CODEWITHSUNDEEP
domain-driven-designcqrs
andrey.ladniy
andrey.ladniy

Reputation: 1674

Сompleteness of data in the event when DDD CQRS used

What data should be contained in the event? Only data that is specific to this event or some data from boundary context too.

For example. I have account with domain and name properties

account(id, name, domain)

When I change account name NameChanged(id, name) event is created. But when this event is used for read side projection (cassandra db) I need to fill two tables (example does not use a materialized view):

accounts(id, name, domain) (primary key only `id`)
accountsByDomain(domain, id, name) (primary key contains `domain` and `id`)

Second table can not be synced by name, because where is no domain in the event.

Question: must be the event as simple as possible (and calls the state of the entity to get information that might have been different at the time the event occurred) or must it have complete information for read side projection

Upvotes: 0

Views: 71

Answers (1)

VoiceOfUnreason
VoiceOfUnreason

Reputation: 57239

We aren't usually limited to processing an event in isolation - the identifiers in the event are available to allow us to look up the other information we need (which could, for example, be included in other events in the same stream).

Reviewing Greg Young's talk on Polyglot Data may help clarify this idea.

Upvotes: 1

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