Software Architect's Handbook

Using event-sourcing with CQRS

Although CQRS can be used without events, they do complement each other so it is common for systems that use CQRS to leverage the use of events. Events are one way to effectively communicate state changes so that the query model can stay up to date as the command model updates data.

As we saw in the Event-sourcing section earlier in this chapter, event-sourcing involves persisting events that take place in a system such that the event store can serve as the record of truth. When the command model alters the state of the system, events can be raised so that the query model can be kept in sync.

Keeping the query and command models in sync is necessary when the query and command models use separate data stores. ...