Issue with Hibernate Inheritance. Subclass using wrong sequence

Question

My mappings are below.

Here is the base class for all classes. There is no table for this class. All subclasses user id as their PK.

@MappedSuperclass
public abstract class Model {
    private Long id;

    @Id
    @GeneratedValue(strategy=GenerationType.Sequence, generator="myGenerator")
    public Long getId() { return id; }
}

A class for Comments that has its own table, with columns for all the fields in Model

@Entity
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
@Table(name = "COMMENT")
@SequenceGenerator(name="myGenerator", sequenceName="COMMENT_SEQ", allocationSize=1)
public class Comment extends Model {
    //some data
}

A subclass of Comment that also has its own table, with columns for all the fields in Comment and Model

@Entity
@Table(name = "ORDER_COMMENT")
@SequenceGenerator(name="myGenerator", sequenceName="ORDER_COMMENT_SEQ", allocationSize=1)
public class OrderComment extends Model {
    //some data
}

This class has its own table and can have one to many order comments.

@Entity
@Table(name="ORDER")
@SequenceGenerator(name="myGenerator", sequenceName="ORDER_SEQ", allocationSize=1)
public class Order extends Model {
    private Set<OrderComment> = new HashSet<OrderComment>();

    @OneToMany
    @JoinColumn(name="ORDER_ID")
    public Set<OrderComment> getComments() { return comments; }
}

The issue is that when I add a new OrderComment to an Order, Hibernate selects the id from the sequence for Comment instead of the sequence for OrderComment.

Any ideas on why this is happening and what I can change to fix this issue? Or is there a better way to map this?

Answer 1

A SequenceGenerator is globally identified by it's name, hence you can only have one called "myGenerator".

If you wish to use your identifier on a global variable, with @GeneratedValue, you'll need to define a single @SequenceGenerator and use a single sequence for all your tables.

Alternatively, you could keep an abstract getId method at your superclass and implement it on every subclass: hibernate is happy and you'll have a uniform way to reach your id's.

Answer 2

We use the sequence generator here to make each Model distinguishable, So a Comment is a Model , an OrderComment is a Model , an Order is a Model , too. They should share a sequence generator from this view.

You can define a single sequence generator used by multiple entities as this post .