MongoDB

In one sentence, MongoDB is a database management system for JSON data.

RDBMS for JS Object Persistence

• JS applications need a "persistence layer" to store and retrive JavaScript object
• Traditionally(until mid 2010) this was done with RDBMS
• Q: How can we store JavaScript object in RDB?

MongoDB

• Databse for JSON objects
  • Perfect as a simple persistence layer for JavaScript objects
  • "NoSQL database"
• Data is stored as a collection of documents
  • Document: (almost) JSON object
  • Colletions: group of "similar" documents

Philosophy of MongoDB

• Adopts JavaScript "laissez faire" philosophy
  • Don't be too strict! Be accomodating! Handle user request in a "reasonable" way
• Schema-less: no predefined schema
  • Give me anything. I will store it anywhere you want
  • One collection will store documents of any kind with no complaint
• No need to "plan ahead"
  • A "database" is created when a first collection is created
  • A "collection" is created when a first document is inserted
• Both blessing and curse

Basic Commands:

mongo             #start
use <dbname>      #use that database
show dbs          #show list of databases
show collections  #show list of collections
db.colName.drop() #delete colName collection
db.dropDatabase() #delete current database

#CRUD Operation
Create: insertOne(), insertMany()
Retrieve: findOne(), find()
Update: updateOne(), updateMany()
Delete: deleteOne(), deleteMany()
#if there's multiple values,the system would choose a random one to update/delete

CRUD Operations

# Create: insertX(doc(s))
db.books.insertOne({title: "MongoDB", likes: 100})
db.books.insertMany([{title: "a"}, {title: "b"}])

# Retrieve: findX(condition)
db.books.findOne({likes: 100})
db.books.find({$and: [{likes: {$gte: 10}}, {likes: {$lt: 20}}]})
# findOne() returns the first (?) matching document for multiple matches
# Other boolean/comparison operators: $or, $not, $gt, $ne, …

# Update: updateX(condition, update_op)
db.books.updateOne({title: "MongoDB"}, {$set: {title: "MongoDB II"}})
db.books.updateMany({title: "MongoDB"}, {$inc: {likes: 1}})
# Other update operators: $mul (multiply), $unset (remove the field), …

# Delete: deleteX(condition)
db.books.deleteOne({title: "MongoDB"})
db.books.deleteMany({likes: {$lt: 100}}

MongoDB Aggregates