Zod for event validation

[vsnig]

Hey,

Just wanted to bring attention to a great tool that can greatly increase our confidence while processing events.

For those who don't know, Zod lets us create a schema and then validate an object against that schema (plus inferring Typescript type as a bonus)

So for example in BFF template when we materialize upstream thing, in models/thing.js we could do:

import { z } from 'zod'

const thingEventSchema = z.object({
  type: z.enum(['thing-submitted', 'thing-resubmitted', 'thing-rejected', 'thing-approved']),
  thing: z.object({
    id: z.string(),
    name: z.string(),
    status: z.enum(['SUBMITTED', 'RESUBMITTED', 'REJECTED', 'APPROVED']).optional()
  }),
  timestamp: z.number(),
})

export const toUpdateRequest = (uow) => {
  const event = thingEventSchema.parse(uow.event) // will throw if the event doesn't satisfy the schema

  // Now we can be sure that we're working with the thing we are expecting to work with so we can proceed with confidence
  // plus, `event` is now typed, and even if we don't use Typescript, we get Intellisense suggestions for properties of `event`

  return {
    Key: {
      pk: event.thing.id,
      sk: DISCRIMINATOR,
    },
    ...updateExpression({
      ...event.thing,
      status: EVENT_STATUS_MAP[event.type] || event.thing.status,
      ...

This also forces us to write tests that resemble real events

We can also validate outgoing events, for example in high responsibility services like ESG.

To summarize, a great tool that can help us in distributed event driven architecture.