cqrs-pattern

CQRS: Separating Command Validation from Read Model Updates

In a traditional CRUD system, reads and writes share the same model, which causes contention at scale. This workflow implements CQRS by validating a command against the aggregate, persisting the resulting event, and updating the read model as a separate projection. The read model can be queried independently.

Workflow

command, aggregateId, data
           |
           v
+--------------------------+     +----------------------+     +---------------------------+
| cqrs_validate_command    | --> | cqrs_persist_event   | --> | cqrs_update_read_model    |
+--------------------------+     +----------------------+     +---------------------------+
  valid: true                     eventId generated            projection updated for
  event: {type:                   version: 5                   aggregateId
  "ITEM_UPDATED", data}          persisted: true

Workers

ValidateCommandWorker -- Validates command for aggregateId. Returns valid: true and an event with type: "ITEM_UPDATED" and the command data.

PersistEventWorker -- Stores the event. Returns a generated eventId, version: 5, persisted: true.

UpdateReadModelWorker -- Updates the read model projection for the aggregate. Returns updated: true.

QueryReadModelWorker -- (Available for queries) Returns the current state: {id: aggregateId, name: "Widget"}.

Tests

8 unit tests cover command validation, event persistence, read model updates, and queries.

Running

See ../../RUNNING.md for setup and execution instructions.