst work either.

So, could you give me a tipp for this case? The whole thing would be easier, if the Fruit would have a one-to-many relation to the user, but unfortunatelly i cant afford this for the program...

Thanks in advance!

Answer 1

Your JPQL is not valid, so I'm not sure how it works at all.

You can only use the "." notation on a ToOne not a ToMany, for a ToMany you need to use a join. For a join you can use an outer join to allow none.

SELECT DISTINCT f FROM Fruit f, User u left join u.apples a ... WHERE f = a or ...

Answer 2

怀疑您想输入IN而不是=，但是诸如“不能为程序提供此功能”之类的短语让我感到紧张，因为有很多被黑的东西在发生。