Mongoose Hooks to Emit Events

emitter.js

const events = require("events")
module.exports = new events.EventEmitter();

model.js

const mongoose = require("mongoose")
const emitter = require("./emitter")

const wineSchema = new mongoose.Schema({
  name: String,
  price: Number
})

wineSchema.post("save", (wine) => {
  emitter.emit("wineCreated", wine)
})

module.exports = mongoose.model("Wine", wineSchema)

server.js

const express = require("express"),
      mongoose = require("mongoose");

const Wine = require("./model"),
      emitter = require("./emitter");

const app = express()

const dbUri = process.env.MONGODB_URI || "mongodb://localhost/dev";

const dbOptions = {
  useCreateIndex: true,
  useNewUrlParser: true,
  useUnifiedTopology: true,
  useFindAndModify: false
}

mongoose.connect(dbUri, dbOptions)
  .then(console.log("Connected to DB."))
  .catch(console.error)

emitter.on("wineCreated", (wine) => {
  console.log("Created:", wine)
})

app.listen(8080)

app.get("/", async (req, res) => {
  await new Wine({ name: "My Wine", price: 20 }).save()
  res.sendStatus(200)
})

Making a GET request to localhost:8080/ will cause a Wine record to be inserted, which will cause the "wineCreated" event to be fired. This can be used to have database operations drive events, allowing for a cleaner separation of concerns (versus a middleware which interfaces with the DB and acts as a logic layer).