I’ve been searching a way to do a lazy a “one-to-zero-or-one”

relationship in Hibernate and I finally found a way to do it using

many-to-one with unique=”true”. See example below:

Association: Person [1 <--> 0..1] Note
<class name=”Person” table=”person”>

   <id name=”id” column=”id” type=”int” unsaved-value=”-1″>

       <generator class=”sequence”>

           <param name=”sequence”father_id_seq</param>

       </generator>

   </id>

   <property name=”name” type=”string”/>

   <many-to-one name=”note” class=”Note” column=”id” 

                unique=”true” insert=”false” update=”false”

                cascade=”all”/>

</class>
<class name=”Note” table=”note”>

   <id name=”id” column=”id” type=”int” unsaved-value=”-1″ >

       <generator class=”foreign”>

           <param name=”property”>owner</param>

       </generator>

   </id> 

   <property name=”note” type=”string”/>

   <one-to-one name=”owner” class=”Person” constrained=”true”/>

</class>

Observe that column “id” is used twice in Person mapping.I’ve been

searching a way to do a lazy a “one-to-zero-or-one” relationship in

Hibernate and I finally found a way to do it using many-to-one with

unique=”true”. See example below:
Association: Person [1 <--> 0..1] Note
<class name=”Person” table=”person”>

   <id name=”id” column=”id” type=”int” unsaved-value=”-1″>

       <generator class=”sequence”>

           <param name=”sequence”father_id_seq</param>

       </generator>

   </id>

   <property name=”name” type=”string”/>

   <many-to-one name=”note” class=”Note” column=”id” 

                unique=”true” insert=”false” update=”false”

                cascade=”all”/>

</class>
<class name=”Note” table=”note”>

   <id name=”id” column=”id” type=”int” unsaved-value=”-1″ >

       <generator class=”foreign”>

           <param name=”property”>owner</param>

       </generator>

   </id> 

   <property name=”note” type=”string”/>

   <one-to-one name=”owner” class=”Person” constrained=”true”/>

</class>

Observe that column “id” is used twice in Person mapping.