MongoDB Shell Crash Course

Table of Contents

Introduction

MongoDB is a popular NoSQL database that stores data in flexible, JSON-like documents. This structure allows for dynamic schemas, making it a preferred choice for modern applications that require scalability and performance.

Prerequisites

• Node.js: Ensure you have Node.js installed on your system. You can download it from the official website.

1. Start the MongoDB Server: Run the following command to start the MongoDB server:

   mongod
   

   By default, MongoDB listens on port 27017.

2. Access the MongoDB Shell: Open a new terminal window and execute:

   mongosh
   

   This command opens the MongoDB shell, allowing you to interact with your databases.

Understanding MongoDB

Databases and Collections

• Database: A container for collections. Each database gets its own set of files on the file system.
• Collection: A group of MongoDB documents, akin to a table in relational databases.

Documents

Documents are the basic units of data in MongoDB, stored in a format called BSON (Binary JSON). An example document:

{
  "_id": ObjectId("507f1f77bcf86cd799439011"),
  "name": "John Doe",
  "age": 29,
  "email": "johndoe@example.com",
  "address": {
    "street": "123 Main St",
    "city": "Anytown",
    "state": "CA",
    "zip": "12345"
  }
}

Basic CRUD Operations

1. Create (Insert)

To add a new document to a collection:

db.users.insertOne({
  "name": "Jane Smith",
  "age": 32,
  "email": "janesmith@example.com"
});

2. Read (Find)

Retrieve documents from a collection:

// Find all documents
db.users.find();

// Find documents with a specific condition
db.users.find({ "age": 30 });

3. Update

Modify existing documents:

// Update a single document
db.users.updateOne(
  { "name": "Jane Smith" },
  { $set: { "age": 33 } }
);

// Update multiple documents
db.users.updateMany(
  { "age": { $lt: 25 } },
  { $set: { "status": "Underage" } }
);

4. Delete

Remove documents from a collection:

// Delete a single document
db.users.deleteOne({ "name": "Jane Smith" });

// Delete multiple documents
db.users.deleteMany({ "status": "Underage" });

Indexes

Indexes support the efficient execution of queries. Without indexes, MongoDB must perform a collection scan, i.e., scan every document in a collection, to select those documents that match the query statement.

Creating an Index

// Create an index on the 'email' field
db.users.createIndex({ "email": 1 });

Viewing Indexes

// List all indexes on the 'users' collection
db.users.getIndexes();

Aggregation

Aggregation operations process data records and return computed results. They are useful for operations such as grouping values from multiple documents or performing operations on grouped data.

Example: Aggregation Pipeline

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