ClassCastException trying to cast retrieved JPA object to concrete class

Question

I am not certain what I am doing wrong, but I have a class that has a class within it, so when I save the Skill class the user class also gets created, so when I do the join and I want to pull everything in at one time, I get a classcastexception.

This is how I am calling my query.

val retrieved_obj = em.createNamedQuery("findAllSkillsByUser").setParameter("username", user.username ).getResultList().asInstanceOf[java.util.List[Skill]]
assertEquals(1, retrieved_obj.size())
val retrieved = retrieved_obj.get(0).asInstanceOf[Skill]

This is my query: <query><![CDATA[from Skill a JOIN a.user u WHERE u.username=:username]]></query>

This is what hibernate is actually doing in my test:

Hibernate: insert into users (firstName, lastName, username, id) values (?, ?, ?, ?)
Hibernate: insert into skills (datestarted, name, position, rating, skill_user_fk, id) values (?, ?, ?, ?, ?, ?)
Hibernate: select skill0_.id as id64_0_, user1_.id as id63_1_, skill0_.datestarted as datestar2_64_0_, skill0_.name as name64_0_, skill0_.position as position64_0_, skill0_.rating as rating64_0_, skill0_.skill_user_fk as skill6_64_0_, user1_.firstName as firstName63_1_, user1_.lastName as lastName63_1_, user1_.username as username63_1_ from skills skill0_ inner join users user1_ on skill0_.skill_user_fk=user1_.id where user1_.username=?

I expect the problem is all the user1 parts in the select.

The Skill class just has some setters/getters, basically, so I removed most of the annotations but the foreign key one:

  var id : Int = _
  var name : String = ""
  var position : Int = _
  var dateStarted : Date = new Date()
  var rating : SkillRating.Value = SkillRating.unknown

  @OneToOne{val fetch = FetchType.EAGER, val cascade=Array(CascadeType.PERSIST, CascadeType.REMOVE)}
  @JoinColumn{val name = "skill_user_fk", val nullable = false}
  var user : User = _

This is the User class:

  var id : Int = _
  var firstName : String = ""
  var lastName : String = ""
  var username : String = ""

This is my error:

java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to jblack.resumeapp.lift.model.Skill

I would rather no just select the Skill attributes and then have to do another query for the user, as that will be less efficient as my classes get more complicated.

Answer 1

You're selecting both Skill and User and getting back an object array containing both as elements.

You can either treat it as such or rewrite your query a bit:

select a from Skill a JOIN FETCH a.user u WHERE u.username=:username

to select only Skill but fetch and populate its User association.