Question

I have an entity A that has a collection of basic types (e.g. String). I use such a mapping because the strings associated to each instance of A depend on A‘s lifecycle. If I want to remove an instance of A from the DB, I also want its associated Strings to be removed.

My mapping is as follows:

@Entity
public class A {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(name = "name", nullable = false, unique = true)
    private String name;

    @ElementCollection(fetch = FetchType.EAGER)
    @CollectionTable(name = "AStrings", joinColumns = @JoinColumn(name = "id"))
    @Column(name = "strings", nullable = false)
    private Set<String> strings;
}

If I create an instance of A and add it some strings, then I can persist the instance using Session.save(myInstance). Both the instance of A and its associated Strings are persisted.

But, if I want to remove the same instance from the DB, using Session.createQuery("delete A a where a.name = ?").setString(0, name).executeUpdate(), I get a foreign key constraint error:

Cannot delete or update a parent row: a foreign key constraint fails

But, I would expect the associated Strings to be automatically removed before removing the A‘s instance, but it seems it’s not the case. I also didn’t found a way to specify cascade rules.

Is there something wrong with my configuration?

Thanks

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EDIT: I’ve also tried using @Cascade(CascadeType.DELETE) on the field strings, and it still doesn’t help. By looking at the database, I don’t see any ON DELETE policy for the concerned foreign key.

Someone who had the same issue opened a JIRA: https://hibernate.onjira.com/browse/HHH-4301. A solution (or workaround) has to exist, I can’t be the only person that uses @ElementCollection.

I’ve solved the issue. I thought that deleting using Session.delete() or using an HQL query was equivalent, but it seems not. Using HQL query, the dependent objects are not automatically deleted, so I get a foreign key constraint error. Using Session.delete() solves the problem. Also, Hibernate doesn’t seem to use cascade functionality of the DB since I still don’t see any CASCADE policy in the generated DDL, it handles this internally.

Answer 1

I’ve solved the issue.

I thought that deleting an Entity using Session.delete() or using an HQL query was equivalent, but it seems not. Using HQL query, the dependent objects are not automatically deleted, so I get a foreign key constraint error as explained in the question.

Using Session.delete() solves the problem. Also, Hibernate doesn’t seem to use cascade functionality of the DB since I still don’t see any CASCADE policy in the generated DDL, it handles this internally.

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For moderators:

I’ve added my answer to the question in the past (as you asked) but since this is the answer that solves the issue and that no answer (from other users) has been posted, I think I should post it here as an answer.