In a presentation by Dennis Doomen on http://cqrs.wordpress.com/ there
is the following statement included:
"Aggregate Roots have no relationships (!)"
As I have not much experience with CQRS so far I wonder if this is
correct.
What do you think?
The statement is rather bold, and can easily be put away as untrue. However, I think what Dennis means, is that aggregates do not have direct relationships with each other. One aggregate should never force updates in another aggregate directly. Instead, that should be done through events and (here it is again) a saga. Aggregate roots may very well have relationships, even with other aggregates. But they should be of an indirect nature, meaning that only the identifier of the other aggregate should be stored. Direct relationships (as in java references to objects) should only exist between entities within the same aggregate.
In other words, I don’t think Dennis is wrong, but the statement requires some explanation.
Allard