How can I determine if a domain class instance is persistent, i.e. was loaded from a database? I'm looking for a property/method that would return false for this object
def book = new Book(name: 'foo')
But would return true for this object
def book = Book.findByName('foo')
Is checking for a truthy id property reliable, e.g.
boolean isPersistent = book.id
Use the isAttached method or its attached property form:
def book = new Book(name: 'foo')
assert !book.attached
book.save(flush: true)
Book.withSession { it.clear() }
book = Book.findByName('foo')
assert book.attached
If you don't use assigned ids, checking that the instance has a non-null id will work but isn't always going to be correct since you can always assign a long value to the id property of a non-persistent instance (it will be updated when saved).
Note that using isAttached will fail for persistent instances that are detached from a Hibernate Session - it's only true if both persistent (i.e. it was instantiated from database data) and currently associated with a session.