CODEWITHSUNDEEP
javahibernatelistgenerics
Koray Tugay
Koray Tugay

Reputation: 23800

Hibernate class cast exception with Lists

So I have this code:

public List<FooRequirement> findByFoo(Foo foo) {
    return getCurrentSession().createQuery("select distinct fr.foo from FooBarRequirement fr where fr.Foo.id = :FooId")
            .setParameter("FooId", foo.getId()).list();
}

I call this code somewhere in my code with

List<FooRequirement> myList = dao.findByFoo(foo);

Then I got a ClassCastException and wondered what I was doing wrong. I debugged my code and I have seen that my list (myList) which is supposed to hold references of type FooRequirement objects is actually filled with references of type Foo.

Then I found my mistake: 

return getCurrentSession().createQuery("select distinct fr from FooBarRequirement fr where fr.Foo.id = :FooId"

There was a "select distinct fr.foo" but it should have been a "select distinct fr..." because I want a List of FooRequirements not Foos.

My question is, how did that reference made itself into the List in the first place? I mean how is it possible for a List to hold a foo ?

Some information about the classes:

All of the classes are entities, the db has tables for them.

Foo class has a field id and a description.

FooRequirement class is an ABSTRACT class and has a reference to Foo (ManyToOne), and id. FooRequirement DOES NOT extend Foo.

FooBarRequirement class extends a FooRequirement class, if it is relavent. It has a field Baz. (ManyToOne)

I hope the question is clear. Actually the situation was a bit more complicated but I tried making it as simple as possible.

Upvotes: 0

Views: 144

Answers (1)

kostja
kostja

Reputation: 61548

You are explicitly selecting Foo objects in your query select distinct fr.foo...

So this is the type that ends up in your List.

EDIT: You have defined the List you want to have as List<FooRequirement>. However the result list you get from the Session is not typed and thus can hold any Object, in your instance - Foo.

Since you cannot get a TypedQuery from a Hibernate Session, you might consider using the EntityManager interface.

Upvotes: 2

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