JPA @OneToOne throws Error when mapped to an abstract @Entity with subclasses

Question

I have a problem when an Entity is mapped to another Entity which has a direct implementation on its subclasses. See sample mapping below:

@Entity
class Location {
      @OneToOne
      @JoinColumn(...)
      private Person person;
}

@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="person_type",discriminatorType=DiscriminatorType.STRING)
abstract class Person {
}

@Entity
@DiscriminatorValue("M")
class Man extends Person {
    ...
}

@Entity
@DiscriminatorValue("W")
class Woman extends Person {
    ...
}

Now, this is what I have on my database table:

location-table: id=1, person_id=1 person-table: id=1,person_type="M"

When I retrieve the Location using entity manager, hibernate throws an exception saying that i cannot instantiate an abstract class or an interface.

Location location = entityManager.find(Location.class, 1L);

Hibernate throws this error:

javax.persistence.PersistenceException: org.hibernate.InstantiationException: Cannot instantiate abstract class or interface: Person
at org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:630)
at org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:195)
at ......
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:59)
at org.junit.internal.runners.MethodRoadie.runTestMethod(MethodRoadie.java:98)
at org.unitils.UnitilsJUnit4TestClassRunner$TestListenerInvokingMethodRoadie.runTestMethod(UnitilsJUnit4TestClassRunner.java:174)
at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:79)
at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:87)
at org.unitils.UnitilsJUnit4TestClassRunner$TestListenerInvokingMethodRoadie.runBeforesThenTestThenAfters(UnitilsJUnit4TestClassRunner.java:156)
at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:77)
at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:42)
at org.unitils.UnitilsJUnit4TestClassRunner.invokeTestMethod(UnitilsJUnit4TestClassRunner.java:95)
at org.junit.internal.runners.JUnit4ClassRunner.runMethods(JUnit4ClassRunner.java:51)
at org.unitils.UnitilsJUnit4TestClassRunner.access$000(UnitilsJUnit4TestClassRunner.java:44)
at org.unitils.UnitilsJUnit4TestClassRunner$1.run(UnitilsJUnit4TestClassRunner.java:62)
at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:27)
at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:37)
at org.unitils.UnitilsJUnit4TestClassRunner.run(UnitilsJUnit4TestClassRunner.java:68)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:49)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

Answer 1

This did the trick for me, using hibernate as persistence provider.

@OneToOne(cascade = {CascadeType.PERSIST,CascadeType.MERGE}) 

Answer 2

From The Java EE 6 Tutorial - Entity Inheritence:

Any mapping or relationship annotations in non-entity superclasses are ignored.

So you seem to be correct that you have to annotate the Person class with @Entity to associate it with a Location via @OneToOne.

From the @MappedSuperclass javadoc

A class designated with the MappedSuperclass annotation can be mapped in the same way as an entity except that the mappings will apply only to its subclasses since no table exists for the mapped superclass itself.

So you couldn't use @MappedSuperclass on Person, then map it with the @OneToOne, since there would be no Person table.

Seems like the JPA annotations you are using are correct. Have you tried @Martin Klinke's suggestion of a dummy discriminator value for the Person class?