MongoDB Fundamentals in Practice — CRUD, Indexes, and Aggregation Pipelines

# GPG
curl -fsSL https://www.mongodb.org/static/pgp/server-7.0.asc | \
  sudo gpg -o /usr/share/keyrings/mongodb-server-7.0.gpg --dearmor

echo "deb [ arch=amd64,arm64 signed-by=/usr/share/keyrings/mongodb-server-7.0.gpg ] \
  https://repo.mongodb.org/apt/ubuntu jammy/mongodb-org/7.0 multiverse" | \
  sudo tee /etc/apt/sources.list.d/mongodb-org-7.0.list

sudo apt update && sudo apt install -y mongodb-org
sudo systemctl enable --now mongod

# mongosh
mongosh

// DB
use mydb

// list
show collections

// ( when )
db.createCollection("users")

// ── Create ──────────────────────────────────────
db.users.insertOne({
  name: "Alice",
  email: "alice@example.com",
  age: 30,
  tags: ["admin", "active"],
  createdAt: new Date()
})

db.users.insertMany([
  { name: "Bob", email: "bob@example.com", age: 25 },
  { name: "Carol", email: "carol@example.com", age: 35 }
])

// ── Read ────────────────────────────────────────
db.users.find //
db.users.find({ age: { $gt: 25 } }) //
db.users.findOne({ email: "alice@example.com" })

//
db.users.find({}, { name: 1, email: 1, _id: 0 })

// ··
db.users.find().sort({ age: -1 }).limit(10).skip(20)

// ── Update ──────────────────────────────────────
db.users.updateOne(
  { email: "alice@example.com" },
  { $set: { age: 31 }, $push: { tags: "editor" } }
)

db.users.updateMany(
  { age: { $lt: 18 } },
  { $set: { status: "minor" } }
)

// upsert
db.users.updateOne(
  { email: "dave@example.com" },
  { $set: { name: "Dave" } },
  { upsert: true }
)

// ── Delete ──────────────────────────────────────
db.users.deleteOne({ email: "bob@example.com" })
db.users.deleteMany({ status: "inactive" })

// compare
{ age: { $gt: 25, $lte: 40 } } // 25 40
{ status: { $in: ["active", "pending"] } }
{ status: { $nin: ["banned"] } }

//
{ $and: [{ age: { $gt: 20 } }, { age: { $lt: 40 } }] }
{ $or: [{ name: "Alice" }, { name: "Bob" }] }

//
{ tags: "admin" } //
{ tags: { $all: ["admin", "active"] } }

//
{ name: { $regex: /^Al/i } }

//
db.users.createIndex({ email: 1 }, { unique: true })

//
db.users.createIndex({ age: -1, name: 1 })

// TTL (30 after )
db.sessions.createIndex({ createdAt: 1 }, { expireAfterSeconds: 2592000 })

// list
db.users.getIndexes()

// run
db.users.find({ email: "alice@example.com" }).explain("executionStats")

//
db.users.aggregate([
 { $match: { status: "active" } }, //
  { $group: {
    _id: "$department",
    avgAge: { $avg: "$age" },
    count: { $sum: 1 }
  }},
  { $sort: { count: -1 } },
  { $limit: 5 }
])

// $lookup —
db.orders.aggregate([
  { $lookup: {
    from: "users",
    localField: "userId",
    foreignField: "_id",
    as: "user"
  }},
  { $unwind: "$user" },
  { $project: { orderId: 1, "user.name": 1, total: 1 } }
])

# backup
mongodump --out /backup/$(date +%Y%m%d)

# DB backup
mongodump --db mydb --out /backup/

# 
mongorestore /backup/20250527/

# 
mongodump --db mydb --collection users --out /backup/
mongorestore --db mydb --collection users /backup/mydb/users.bson