Difference between CrudRepository findOne() and JpaRepository getOne()

Question

I read that getOne() is lazy loaded and findOne() fetches the whole entity right away. I\'ve checked the debugging log and I even enabled monitorin

Answer 1

It is just a guess but in 'pure JPA' there is a method of EntityManager called getReference. And it is designed to retrieve entity with only ID in it. Its use was mostly for indicating reference existed without the need to retrieve whole entity. Maybe the code will tell more:

// em is EntityManager
Department dept = em.getReference(Department.class, 30);  // Gets only     entity with ID property, rest is null
Employee emp = new Employee();
emp.setId(53);
emp.setName("Peter");
emp.setDepartment(dept);
dept.getEmployees().add(emp);
em.persist(emp);

I assume then getOne serves the same purpose. Why the queries generated are the same you ask? Well, AFAIR in JPA bible - Pro JPA2 by Mike Keith and Merrick Schincariol - almost every paragraph contains something like 'the behaviour depends on the vendor'.

EDIT:

I've set my own setup. Finally I came to conclusion that if You in any way interfere with entity fetched with getOne (even go for entity.getId()) it causes SQL to be executed. Although if You are using it only to create proxy (eg. for relationship indicator like shown in a code above), nothing happens and there is no additional SQL executed. So I assume in your service class You do something with this entity (use getter, log something) and that is why the output of these two methods looks the same.

ChlebikGitHub with example code
SO helpful question #1
SO helpful question #2

Answer 2

If data is not found the table for particular ID, findOne will return null, whereas getOne will throw javax.persistence.EntityNotFoundException. Both have their own pros and cons. Please see example below:

1. If data not found is not failure case for you (eg. You are just verifying if data the data is deleted and success will be data to be null), you can use findOne.
2. In another case, you can use getOne.

This can be updated as per your requirements, if you know outcomes.

Answer 3

Suppose you want to remove an Entity by id. In SQL you can execute a query like this :

"delete form TABLE_NAME where id = ?". 

And in Hibernate, first you have to get a managed instance of your Entity and then pass it to EntityManager.remove method.

Entity a = em.find(Entity.class, id);
em.remove(a);

But this way, You have to fetch the Entity you want to delete from database before deletion. Is that really necessary ?

The method EntityManager.getReference returns a Hibernate proxy without querying the database and setting the properties of your entity. Unless you try to get properties of the returned proxy yourself.

Method JpaRepository.getOne uses EntityManager.getReference method instead of EntityManager.find method. so whenever you need a managed object but you don't really need to query database for that, it's better to use JpaRepostory.getOne method to eliminate the unnecessary query.