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How to persist a class which extends List<>? [message #1027145]

Tue, 26 March 2013 16:00

Jan Vleeshouwers

Messages: 2
Registered: March 2013

Junior Member

What annotations are necessary to persist a class which extends List<>?
For example:

@Entity
public class Walk extends ArrayList<Step> implements Serializable { ... }

with a straight entity class Step:

@Entity
public class Step implements Serializable { ... }

Both have simple auto-generated id fields and the appropriate equals() and hashCode() implementations.

I would like the following code to persist the walk including the inserted steps. The entity manager em is created from the factory.

Walk walk = new Walk();
walk.add(new Step());
walk.add(new Step());
walk.add(new Step());
em.getTransaction().begin();
em.persist(walk);
em.getTransaction().commit();

This persists the Walk object in a table which only has an ID-column. No Steps are persisted, nor any relationships. I would expect to need a @OneToMany annotation somewhere, to cascade the persist operation to the Step objects. But where?
Or am I trying to do something that is not possible?

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Re: How to persist a class which extends List<>? [message #1028744 is a reply to message #1027145]

Thu, 28 March 2013 17:21

Chris Delahunt

Messages: 1389
Registered: July 2009

Senior Member

It doesn't make sense from a JPA/entity point of view to extend a collection, and JPA cannot see any attributes internal to the ArrayList class to map to the database. Your Work entity needs an ID and a collection attribute holding Step entities. If you want to use work as a list or collection type, have it implement List and just wraps the step collection attribute.

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Re: How to persist a class which extends List<>? [message #1029233 is a reply to message #1028744]

Fri, 29 March 2013 10:58

Jan Vleeshouwers

Messages: 2
Registered: March 2013

Junior Member

So I was trying to do something impossible.
Your suggestion works, I already assumed that would be the alternative.
Thanks for the reply!

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