mongodb.md

sql databases

MongoDB

NoSQL document-based database

• stores data in JSON-like documents
  • e.g. { "name": "John", "age": 30 }
• schema-less, each document can have a different structure
• scales horizontally
• default port is 27017
• mongosh: official CLI used to interact with MongoDB databases
  • replaced the older shell (mongo) since MongoDB 5.0+
  • used to:
    • connect to MongoDB server
    • run database commands using javascript
    • query and modify data
    • manage databases

MongoDB	relational DB
Documents	Rows
Collections	Tables
Fields	Columns
Schema-less	Predefined schema
Horizontal scaling	Mostly vertical
Good for nested data	Requires JOINs

document example in MongoDB:

{
  "name": "Alice",
  "age": 25,
  "email": "alice@example.com"
}

• "name", "age" and "email" are fields
• this whole object is a document
• it belongs to a collection

CLI commands

• connect to mongodb: mongosh

• connect to mongodb with connection string: mongosh "mongodb://<host>:<port>/<database>"

• show all database: show dbs

• show current database: db

• use or create a database: use mydb

• list running databases and their stats: db.stats()

• drop/delete a database: db.dropDatabase()

• show all collections: show collections

• create a collection manually: db.createCollection("myCollection")

• drop/delete a collection: db.myCollection.drop()

• create/insert a document: db.users.insertOne({ name: "Alice", age: 30 })

  • this command automatically create the users collection if it doesn't exist

• find a document: db.users.find({ name: "Alice" })

• delete a document: db.users.deleteOne({ name: "Alice" })

• delete many documents: db.myCollection.deleteMany({ age: { $lt: 30 } })

• find all documents: db.myCollection.find()

  • pretty-print results: db.myCollection.find().pretty()
  • limit number of results: db.myCollection.find().limit()
  • sort results: db.myCollection.find().sort()

• find first match of a document: db.myCollection.findOne({ name: "Alice" })

• find document with filters: db.myCollection.find({ age: { $gt: 25 } }) // age > 25

• update document: db.myCollection.updateOne( { name: "Alice" }, { $set: { age: 31 } })

• count documents: db.myCollection.countDocuments()

insert many documents:

db.myCollection.insertMany([
  { name: "Bob", age: 30 },
  { name: "Charlie", age: 28 }
])

update many documents:

db.myCollection.updateMany(
  { age: { $gt: 25 } },
  { $set: { status: "senior" } }
)

• export/dump a database: mongodump --db nome_do_banco --out ~/backups/mongodb
• import/restore a database: mongorestore --db nome_do_banco_novo /caminho/do/backup/nome_do_banco_original