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JPA 2.1 Specification (JSR-338 section 2.10.3.1 "Unidirectional OneToOne Relationshps") specifies:
"Table A conttains a foreign key to table B. The foreign key column name is formed as the concatenation of the following: the name of the realtionship property or field of entity A; "_"' the name of the primary key column in table B. The foreign key column has the same type as primary key of table B and there is a unique key constraint on it."
But Hibernate does not put unique constraint in such scenario.
First entity:
@Entity
public class FootballPlayer {
@Id
private long id;
@OneToOne
private Ball ball;
public FootballPlayer() {
}
public FootballPlayer(long id) { this.id = id; }
public long getId() { return id; }
public void setBall(Ball ball) { this.ball = ball; }
public Ball getBall() { return ball; }
}
Second entity:
@Entity
public class Ball {
@Id
private long id;
public Ball() {
}
public Ball(long id) { this.id = id; }
public long getId() { return id; }
}
Scenario:
EntityManagerFactory emf = Persistence.createEntityManagerFactory("pu");
EntityManager em = emf.createEntityManager();
FootballPlayer firstPlayer = new FootballPlayer(1L);
FootballPlayer secondPlayer = new FootballPlayer(2L);
Ball ball = new Ball(10L);
firstPlayer.setBall(ball);
secondPlayer.setBall(ball);
em.getTransaction().begin();
em.persist(ball);
em.persist(firstPlayer);
em.persist(secondPlayer);
em.getTransaction().commit();
em.close();
emf.close();
persistence unit configuration from persitence.xml:
<persistence-unit name="pu">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<class>com.mprzybylak.minefields.jpa.relationships.onetoone.uni.Ball</class>
<class>com.mprzybylak.minefields.jpa.relationships.onetoone.uni.FootballPlayer</class>
<properties>
<property name="javax.persistence.jdbc.driver" value="org.apache.derby.jdbc.EmbeddedDriver" />
<property name="javax.persistence.jdbc.url" value="jdbc:derby:memory:test;create=true" />
<property name="javax.persistence.jdbc.user" value="APP" />
<property name="javax.persistence.jdbc.password" value="APP" />
<property name="hibernate.show_sql" value="true" />
<property name="hibernate.use_sql_comments" value="true"/>
<property name="hibernate.hbm2ddl.auto" value="create" />
</properties>
</persistence-unit>
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