Re: [hibernate-dev] Mapping defaults for @OneToOne
In both of the following cases, Hibernate creates a unique key constraint:
1) <many-to-one name="employee" column="employee_id"
unique="true" not-null="true" />
2) <many-to-one name="employee" column="employee_id"
unique="true" not-null="false" />
The documentation is clear that setting unique="true" indicates that a unique
key constraint should be created.
I only see mappings for <many-to-one ... unique="true"
not-null="true" > in the documentation.
Is the combination in 2) valid (unique="true" not-null="false")?
----- Original Message -----
From: "Gail Badner" <gbadner(a)redhat.com>
To: "hibernate-dev" <hibernate-dev(a)lists.jboss.org>
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
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