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    <p>Ok I've changed my mind. I have been trying to deal with VOs a bunch lately and after watching this <a href="http://www.infoq.com/presentations/Value-Objects-Dan-Bergh-Johnsson">http://www.infoq.com/presentations/Value-Objects-Dan-Bergh-Johnsson</a> it clarified a couple of things for me.</p> <p>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 they themselves encapsulate no behavior.</p> <p>Value Objects are not like DTOs at all. They are a domain representation and they are, generally speaking, rich on behavior like all other domain representations.</p> <p>Commands and Events communicate information into and out of the domain respectively, but they themselves do not encapsulate any behavior. From that perspective it seems wrong and a possibly a violation context boundaries to pass VOs inside of them. </p> <p>To paraphrase Oren (though he was referring to nHibernate and WCF) "Don't send your domain across the wire". <a href="http://ayende.com/Blog/archive/2009/05/14/the-stripper-pattern.aspx">http://ayende.com/Blog/archive/2009/05/14/the-stripper-pattern.aspx</a></p> <p>If you want to communicate a value object, then I suggest passing the necessary attributes needed to re-construct the VO within them instead.</p> <p>Original Text (for posterity):</p> <p>If you are asking if Value Objects can be passed by the domain model to events or passed in by commands, I don't really see a huge problem with the former, though the latter may violate some of the rules of the aggregate root being the "owner" of values.</p> <p>That said a value object represents concepts like for example a color. You don't <em>have</em> green, you <em>are</em> green or not. There seems to be nothing intrinsically wrong with a command telling you that you are green by passing this.</p> <p>Reading the chapter from DDD on the Aggregate Root pattern explains Entities and Value Objects quite well and is worth reading over a few times.</p>
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    1. POValue Objects in CQRS - where to use
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    1. USChris Nicola
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    1. COI think it's ok from pure DDD-perspective to have shared VO's, but from cqrs point of view, this can introduce some technical problems, like versioning of events if Event Sourcing is applied. And then the natural question arises, is this really just a technical issue, or is it something intrinsically wrong with the whole idea.
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    2. COThe understanding I took from the DDD book is that while aggregate roots are the owners of their respective entities and value objects they may pass on a reference to those objects transiently. The sole purpose of the aggregate root is to define the transactional boundaries of the system. Again, I may be misinterpreting some of this and as always YMMV. While it would definitely be bad to serialize an entity as part of an event I can't see any problems for VOs since they should represent a true immutable value.
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    3. CO"Value Objects are not like DTOs at all. They are a domain representation and they are [...] rich on behavior like all other domain representations." I'd strongly disagree with the latter part. While they are part of the domain (eg. defining what an *Address* is), they're meant to be disposable and not have any behaviour attached to them. That's why they're usually immutable, to prevent you from wanting to mess with your VO.
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