Following on from a previous thread, I'm trying to understand the apparent inconsistency in Hibernate's outer-join behaviour between <one-to-one> and <many-to-one> associations.

Take the following mapping:

<class name="Parent" table="PARENT">
........
<!--
<one-to-one name="child" class="Child"/>
<many-to-one name="child" class="Child" column="CHILD_ID"/>
-->
</class>

If I uncomment the <one-to-one>, then run the query:

session.find(from Parent");

then Hibernate will not include Child in an outer join. However, if I use the <many-to-one> approach, then Hibernate will fetch Parent and Child together in a single outer join.

I can override this by using FETCH in the query, of course, but I'm trying to change the default behaviour so that the <one-to-one> is fetched in the same way as the <many-to-one>. Why do they behave differently?