I have a top level class where all OneToOne annotations have (fetch=FetchType.LAZY). This sort of works as advertised. Each association is populated by a separate query. Unfortunately the query is run for each top-level object loaded regardless of whether the associated property is accessed.

The following annotation in the Person class:

@OneToOne(
cascade = CascadeType.REMOVE,
fetch = FetchType.LAZY
)
@PrimaryKeyJoinColumn
private ContactInfo contactInfo;

Yields the following hibernate queries for Person and ContactInfo, even though ContactInfo hasn't been accessed.

Doing the same thing with ManyToOne (fetch=FetchType.LAZY) on other properties and it works as expected. The query is run only when the associated property is accessed.

Using Hibernate 3.1.2, EntityManager 3.1beta6, Annotations 3.1beta8.

Thank you. This makes perfect sense.

So in the terminology of annotations, adding "optional=false" to the OneToOne annotation will result in the true LAZY behavior, assuming the db relationship supports it.

I noticed that in the EJB3 spec, the default value of "optional" is true for both OneToOne and ManyToOne. I guess this means that even though the ManyToOne behavior is currently lazy without specifying optional=false, the optional=false should still be explicitly stated to ensure the same behavior in the future.

@OneToOne(fetch=LAZY, optional=true) @PKJC can be lazyfied depending on the actual implementation choice.
It's a tradeoff between field level interception and proxy based lazy loading.