hibernate - Optimistic locking not throwing exception when manually setting version field

Question

I have a Spring Boot 1.3.M1 web application using Spring Data JPA. For optimistic locking, I am doing the following:

1. Annotate the version column in the entity: @Version private long version;. I confirmed, by looking at the database table, that this field is incrementing properly.
2. When a user requests an entity for editing, sending the version field as well.
3. When the user presses submit after editing, receiving the version field as a hidden field or something.

4. Server side, fetching a fresh copy of the entity, and then updating the desired fields, along with the version field. Like this:

   User user = userRepository.findOne(id);
   user.setName(updatedUser.getName());
   user.setVersion(updatedUser.getVersion());
   userRepository.save(user);
   

I was expecting this to throw exception when the versions wouldn't match. But it doesn't. Googling, I found some posts saying that we can't set the @Vesion property of an attached entity, like I'm doing in the third statement above.

So, I am guessing that I'll have to manually check for the version mismatch and throw the exception myself. Would that be the correct way, or I am missing something?

Answer 1

Unfortunately, (at least for Hibernate) changing the @Version field manually is not going to make it another "version". i.e. Optimistic concurrency checking is done against the version value retrieved when entity is read, not the version field of entity when it is updated.

e.g.

This will work

Foo foo = fooRepo.findOne(id);  // assume version is 2 here
foo.setSomeField(....);

// Assume at this point of time someone else change the record in DB, 
// and incrementing version in DB to 3

fooRepo.flush();  // forcing an update, then Optimistic Concurrency exception will be thrown

However this will not work

Foo foo = fooRepo.findOne(id);  // assume version is 2 here
foo.setSomeField(....);
foo.setVersion(1);
fooRepo.flush();  // forcing an update, no optimistic concurrency exception
                  // Coz Hibernate is "smart" enough to use the original 2 for comparison

There are some way to workaround this. The most straight-forward way is probably by implementing optimistic concurrency check by yourself. I used to have a util to do the "DTO to Model" data population and I have put that version checking logic there. Another way is to put the logic in setVersion() which, instead of really setting the version, it do the version checking:

class User {
    private int version = 0;
    //.....

    public void setVersion(int version) {
        if (this.version != version) {
            throw new YourOwnOptimisticConcurrencyException();
        }
    }

    //.....
}