Why should you care?

One inbox query returns every notification type. Separate collections would force unions in the app for a single feed.

See it live — copy this example

Open mongosh or MongoDB Compass, select database nosqlverse, then run the example. Change one field and run again.

db.events.insertMany([
  { type: "page_view", userId: 1, path: "/courses", at: new Date() },
  { type: "purchase", userId: 1, orderId: ObjectId(), amount: 999, at: new Date() },
  { type: "login", userId: 2, ip: "1.2.3.4", at: new Date() }
])
db.events.find({ type: "purchase", amount: { $gte: 500 } })
db.events.createIndex({ type: 1, at: -1 })

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• All events share type and at, but other fields differ.
• Queries usually filter type first.
• A compound index on type + at supports timelines per event kind.

Practice next

1. Insert the three event shapes.
2. Query only logins for user 2.
3. Add a validator that requires type and at.
4. Add type: "quiz_score" with score field.
5. Project differently per type in the app layer.

Remember

One collection can hold multiple shapes. Use a discriminator field like type. Index type plus time for feeds.

Activity feed for SaaS

A project tool stores comments, uploads, and status changes in activities with type.

Outcome: One timeline API serves the whole project activity stream.