Java – Hibernate Annotations – Which is better, field or property access


This question is somewhat related to Hibernate Annotation Placement Question.

But I want to know which is better? Access via properties or access via fields?
What are the advantages and disadvantages of each?

Best Solution

There are arguments for both, but most of them stem from certain user requirements "what if you need to add logic for", or "xxxx breaks encapsulation". However, nobody has really commented on the theory, and given a properly reasoned argument.

What is Hibernate/JPA actually doing when it persists an object - well, it is persisting the STATE of the object. That means storing it in a way that it can be easily reproduced.

What is encapsulation? Encapsulations means encapsulating the data (or state) with an interface that the application/client can use to access the data safely - keeping it consistent and valid.

Think of this like MS Word. MS Word maintains a model of the document in memory - the documents STATE. It presents an interface that the user can use to modify the document - a set of buttons, tools, keyboard commands etc. However, when you choose to persist (Save) that document, it saves the internal state, not the set of keypresses and mouse clicks used to generate it.

Saving the internal state of the object DOES NOT break encapsulation - otherwise you don't really understand what encapsulation means, and why it exists. It is just like object serialisation really.

For this reason, IN MOST CASES, it is appropriate to persist the FIELDS and not the ACCESSORS. This means that an object can be accurately recreated from the database exactly the way it was stored. It should not need any validation, because this was done on the original when it was created, and before it was stored in the database (unless, God forbid, you are storing invalid data in the DB!!!!). Likewise, there should be no need to calculate values, as they were already calculated before the object was stored. The object should look just the way it did before it was saved. In fact, by adding additional stuff into the getters/setters you are actually increasing the risk that you will recreate something that is not an exact copy of the original.

Of course, this functionality was added for a reason. There may be some valid use cases for persisting the accessors, however, they will typically be rare. An example may be that you want to avoid persisting a calculated value, though you may want to ask the question why you don't calculate it on demand in the value's getter, or lazily initialise it in the getter. Personally I cannot think of any good use case, and none of the answers here really give a "Software Engineering" answer.