Java – Hibernate one-to-one: getId() without fetching entire object

hibernatejavajpa

I want to fetch the id of a one-to-one relationship without loading the entire object. I thought I could do this using lazy loading as follows:

class Foo { 
    @OneToOne(fetch = FetchType.LAZY, optional = false)
    private Bar bar; 
}


Foo f = session.get(Foo.class, fooId);  // Hibernate fetches Foo 

f.getBar();  // Hibernate fetches full Bar object

f.getBar().getId();  // No further fetch, returns id

I want f.getBar() to not trigger another fetch. I want hibernate to give me a proxy object that allows me to call .getId() without actually fetching the Bar object.

What am I doing wrong?

Best Answer

Use property access strategy

Instead of

@OneToOne(fetch=FetchType.LAZY, optional=false)
private Bar bar;

Use

private Bar bar;

@OneToOne(fetch=FetchType.LAZY, optional=false)
public Bar getBar() {
    return this.bar;
}

Now it works fine!

A proxy is initialized if you call any method that is not the identifier getter method. But it just works when using property access strategy. Keep it in mind.

See: Hibernate 5.2 user guide

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