JPA - Interface Entity

Question

Hi,
I am looking for help to create an class hierarchy that would use interface instead inheritance.
My example: In a house I have livingrooms, kitchens, and bedrooms. So I have a class for each type of room, and theses classes extends Contruction (another entity).
I also have furniture. I would like to retrieve all the rooms that have a funiture type.
See below (simple version):
@Entity
class Construction {
@Id
private Long id
@Entity
class LivingRoom extends Construction implements Equipable {
@ManyToMany
List<Funiture> furnitures
@Entity
class Furniture {
@ManyToMany
List<Equipable> equipables
}Is it possible to map that with JPA? My final objective is to retrieve a List of Places that a forniture could be, and also alll the forniture that a place could have.
I am trying that with jpa/hibernate but I am not having any success.
And, if it is not possible, the best way to implement that?
Thx

Answer 1

Unfortunately you cannot do this. From the persistence section of the JavaEE 5 Tutorial:
The persistent state of an entity can be accessed either through the entity�s
instance variables or through JavaBeans-style properties. The fields or properties
must be of the following Java language types:
� Java primitive types
� java.lang.String
� Other serializable types including:
� Wrappers of Java primitive types
� java.math.BigInteger
� java.math.BigDecimal
� java.util.Date
� java.util.Calendar
� java.sql.Date
� java.sql.Time
� java.sql.TimeStamp
� User-defined serializable types
� byte[]
� Byte[]
� char[]
� Character[]
� Enumerated types
� Other entities and/or collections of entities
� Embeddable classes
As you can see this doesn't mention interfaces, which makes sense since they are abstract and have no actual state to persist - the best way I've thought of to cope would be to have everything you want to implement 'equipable' inherit from a parent class, even if that class is completely anemic.
If anyone has any better solutions please reply.