Ok I’ve changed my mind. I have been trying to deal with VOs a bunch lately and after watching this http://www.infoq.com/presentations/Value-Objects-Dan-Bergh-Johnsson it clarified a couple of things for me. Commands and Event are messages (and not objects, objects are data + behavior), in some respects much like DTOs, they communicate data about an event and … Read more
Under the surface, the two approaches are equivalent. However, you get most of the standard OO benefits when using a class: encapsulation, inheritance, etc. Also, look at the following examples: $arr[‘naem’] = ‘John’; is perfectly valid and could be a difficult bug to find. On the other hand, $class->setNaem(‘John’); will never work.
Ignore all the crazy answers about thread safe etc, that has nothing to do with DDD. (I’ve yet to see a thread safe O/R mapper or other DDD friendly dal) Imagine a value object for weights. lets say we have a KG value object. sample (edited for clarity): var kg75 = new Weight(75); joe.Weight = … Read more
It depends entirely on how you’re going to use the object. Public fields aren’t inherently evil, it’s just bad to default everything to being public. For example the java.awt.Point class makes its x and y fields public, and they aren’t even final. Your example seems like a fine use of public fields, but then again … Read more
It’s ok to store Value Objects in a separate table, for the very reasons you’ve described. However, I think you’re misunderstanding Entities vs VOs – it’s not a persistence related concern. Here’s an example: Assume that a Company and Person both have the same mail Address. Which of these statements do consider valid? “If I … Read more
Reduced to the essential distinction, identity matters for entities, but does not matter for value objects. For example, someone’s Name is a value object. A Customer entity might be composed of a customer Name (value object), List<Order> OrderHistory (List of entities), and perhaps a default Address (typically a value object). The Customer Entity would have … Read more