When does Grails assign an ID to an object?

问题:

A Grails 2.3.4 application is connecting to an Oracle database using the following domain class:

class Person {

    String name

    static mapping = {
        id column: "PERSON_ID", generator: "sequence", params: [sequence: 'person_seq']
    }
}

The PersonController makes a call to a method in PersonService and it makes a call to UtilService. The method in UtilService being called has some logic based on wether this Person object is new:

if (personInstance.id == null) { ... }

What I have found is that the id property of personInstance (which is passed through the method calls described above) is assigned when the UtilService is called.

The controller action calling PersonService is @Transactional, and the services do not have any transaction configuration.

So, a couple of questions:

• When is id value assigned by GORM (I assumed at insert but that seems wrong)?
• Is there a better way of checking if the object is new (isAttached() returns true so that's not good for me)?

EDIT: save() has not been called on the personInstance when UtilService does the id check.

回答1:

The id is assigned when you call save(). For most persistence calls, Hibernate delays flushing the change until it feels it has to flush) to ensure correctness. But save() calls are treated differently. I believe the motivation is that even if we know that flush() will eventually be called, even if it's at the very end of the request, we want to retrieve the id early so it doesn't suddenly change.

Note that a service that does "not have any transaction configuration" is transactional - the only way to get a non-transactional service is to remove all @Transactional annotations (the newer Grails annotation and the older Spring annotation) and add

static transactional = false

All other services are transactional, although you can configure individual methods to be ignored ## Headin.

回答2:

Turns out, I had a findBy which was flushing the session:

utilService.someMethod(Person.findByUsername(username))

It was at this point that the id was populated.

Got around it by using withNewTransaction:

def personInstance = Person.withNewSession { Person.findByUsername(username) }
utilService.someMethod(personInstance)

Which now leads me onto the next question...