Day 1: Documents, Collections, and CRUD | MongoDB in 5 Days

The Document Model

MongoDB stores data as BSON (Binary JSON) documents. A document is like a row in SQL — but it can have nested objects and arrays. No fixed schema required.

Install and connect

# Mac: brew install mongodb-community
# Linux: see mongodb.com/docs/manual/installation
# Or use MongoDB Atlas free tier (cloud)

# Start the shell
mongosh

mongosh CRUD

// Select database (creates if doesn't exist)
use myapp

// INSERT
db.users.insertOne({ name: 'Alice', age: 28, role: 'admin' })
db.users.insertMany([
  { name: 'Bob', age: 32 },
  { name: 'Carol', age: 25 }
])

// FIND
db.users.find()              // all documents
db.users.findOne({ name: 'Alice' })
db.users.find({ age: { $gte: 28 } })  // age >= 28

// UPDATE
db.users.updateOne(
  { name: 'Alice' },
  { $set: { role: 'superadmin' } }
)

// DELETE
db.users.deleteOne({ name: 'Carol' })
db.users.deleteMany({ age: { $lt: 18 } })

💡

Every document gets an _id field automatically. It's a 12-byte ObjectId that encodes a timestamp. You can use it to sort documents by creation time without storing a separate createdAt field: .sort({ _id: -1 }).

📝 Day 1 Exercise

Insert and Query Documents

Day 1 Summary

MongoDB stores BSON documents — like JSON with more types. Collections are like tables.
insertOne, insertMany, find, findOne, updateOne, deleteOne — the core operations.
Every document gets an auto-generated _id ObjectId.
No schema required. Documents in the same collection can have different fields.

Day 2: Queries and Operators

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