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Counters are everywhere — likes, view counts, inventory, rate-limit buckets. The naïve implementation is read, add one, save — and it’s wrong the moment two requests land at the same time. This recipe shows the right way: use Esix’s increment and decrement, which translate to MongoDB’s $inc operator and run atomically on the server. Esix features used: increment, decrement on QueryBuilder.

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What You’ll Build

POST   /posts/:id/view → record a view (anyone can call)
POST   /posts/:id/like → like a post (authenticated)
DELETE /posts/:id/like → undo a like
Each endpoint runs in a single round trip and is safe under arbitrary concurrency.

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The Post Model

Two counters on the document — no userId lists, no per-action collection. If you also need to know who liked a post, model that with a separate Like collection alongside; for the count itself, a number is enough. 
// src/models/post.ts
import { BaseModel } from 'esix'

export default class Post extends BaseModel {
  public title = ''
  public body = ''
  public viewCount = 0
  public likeCount = 0
}

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Why Not Read-Modify-Write?

This pattern looks fine and is wrong: 
// ❌ Don't do this.
const post = await Post.find(id)
post.viewCount += 1
await post.save()
If two requests run this at the same time, both read the same viewCount, both write viewCount + 1, and one of the increments vanishes. The fix is to push the increment all the way down to MongoDB: 
// ✅ Atomic — translates to $inc.
await Post.where('id', id).increment('viewCount')
increment returns the number of documents modified (0 when nothing matched), which is enough for the route handler to tell “found and updated” from “not found”.

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View Counter

A view endpoint is the simplest case — single field, single increment: 
// src/routes/posts/views.ts
import { Router } from 'express'
import Post from '../../models/post'

const router = Router({ mergeParams: true })

router.post('/view', async (request, response) => {
  const modified = await Post.where('id', request.params.id).increment(
    'viewCount'
  )

  if (modified === 0) {
    return response.status(404).json({ error: 'Post not found' })
  }

  response.status(204).end()
})

export default router

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Like and Unlike

Likes are symmetric: one route increments, the mirror route decrements. The optional second argument lets you bump by something other than 1: 
// src/routes/posts/likes.ts
import { Router } from 'express'
import Post from '../../models/post'
import { requireAuth } from '../../auth/require-auth'

const router = Router({ mergeParams: true })

router.post('/like', requireAuth, async (request, response) => {
  const modified = await Post.where('id', request.params.id).increment(
    'likeCount'
  )

  if (modified === 0) {
    return response.status(404).json({ error: 'Post not found' })
  }

  response.status(204).end()
})

router.delete('/like', requireAuth, async (request, response) => {
  const modified = await Post.where('id', request.params.id).decrement(
    'likeCount'
  )

  if (modified === 0) {
    return response.status(404).json({ error: 'Post not found' })
  }

  response.status(204).end()
})

export default router
Note: decrement accepts any positive number — decrement('likeCount', 5) would subtract five — and it doesn’t clamp at zero. If you need a floor, guard the call site or use a MongoDB conditional update.

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Bumping by More Than One

Both helpers take an optional second argument. Some everyday examples: 
// Award 10 points for finishing a challenge.
await User.where('id', userId).increment('score', 10)

// Charge a one-off fee against an account balance.
await Account.where('id', accountId).decrement('balance', 25)

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Bulk Increments

increment runs against the whole where clause, so you can bump many documents at once. This is great for batch reconciliation: 
// Mark every active subscription as having been billed once more.
const updated = await Subscription
  .where('status', 'active')
  .increment('billingCycles')
updated is the count of documents $inc actually touched — useful when you want to log “processed N records” or feed a progress UI.

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Pattern Notes

  • Counters belong on the parent. Don’t store viewCount in a sidecar collection — that just turns a one-document write into a join.
  • One increment per request. Avoid calling increment inside a loop; if you need to bump by N, pass N as the second argument.
  • Distinguish “missing” from “no-op”. increment returns 0 for both an empty where and a non-existent id — your route should return 404 in either case.

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What’s Next