Stop 07 · NoSQL DatabasesTopics · 4/12

CRUD Operations

In short

Create, read, update, delete: the same four jobs as SQL, with MongoDB's own verbs. Learn the filter and update operators and you can write most API endpoints.

Create, Read, Update, Delete — the fundamental operations for working with MongoDB documents, using methods like `insertOne`, `find`, `updateOne`, `deleteOne`.

The blob pins, swaps and removes coloured cards on a hostel cork board.

Think of it like this

The hostel notice board

Pin a new notice (create). Scan for anything about the cricket match (read). Change the date on the fest notice (update). Pull down last month's water-cut warning (delete). MongoDB's CRUD methods are those four moves, done with filters instead of your eyes.

Watch it happen

Managing notices

API

MongoDB

insertOne({ title… })

1/6Create: add one notice. MongoDB gives it an _id.

The big ideas

What you need to know

insertOne and insertMany

Add documents. insertMany is much faster than looping insertOne for bulk data.

find with operators

Filters use operators like $gt, $in and $regex. { year: { $gt: 2 } } means year above 2.

Update operators

$set changes fields, $inc adds to numbers, $push appends to arrays. Use replaceOne only to swap a whole document.

deleteOne and deleteMany

Careful: an empty filter {} matches everything, so deleteMany({}) empties the collection.

See it in code

Walk through the code

1const notices = db.collection("notices");2 3await notices.insertOne({ title: "Fest on Friday", tag: "events", likes: 0, createdAt: new Date() });4 5const latest = await notices6  .find({ tag: { $in: ["sports", "events"] } })7  .sort({ createdAt: -1 })8  .limit(10)9  .toArray();10 11await notices.updateOne({ title: "Fest on Friday" }, { $set: { title: "Fest on Saturday" }, $inc: { likes: 1 } });12 13await notices.deleteMany({ expiresAt: { $lt: new Date() } });

1/4Create one notice. The driver adds an _id if you don't.

db here is client.db('college') from the official mongodb driver. Every method returns a promise.

Save yourself the pain

Common mistakes

Oops

Reading a document, changing it in JavaScript, then saving the whole thing back.

Do this instead

Two requests can overwrite each other. Use $set or $inc so MongoDB changes just those fields atomically.

Oops

Passing user input straight into a filter, like find(req.body).

Do this instead

A crafted body like { $ne: null } can match everything. Validate input and build filters yourself.

Your mission

Notice board API

~30 min

Quick check

Which update safely adds 1 to a likes counter when many users click at once?

Go deeper

1Practice each CRUD operation against a local MongoDB collection.
2Learn the query operators (`$gt`, `$in`, `$regex`) for more advanced `find` queries.
3Compare `updateOne` vs `updateMany` and when each applies.