Hibernate Performance Tips: Dirty Collection Effect | Java Code Geeks

Why using property mapping Hibernate runs queries during commit and using field mapping are not executed? When a Transaction is committed, Hibernate execute a flush to synchronize the underlying persistent store with persistable state held in memory. When property mapping is used, Hibernate calls getter/setter methods to synchronize data, and in case of getOfficers method, it returns a dirty collection (because of unmodifiableList call). On the other side when we are using field mapping, Hibernate gets directly the field, so collection is not considered dirty and no re-creation is required.
But we have not finished yet, I suppose you are wondering why we have not removed Collections.unmodifiableList from getter, returning Hibernate collection? Yes I agree with you that we finished quickly, and change would look like @OneToMany(cascade={CascadeType.ALL}) public List<Officer> getOfficers() {officers;} but returning original collection ends up with an encapsulation problem, in fact we are broken encapsulation!. We could add to mutable list anything we like; we could apply uncontrolled changes to the internal state of an object.
Using an unmodifiableList is an approach to use to avoid breaking encapsulation, but of course we could have used different accessors for public access and hibernate access, and not calling Collections.unmodifiableList method.
Considering what we have seen today, I suggest you to use always field annotations instead of property mapping, we are going to save from a plenty of surprises.
Hope you have found this post useful.
via Hibernate Performance Tips: Dirty Collection Effect | Java Code Geeks.