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🍃 MongoDB Essentials: CLI, Configuration, Users, and Data Modeling

MongoDB is a flexible NoSQL document-oriented database popular for rapid development and scalable systems. This guide covers the MongoDB shell (mongosh), server configuration, user access, data modeling, indexing, and performance insights.

🧑‍💻 1. Using the MongoDB Shell (mongosh)

🔹 Connecting to MongoDB

mongosh
mongosh "mongodb://localhost:27017"
mongosh "mongodb://user:pass@localhost:27017/admin"

🔹 Common Shell Commands

show dbs
use mydb
show collections
db.users.find()
exit

MongoDB uses JavaScript syntax for shell queries.

⚙️ 2. Configuration for Production

🔹 Config File Location

Typical file: /etc/mongod.conf

Example config for a secure server:

net:
  port: 27017
  bindIp: 127.0.0.1

security:
  authorization: enabled

storage:
  dbPath: /var/lib/mongodb

systemLog:
  destination: file
  path: /var/log/mongodb/mongod.log
  logAppend: true

🔹 Managing the Service

# Debian-based
sudo systemctl restart mongod
sudo systemctl status mongod

👤 3. User and Role Management

🔹 Create Admin User

use admin
db.createUser({
  user: "admin",
  pwd: "securepass",
  roles: [ { role: "userAdminAnyDatabase", db: "admin" } ]
})

🔹 Create Application User

use mydb
db.createUser({
  user: "appuser",
  pwd: "app123",
  roles: [ { role: "readWrite", db: "mydb" } ]
})

🔹 List and Drop Users

db.getUsers()
db.dropUser("appuser")

📦 4. MongoDB Documents & Collections

🔹 Insert and Query Documents

db.users.insertOne({ name: "Jane", age: 30, active: true })
db.users.find({ age: { $gte: 18 } })

🔹 Update and Delete

db.users.updateOne({ name: "Jane" }, { $set: { age: 31 } })
db.users.deleteMany({ active: false })

MongoDB is schema-less, but good design matters.

📐 5. Data Modeling in MongoDB

Strategy Description Example Use Case
Embedding Store related data in the same document Blog post with comments
Referencing Store relations via ObjectId references User references roles or profiles
Denormalization Copy data across documents for performance Order with duplicated user info

🔹 Embedded Example

{
  _id: ObjectId("..."),
  title: "Post Title",
  comments: [
    { user: "A", text: "Nice!" },
    { user: "B", text: "Cool!" }
  ]
}

⚡ 6. Indexing for Performance

🔹 Creating and Listing Indexes

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

🔹 Compound and TTL Indexes

db.logs.createIndex({ createdAt: 1 }, { expireAfterSeconds: 3600 })

Use indexes wisely to speed up reads, but avoid over-indexing.

🛡️ 7. Security Best Practices

🛠️ 8. Maintenance & Tools

🔹 Backup and Restore

# Backup
mongodump --db=mydb --out=/backups/mydb

# Restore
mongorestore --db=mydb /backups/mydb

🔹 Monitoring

Use:

db.serverStatus()
db.stats()

Or external tools:

🚀 9. Advanced Concepts

🔹 Aggregation Framework

db.orders.aggregate([
  { $match: { status: "shipped" } },
  { $group: { _id: "$customerId", total: { $sum: "$amount" } } }
])

🔹 Transactions (Replica Set required)

const session = db.getMongo().startSession()
session.startTransaction()
session.getDatabase("mydb").users.updateOne({ id: 1 }, { $inc: { balance: -100 } })
session.getDatabase("mydb").users.updateOne({ id: 2 }, { $inc: { balance: 100 } })
session.commitTransaction()
session.endSession()

Full ACID transactions are supported only in replica sets or sharded clusters.

📚 Resources

✅ Summary

Task Tool/Command
Connect mongosh
Create DB/User db.createUser()
Insert/Query db.collection.find(), insertOne()
Indexing createIndex(), getIndexes()
Security auth, bindIp, roles, password
Backup/Restore mongodump, mongorestore
Monitor db.stats(), db.serverStatus()
Transactions startSession(), commitTransaction()
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