[FIXED] How to use EntityManager to find an entity by id without hitting cache in one query?

Issue

I have a critical section of code where I need to read and lock an entity by id with pessimistic lock.

This section of code looks like this right now:

MyEntity entity = entityManager.find(MyEntity.class, key);
entityManager.refresh(entity, LockModeType.PESSIMISTIC_WRITE);

It works OK, but as I understand in case when there is no entity in the hibernate's cache, we will use 2 read transactions to a database. 1st transaction to find the entity by id and another transaction to refresh and lock the entity. Is it possible to use only one transaction in such scenario?

I would imagine something like:

boolean skipCache = true;
MyEntity entity = entityManager.find(MyEntity.class, key, 
    LockModeType.PESSIMISTIC_WRITE, skipCache);

But there is no such parameter like skipCache. Is there another approach to read an entity by id directly from the database by using EntityManager?

UPDATE:

This query will hit the first level cache in case the entity exists in the cache. Thus, it may potentially return the outdated data and that is why isn't suitable for critical sections where any read should be blocked:

MyEntity entity = entityManager.find(MyEntity.class, key, LockModeType.PESSIMISTIC_WRITE);

The question is about skipping the cache and not about locking.

Solution

I've just found a method getReference in the EntityManager which gets an instance, whose state may be lazily fetched. As said in the documentation:

Get an instance, whose state may be lazily fetched. If the requested instance does not exist in the database, the EntityNotFoundException is thrown when the instance state is first accessed. (The persistence provider runtime is permitted to throw the EntityNotFoundException when getReference is called.) The application should not expect that the instance state will be available upon detachment, unless it was accessed by the application while the entity manager was open.

As a possible solution to find and lock an up to date entity by id in one query we can use the next code:

MyEntity entity = entityManager.getReference(MyEntity.class, key);
entityManager.refresh(entity, LockModeType.PESSIMISTIC_WRITE);

This query will create an entity (no database query) and then refresh and lock the entity.

Answered By - Oleksandr
Answer Checked By - David Goodson (JavaFixing Volunteer)