Introduction to MongoDB

MongoDB is a NoSQL document-oriented database that stores data in JSON-like BSON format.

MongoDB Basics

Databases & Collections

-- Show all databases
show dbs;

-- Create / Switch Database
use School;

-- Show all collections
show collections;

-- Create Collection
db.createCollection("Students");
      

CRUD Operations

-- Insert Document
db.Students.insertOne({Name:"John", Age:15, Grade:"10th"});

-- Insert Multiple Documents
db.Students.insertMany([{Name:"Jane", Age:16},{Name:"Mike", Age:17}]);

-- Find Documents
db.Students.find();
db.Students.find({Age:16});

-- Update Document
db.Students.updateOne({Name:"John"}, {$set:{Age:16}});

-- Delete Document
db.Students.deleteOne({Name:"John"});
      

MongoDB Queries

Filtering Documents

db.Students.find({Age: {$gt:15}});
db.Students.find({Grade:"10th"});
      

Sorting

db.Students.find().sort({Age:1});   // Ascending
db.Students.find().sort({Age:-1});  // Descending
      

Aggregations

db.Students.aggregate([
  {$match: {Age: {$gt:15}}},
  {$group: {_id:"$Grade", avgAge: {$avg:"$Age"}}}
]);
      

Indexes & Performance

-- Create Index
db.Students.createIndex({Name:1});

-- View Indexes
db.Students.getIndexes();
      

Explain Query

db.Students.find({Age:16}).explain();
      

Advanced MongoDB

Aggregation Pipeline

db.Orders.aggregate([
  {$match: {status:"Shipped"}},
  {$group: {_id:"$customerId", total: {$sum:"$amount"}}},
  {$sort: {total:-1}}
]);
      

Embedded Documents & Arrays

db.Students.insertOne({
  Name:"Alice",
  Courses:[{Name:"Math", Score:90},{Name:"Science", Score:85}]
});
db.Students.find({"Courses.Name":"Math"});
      

Transactions

const session = db.getMongo().startSession();
session.startTransaction();
db.Students.updateOne({Name:"John"}, {$set:{Age:17}}, {session});
session.commitTransaction();
session.endSession();
      

Views

db.createView("TeenStudents", "Students", [{$match:{Age:{$gte:13,$lte:19}}}]);
db.TeenStudents.find();