Messages

All messages flowing thru the system are loosely typed objects with a minimal set of required fields:

• type: string - command or event type. for commands it's recommended to name it as a call to action (i.e. "createUser"), while for events it should describe what happened in a past tense (i.e. "userCreated").
• payload: any - command or event data
• context: object - key-value object with information on context (i.e. logged in user ID). context must be specified when a command is being triggered by a user action and then it's being copied to events, sagas and subsequent commands

Other fields are used for message routing and their usage depends on the flow:

• aggregateId: string|number|undefined - unique aggregate identifier
• aggregateVersion: number
• sagaId: string|number|undefined
• sagaVersion: number

Commands

• sent to CommandBus manually
• being handled by Aggregates
• may be enqueued by Sagas

Command example:

{
  "type": "signupUser",
  "aggregateId": null,
  "payload": {
    "profile": {
      "name": "John Doe",
      "email": "[email protected]"
    }, 
    "password": "test"
  },
  "context": {
    "ip": "127.0.0.1",
    "ts": 1503509747154
  }
}

Events

• produced by Aggregates
• persisted to EventStore
• may be handled by Projections, Sagas and Event Receptors

Event example:

{
  "type": "userSignedUp",
  "aggregateId": 1,
  "aggregateVersion": 0,
  "payload": {
    "profile": {
      "name": "John Doe",
      "email": "[email protected]"
    }, 
    "passwordHash": "098f6bcd4621d373cade4e832627b4f6"
  },
  "context": {
    "ip": "127.0.0.1",
    "ts": 1503509747154
  }
}