OneToOne and LazyToOne

walterw · **Joined:** Thu Feb 21, 2008 3:31 pm **Posts:** 34

Hi all,

I have a mapping in a User domain class that has a OneToOne with another class. I want to only load this mapping when the getter is called.

I came across this mapping that should do that; however, when I query for the Object, it runs another query to populate the OneToOne mapping:

Code:

@OneToOne(optional = true, fetch = FetchType.LAZY)
@LazyToOne(value = LazyToOneOption.NO_PROXY)
@LazyToOne(LazyToOneOption.NO_PROXY)

I tried several variations of LazyToOne, but none of those worked. Is there another method I could use to only load this object when the getter is called?

Thanks,
Walter

Cameron McKenzie · **Posted:** Tue Jun 24, 2008 11:06 am

Here's a little tutorial on mapping one-to-one associations using JPA with Hibernate as the persistence framework.

http://jpa.ezhibernate.com/Javacode/learn.jsp?tutorial=17mappingonetooneassociations

I think what you want is a lazy attribute, as opposed to a full annotation:

Code:

@OneToOne(cascade=CascadeType.ALL, 
                         fetch=FetchType.LAZY)
@JoinColumn(name="detail_id")
public ExamDetail getDetail() {
  return detail;
}

The FetchType.LAZY will stop the eager loading of associated objects. With onetoone relationships, the default is eager.

Quote:

For performance reasons, it's always preferential to minimize the load placed on a system's memory. As such, most associations are set to a FetchType of LAZY. This is especially true for one to many and many to many relationships, where the impact of loading a large number of associated properties can be significant.

For one-to-many and many-to-many relationships, the default FetchType is LAZY. However, for one-to-one mappings, the default is EAGER, meaning that a class, and all of its one-to-one associations, are loaded into memory when it is invoked by the client. If this is not the behavior you want, you can set the FetchType to LAZY in your @OneToOne annotations.

http://www.thebookonhibernate.com/Javac ... sociations

nimo23 · **Posted:** Wed Mar 04, 2009 7:25 am

this

Code:

fetch=FetchType.LAZY

does not work for xToOne-Relationships.

The referenced one-to-one entity is always eager fetched, even FetchType.LAZY is set. So we have to use something like LazyToOne or
@Fetch(SELECT)!

nimo23 · **Posted:** Wed Mar 04, 2009 7:38 am

Even this does not work:

Code:

 @Fetch(FetchMode.SELECT)
@OneToOne(fetch = FetchType.LAZY, optional = true, targetEntity=EClass.class)
@JoinColumns({..
private EClass eclass;
//getter/setter

the entity Eclass is always eager fetched.

nimo23 · **Posted:** Wed Mar 04, 2009 7:48 am

Even this does not work, collection is ALWAYS eager fetched.

Code:

@LazyToOne(LazyToOneOption.PROXY)
@Fetch(FetchMode.SELECT)
@OneToOne(fetch = FetchType.LAZY, optional = true, targetEntity=Postage.class)
@JoinColumns({...

any Ideas, why the annotations does not work?

nimo23 · **Posted:** Wed Mar 04, 2009 7:49 am

Even this does not work, collection is ALWAYS eager fetched.

Code:

@LazyToOne(LazyToOneOption.PROXY)
@Fetch(FetchMode.SELECT)
@OneToOne(fetch = FetchType.LAZY, optional = true, targetEntity=EClass.class)
@JoinColumns({...

any Ideas, why the annotations does not work?

3e7 · **Joined:** Wed Mar 18, 2009 2:26 pm **Posts:** 1

nimo23 wrote:

Even this does not work, collection is ALWAYS eager fetched.

Code:

@LazyToOne(LazyToOneOption.PROXY)
@Fetch(FetchMode.SELECT)
@OneToOne(fetch = FetchType.LAZY, optional = true, targetEntity=EClass.class)
@JoinColumns({...

any Ideas, why the annotations does not work?

write @OneToOne(fetch = FetchType.LAZY, optional=false) and all be OK.

The feature of xxxToOne is the "optional=false" must be declared