Should value object hold reference to entity?

问题

Should value object hold reference to entity in DDD methodology?

EDIT

@Dmitry:

This is probably my case. Here I attach class diagram where the Account hold references to collection of IInvoiceable items. I treat with Tenant as entity, but it owns only 1 account and i dont think that Account needs identity. its part of Tenant. Or should I treat it as Entity? To me it doesnt make sense.

回答1:

Yes it can. This would be a relatively obscure case but DDD allows for it and it can be useful. From the DDD book by Eric Evans:

VALUE OBJECTS can even reference ENTITIES. For example, if I ask an online map service for a scenic driving route from San Francisco to Los Angeles, it might derive a Route object linking L.A. and San Francisco via the Pacific Coast Highway. That Route object would be a VALUE, even though the three objects it references (two cities and a highway) are all ENTITIES.

page #98

回答2:

Take a look at this links, hope it will be helpful

http://lostechies.com/jimmybogard/2008/05/21/entities-value-objects-aggregates-and-roots/

http://domain-driven-design.3010926.n2.nabble.com/Entities-reference-another-Aggregate-or-point-to-another-Aggregate-td5840084.html

来源：https://stackoverflow.com/questions/9498637/should-value-object-hold-reference-to-entity