MongoDB

Junghoo Cho

cho@cs.ucla.edu

MongoDB

• Database for JSON objects
  • “NoSQL database”
• Schema-less: no predefined schema
  • MongoDB will store anything with no complaint!
  • No normalization or joins
  • Use Mongoose for ensuring structure in the data
• Adopts JavaScript philosophy
  • “Laissez faire” policy
    • Don’t be too strict! Handle user request in a “reasonable” way
  • Both blessing and curse

Document in MongoDB (1)

• Data is stored as a collection of documents
  • Document: (almost) JSON object
  • Collection: group of “similar” documents
• Example

  { 
      "_id": ObjectId(8df38ad8902c),
      "title": "MongoDB", 
      "description": "MongoDB is NoSQL database", 
      "tags": ["mongodb", "database", "NoSQL"], 
      "likes": 100, 
      "comments": [ 
          { "user":"lover", "comment": "Great book!" }, 
          { "user":"hater", "comment": "Worst ever!" }]
  }
  

Document in MongoDB (2)

• Stored as BSON (Binary representation of JSON)
  • Supports more data types than JSON
  • Does not require double quotes for field names
• _id field: primary key
  • Its value must be unique in the collection
  • May be of any type other than array
  • If not provided, _id is automatically added with a unique ObjectId value
• Analogy
  • Document in MongoDB ≃ row in RDB
  • Collection in MongoDB ≃ table in RDB

MongoDB vs RDB

MongoDB Demo

show dbs;
use demo;
show collections;
db.books.insertOne({title: "MongoDB", likes: 100});
db.books.find();
show collections;
show dbs;
db.books.insertMany([{title: "a"}, {title: "b"}]);
db.books.find();
db.books.find({likes: 100});
db.books.find({likes: {$gt: 10}});
db.books.updateOne({title: "MongoDB"}, {$set: { likes: 200 }});
db.books.find();
db.books.deleteOne({title: "a"});
db.books.drop();
show collections;
show dbs;

Basic MongoDB Commands (1)

• mongo: start MongoDB shell
• use <dbName>: use the database
• show dbs: show list of databases
• show collections: show list of collections
• db.colName.drop(): delete colName collection
• db.dropDatabase(): delete current database

Basic MongoDB Commands (2)

• CRUD operations
  • Create: insertOne(), insertMany()
  • Retrieve: findOne(), find()
  • Update: updateOne(), updateMany()
  • Delete: deleteOne(), deleteMany()

Basic MongoDB Commands (3)

• 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, …

Basic MongoDB Commands (4)

• 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}})
  

Basic MongoDB Commands (4)

• Indexes can be built for efficient retrieval
• db.books.createIndex({title:1, likes:-1})
  • Create one index on combined attributes “title” and “likes”
  • 1 means ascending order, -1 means descending order

More on MongoDB

• We learned just the basic
  • Enough for our project
• But MongoDB has many more features:
  • Aggreate queries
  • Transactions
  • Replication
  • (Auto)sharding
  • …
• Read MongoDB documentation and online tutorials to learn more