Multiple writable mappings exception in EclipseLink - jpa

Question

I have these tables:
Which my intention is : A user can be a company or a person but each one of them have something in common, as username which is the email and password, so I used the JPA Tools to generate the entities from the table which result on this:
public class User implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
private int id;
private String email;
private String password;
private int reputation;
//bi-directional one-to-one association to Company
#OneToOne(mappedBy="user", cascade={CascadeType.ALL})
private Company company;
//bi-directional many-to-one association to Location
#OneToMany(mappedBy="user")
private List<Location> locations;
//bi-directional one-to-one association to Person
#OneToOne(mappedBy="user")
private Person person;
//bi-directional many-to-one association to Product
#OneToMany(mappedBy="user")
private List<Product> products;
//bi-directional many-to-one association to UserType
#ManyToOne
#JoinColumn(name="type")
private UserType userType;
//bi-directional many-to-one association to UserPhone
#OneToMany(mappedBy="user")
private List<UserPhone> userPhones;
//bi-directional many-to-one association to UserPicture
#OneToMany(mappedBy="user")
private List<UserPicture> userPictures;
//bi-directional many-to-one association to UserSocialNetwork
#OneToMany(mappedBy="user")
private List<UserSocialNetwork> userSocialNetworks;
// getter and setters
}
Now if I try to persist an user object launchs the follow exception in EclipseLink:
Exception [EclipseLink-48] (Eclipse Persistence Services - 2.3.0.v20110604-r9504): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: Multiple writable mappings exist for the field [COMPANY.id_user]. Only one may be defined as writable, all others must be specified read-only.
Mapping: org.eclipse.persistence.mappings.OneToOneMapping[user]
Descriptor: RelationalDescriptor(entity.Company --> [DatabaseTable(COMPANY)])
Exception [EclipseLink-48] (Eclipse Persistence Services - 2.3.0.v20110604-r9504): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: Multiple writable mappings exist for the field [PERSON.id_user]. Only one may be defined as writable, all others must be specified read-only.
Mapping: org.eclipse.persistence.mappings.OneToOneMapping[user]
Descriptor: RelationalDescriptor(entity.Person --> [DatabaseTable(PERSON)])
Runtime Exceptions:
Is the generated mapping wrong ?
How can I solve this exception ?
Update
public class Company implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
#Column(name="id_user")
private int idUser;
private String email;
private String name;
//bi-directional many-to-one association to Area
#ManyToOne
#JoinColumn(name="area")
private Area areaBean;
//bi-directional one-to-one association to User
#OneToOne(cascade={CascadeType.ALL})
#JoinColumn(name="id_user", insertable=false, updatable=false)
private User user;
// getter and setters
}
#Entity
public class Person implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
#Column(name="id_user")
private int idUser;
#Temporal( TemporalType.DATE)
private Date birthdate;
private String gender;
private String name;
private String surname;
//bi-directional one-to-one association to User
#OneToOne
#JoinColumn(name="id_user", insertable=false, updatable=false)
private User user;
// getters and setters
}

Answer 1

I solved my problem placing the insertable=false, updatable=false in the #JoinColumn annotation in both classes, Person and Company.

Answer 2

The proper way to do this is to use #PrimaryKeyJoinColumn instead of plain old #JoinColumn.
reference wiki example on PrimaryKeyJoinColumn

Answer 3

My guess is that you have the id_user mapped twice, once using a Basic #Id mapping, and once using the #ManyToOne. You need to make one of them read-only, i.e. insertable/updatable=false. Or better, just remove the basic id, and put the #Id on the #ManyToOne.
See,
http://en.wikibooks.org/wiki/Java_Persistence/Identity_and_Sequencing#Primary_Keys_through_OneToOne_and_ManyToOne_Relationships