Should Command / Handles hold the full aggregates or only its id?

Question

I'm trying to play around with DDD and CQRS.

And I got this two solutions :

• add AggregateId to my command / event. It's nice beauce I can use my command as my web service's parameter, and I can as well return some instance of my command to my forms for saying "you can do this command,t his one and this one"

• add my full Aggregate to my command / event. It's nice because I'm sure that I won't load my aggregate 100 times if there is a lot of event going on, I'll just pass my reference around (for instance I won't load it in my command's validator and in my command handler). But i'd add to create a parameter class for each command wih only the id.

For now I have the id in the commands and the full model in the events (I trust my unit of work for caching the Load(aggregateId) so i won't execute the same request 100 for 1 command).

Is there a right / better way ?

Answer 1

Yes your current approach is correct - reference the aggregate with an identity value on the command. A command is meant to be serialized and sent across process boundaries. Also, a command is normally constructed by a client who may not have enough information to create an entire aggregate instance. This is also why an identity should be used. And yes, your unit of work should take care of caching an aggregate for the duration of a unit of work, if need be.