What would be the best practice to implement the following situation with Hibernate.
We define an abstract class that will form the base of any object that we want to persist in our database. It contains the id etc etc...
public abstract class ModelObject {
protected int id;
...
}
Now we subclass our base clase for special cases where more than one entity will have a similar fields.
public abstract class ModelObjectWithNose extends ModelObject {
...
protected Nose nose;
}
Now, for all classes that we want to have a Nose
:
public class Person extends ModelObjectWithNose { ... }
public class Animal extends ModelObjectWithNose { ... }
The real problem we have at the moment now is that this relationship needs to be bi-directional. Each concrete class needs to know which Nose
is theirs, but each Nose
also needs to know to what object it belongs.
public class Nose {
...
private ModelObjectWithNose owner;
}
For our example we need a @OneToOne
relationship, as each Person
can only have one Nose
and each Nose
can only belong to one Person
.
What we have tried is doing the following:
@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public abstract class ModelObjectWithNose extend ModelObject { ... }
and then:
@Entity
public class Person extends ModelObjectWithNose { ... }
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...etc etc etc.
1) How do I define the relationship between the Nose
and the ModelObjectWithNose
? Is it as simple as:
@Entity
public class Nose {
...
// this causes: 'Basic' attribute should not be 'Persistence Entity'
ModelObjectWithNose owner;
}
2) Is there a better / more preferred way? Would the inheritance strategy work properly?
Thanks!
EDIT
So I have tried a few ways which all seem to potentially work. Using any of the three Inheritance schemes works fine if you set up the annotations as in the question. Unfortunately this has a huge impact on our existing database and code, so we opted to (for now) simply index the Nose
object's id
field that is kept on our current objects that would have extended ModelObjectWithNose
and simply write helper methods to do point queries to find the entries.
Annotate your Nose
property in ModelObjectWithNose
as @OneToOne
and in the Nose
entity you do the same with ModelObjectWithNose owner
. Set the mappedBy
attribute of the annotation of the Nose
entity, so JPA knows on which table the FK should be inserted (In your model the ModelObjectWithNose
should have the FK to Nose
, not other way around. You set it on the inverse end of the one-to-one relationship, ie. the one that has the PK to use.)
BTW your Entities must implement Serializable
(you can do so on the ModelObject
class to enforce it on inheriting classes). The id
property of ModelObject
should be annotated as @Id
.
Cheers, Kai
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