From: "Gail Badner" <gbadner(a)redhat.com&gt; To: "hibernate-dev" <hibernate-dev(a)lists.jboss.org&gt; Sent: Tuesday, December 2, 2014 9:34:24 PM Subject: [hibernate-dev] Mapping defaults for @OneToOne I'm a bit confused by the mapping defaults for @OneToOne defined in JPA 2.1. Sections 2.10.1 and 2.10.3.1 (Bidirectional and Unidirectional OneToOne Relationships) says, "The foreign key column has the same type as the primary key of table B and there is a unique key constraint on it." Section 11.1.41 (OneToOne Annotation) says that, by default, optional=true, which translates into nullable foreign key column(s). IIUC, the default mapping is not supported by many (all?) databases, because a constraint violation exception will be thrown if a column has a unique key constraint and there is more than one null value for that column. Currently, Hibernate does not create a unique key unless @OneToOne( optional=false ) is defined. I believe Hibernate is doing the right thing here, but it is not consistent with the spec. Is the spec wrong in this case, or am I missing something? Please let me know... Thanks, Gail _______________________________________________ hibernate-dev mailing list hibernate-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev