Creating Event Handlers

Handlers react to database events automatically.

Location:

/src/resources/{name}/handlers/{handlerName}.js

Template

import db from 'db';

const myService = db.services.myResource;

myService.on('created', async ({ doc }) => {
  // Handle creation
});

myService.on('updated', async ({ doc, prevDoc }) => {
  // Handle update
});

myService.on('removed', async ({ doc }) => {
  // Handle removal
});

Events

created

{ doc }

service.create()

updated

{ doc, prevDoc }

service.updateOne/Many()

removed

{ doc }

service.remove()

Common Patterns

Create related record:

taskService.on('created', async ({ doc }) => {
  await eventService.create({
    type: 'task.created',
    data: { task: doc },
    project: doc.project,
  });
});

Update parent on child change:

docService.on('created', async ({ doc }) => {
  if (doc.role === 'case-study') {
    await projectService.updateOne(
      { _id: doc.project._id },
      (p) => ({ ...p, caseStudy: doc })
    );
  }
});

React to specific field change:

import ifUpdated from 'helpers/db/ifUpdated';

taskService.on('updated', ifUpdated(['status'], async ({ doc, prevDoc }) => {
  // Only runs when status changed
}));

Cleanup on delete:

docService.on('removed', async ({ doc }) => {
  await eventService.remove({ 'data.doc._id': doc._id });
});

Rules

• Keep handlers fast (don't block response)
• Use

  atomic.update

  for silent bulk updates (no events)
• Use

  ifUpdated

  helper to filter field changes