Actions Events

Actions + events

Business logic lives in actions; cross-cutting effects run through events. Controllers stay thin (policy → validate → action → response). Actions take a plain input, never HttpContext. When an action needs a side effect (mail, notification, transmit, external HTTP), it emits a domain event; a listener in the module's start/events.ts receives it and runs the effect. This keeps actions synchronous domain code, keeps side effects composable (a new listener is a new file, not an edit to the action), and makes testing effortless — fake the emitter, fake the mail.

Rules

• Location: app/<mod>/actions/<verb_noun>.ts — one file per action.

• Shape: default-export a class with a single public method async handle(input): Promise<Result | void>. input is a plain interface. No HttpContext.

• Return or throw: return the primary value (a model, an id, void). Throw domain exceptions from app/<mod>/exceptions/ for expected failure paths (rate limits, permission denials, invariant violations).

• Side effects go through events. Anything that reaches out is emitted, not called inline:

  emitter.emit('user:registered', { user, token })
  

  This applies to every kind of effect without exception:

  Kind	Example call the action must not make
  Mail	mail.send(new WelcomeEmail(...))
  In-app notification	facteur.notification(...).send()
  SSE / realtime broadcast	transmit.broadcast(channel, payload)
  External HTTP	fetch('https://api.stripe.com/...')
  Audit log write	any write to an audits / activity_logs table that's cross-cutting

• Listeners live in app/<mod>/start/events.ts. Register with emitter.on('event:name', async (data) => { ... }). Preload the file from adonisrc.ts so it wires at boot (see [[module-scaffolding]]).

• Guards as helper functions at the top of the action file — e.g. requireManageRoles(executor) throws if not permitted. Keeps the action body short and the guard reusable across actions.

• Controllers call actions: await new Action().handle(input). Never instantiate an action inside another action; if two actions need shared work, extract a service (behavior with side effects) or a query (read-only).

Repo refs

• Action shape (.handle, no HttpContext): app/users/actions/create_user.ts.
• Reusable defense-in-depth guards: app/users/actions/sync_user_roles.ts.
• Event typing (declaration merge): app/users/types/events.ts; listener wiring: app/users/start/events.ts.

Doc refs

• AdonisJS emitter — https://docs.adonisjs.com/guides/digging-deeper/emitter

Workflow

Create a new action

1. Create app/<mod>/actions/<verb_noun>.ts (e.g. create_invoice.ts).
2. Declare an interface for the input — everything the action needs, as plain values. Pass auth / session only if the action must call auth.use(...).login(user).
3. Default-export a class:

   export default class CreateInvoice {
     async handle(input: CreateInvoiceInput): Promise<Invoice> {
       // guards, domain logic, DB writes
       // emit if there are side effects
       return invoice
     }
   }
   

4. Throw domain exceptions from app/<mod>/exceptions/ for expected failure paths.

Emit a domain event

Inside the action, at the point the side effect should trigger:

emitter.emit('<mod>:<event>', payload)

Naming: <mod>:<past-tense-verb> — user:registered, invoice:issued, role:changed.

Payload: plain, serializable. Include the primary entity + whatever the listener needs. Never reach for HttpContext fields.

Add a listener

1. Open (or create) app/<mod>/start/events.ts.
2. Add emitter.on('<event>', async (data) => { ... }).
3. Ensure () => import('#<mod>/start/events') is in adonisrc.ts preloads.
4. Multiple listeners on the same event are fine — one per side effect (one mail, one notification, one webhook).

Concurrency — actions that read-then-write a sequence

When the action derives a value from the current state of a set (next position in a list, next number in a sequence, unique slug), two concurrent invocations against the same parent will both read the same max and produce a duplicate. Two-layer defense:

1. unique(...) on the schema so the DB rejects the second write. A safety net, not a UX.
2. db.transaction() with SELECT parent FOR UPDATE to serialize the compute-and-insert on the parent aggregate. Lock the parent, not the aggregated table.

async handle(input: AddItemInput): Promise<Item> {
  const item = await db.transaction(async (trx) => {
    // Lock the parent row for the length of the trx.
    await Parent.query({ client: trx })
      .where('id', input.parentId)
      .forUpdate()
      .firstOrFail()

    const last = await Item.query({ client: trx })
      .where('parent_id', input.parentId)
      .max('position as max')
      .first()

    const position = (Number((last as any)?.$extras?.max) || 0) + 1

    return Item.create(
      { parentId: input.parentId, position, ...input.payload },
      { client: trx }
    )
  })

  await emitter.emit('item:added', { item, parentId: input.parentId })
  return item
}

Same shape for deletes with reordering: hold the parent lock, delete, decrement the range.

Do heavy I/O (file upload, external HTTP) outside the transaction so the lock isn't held while bytes stream.

Testing

• Unit-test the action with sinon stubs — see [[testing]].
• Fake the emitter in endpoint tests to verify emission without running listeners: emitter.fake(['user:registered']) then fake.assertEmitted('user:registered').
• End-to-end listener test: await emitter.emit('user:registered', payload) and assert the side effect (mail sent, notification row created, etc).

Anti-patterns

• ❌ Action takes HttpContext — extract the pieces it needs and pass those as plain fields.
• ❌ Action calls mail.send(...) / facteur.notification(...).send() / transmit.broadcast(...) directly — emit an event, let the listener do it.
• ❌ Read-then-write on a computed column (next position, next sequence number) without .forUpdate() on the parent + unique(...) on the schema — the race produces duplicates.
• ❌ Business logic in the controller (if (user.isX) { ... } await something()) — move it to an action.
• ❌ Multiple public methods on an action — split into separate action files.
• ❌ Listener that reaches into another module's DB directly — cross-module effects should emit their own domain event from the source module and be handled by a listener that owns the destination.
• ❌ Emitting from inside a db.transaction(...) — if the transaction rolls back, the listeners already ran. Emit after the trx commits.

Related skills

[[module-scaffolding]] · [[routes]] · [[crud]] · [[testing]] · [[mail]] · [[notifications]]