org.hibernate.WrongClassException on saving an entity via Hibernate

Question

In this question I am working with Hibernate 4.3.4.Final and Spring ORM 4.1.2.RELEASE.

I have an User class, that holds a Set of CardInstances like this:

Answer 1

I solved the problem.

The root cause lies in this design:

@Table
@Entity
@Inheritance
@DiscriminatorColumn(name = "card_type", discriminatorType = DiscriminatorType.STRING)
public class CardInstance {  
    protected T card;
}

@Entity
@DiscriminatorValue("leader")
public class LeaderCardInstance extends CardInstance {
}

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At runtime information about generic types of an class are not present in java. Refer to this question for further information: Java generics - type erasure - when and what happens

This means hibernate has no way of determining the actual type of the CardInstance class.

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The solution to this is simply getting rid of the generic type and all extending (implementing) classes and just use one class like this:

@Table
@Entity
@Inheritance
@DiscriminatorColumn(name = "card_type", discriminatorType = DiscriminatorType.STRING)
public class CardInstance {
    Card card;
}

This is possible (and by the way the better design) because the member card carries all the information about the card type.

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I hope this helps folk if they run into the same problem.