JPA Hibernate One-to-One relationship

Question

I have a one-to-one relationship but hibernatetool complains when generating the schema. Here's an example that shows the problem:

@Entity public class Person {     @Id     public int id;      @OneToOne     public OtherInfo otherInfo;      rest of attributes ... } 

Person has a one-to-one relationship with OtherInfo:

@Entity public class OtherInfo {     @Id     @OneToOne(mappedBy="otherInfo")     public Person person;      rest of attributes ... } 

Person is owning side of OtherInfo. OtherInfo is the owned side so person uses mappedBy to specify the attribute name "otherInfo" in Person.

I get the following error when using hibernatetool to generate the database schema:

org.hibernate.MappingException: Could not determine type for: Person, at table: OtherInfo, for columns: [org.hibernate.mapping.Column(person)]         at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:292)         at org.hibernate.mapping.SimpleValue.createIdentifierGenerator(SimpleValue.java:175)         at org.hibernate.cfg.Configuration.iterateGenerators(Configuration.java:743)         at org.hibernate.cfg.Configuration.generateDropSchemaScript(Configuration.java:854)         at org.hibernate.tool.hbm2ddl.SchemaExport.<init>(SchemaExport.java:128)         ... 

Any idea why? Am I a doing something wrong or is this a Hibernate bug?

Answer 1

JPA doesn't allow the @Id annotation on a OneToOne or ManyToOne mapping. What you are trying to do is one-to-one entity association with shared primary key. The simplest case is unidirectional one-to-one with shared key:

@Entity public class Person {     @Id     private int id;      @OneToOne     @PrimaryKeyJoinColumn     private OtherInfo otherInfo;      rest of attributes ... } 

The main problem with this is that JPA provides no support for shared primary key generation in OtherInfo entity. The classic book Java Persistence with Hibernate by Bauer and King gives the following solution to the problem using Hibernate extension:

@Entity public class OtherInfo {     @Id @GeneratedValue(generator = "customForeignGenerator")     @org.hibernate.annotations.GenericGenerator(         name = "customForeignGenerator",         strategy = "foreign",         parameters = @Parameter(name = "property", value = "person")     )     private Long id;      @OneToOne(mappedBy="otherInfo")     @PrimaryKeyJoinColumn     public Person person;      rest of attributes ... } 

Also, see here.

Answer 2

This should be working too using JPA 2.0 @MapsId annotation instead of Hibernate's GenericGenerator:

@Entity public class Person {      @Id     @GeneratedValue     public int id;      @OneToOne     @PrimaryKeyJoinColumn     public OtherInfo otherInfo;      rest of attributes ... }  @Entity public class OtherInfo {      @Id     public int id;      @MapsId     @OneToOne     @JoinColumn(name="id")     public Person person;      rest of attributes ... } 

More details on this in Hibernate 4.1 documentation under section 5.1.2.2.7.