MongoDB
Introduction
• MongoDB is a NoSQL, document-oriented database.
• Stores data in JSON.
• Schema-less: documents can have different structures.
Basic Terminology
RDBMS MongoDB
Database Database
Table Collection
Row Document
Column Field
MongoDB Data Types
• String, Number (Int, Long, Double), Boolean
• Array
• Object (Embedded documents)
• Date
• Null
• ObjectId (Unique identifier)
Collection Commands
db.createCollection("students") # Create collection
show collections # List collections
db.students.drop() # Drop collection
Document Commands
// Insert
db.students.insertOne({ name: "John", age: 22, course: "MERN" })
db.students.insertMany([{ name: "A" }, { name: "B" }])
// Read
db.students.find()
db.students.find({ age: { $gt: 18 } })
// Update
db.students.updateOne({ name: "John" }, { $set: { age: 23 } })
db.students.updateMany({}, { $set: { active: true } })
// Delete
db.students.deleteOne({ name: "John" })
db.students.deleteMany({ active: false })
MongoDB Query Operators
There are many query operators that can be used to compare and reference document fields.
Comparison
The following operators can be used in queries to compare values:
• $eq : Values are equal
• $ne : Values are not equal
• $gt : Value is greater than another value
• $gte : Value is greater than or equal to another value
• $lt : Value is less than another value
• $lte : Value is less than or equal to another value
• $in : Value is matched within an array
$in Syntax :
{ field: { $in: [value1, value2, ...] } }
Example 1: Match students with course in a list
db.students.find({
course: { $in: ["Web", "MERN"] }
})
This will return all students whose course is either "Web" or "MERN".
Example 2: Match a value within an array field:
{
name: "Ankit",
skills: ["HTML", "CSS", "JavaScript"]
}
To find students who have "CSS" in their skills array:
db.students.find({
skills: { $in: ["CSS"] }
})
Logical
The following operators can logically compare multiple queries.
• $and : Returns documents where both queries match
• $or : Returns documents where either query matches
• $not : Returns documents where the query does not match
$and Syntax:
{
$and: [
{ field1: condition1 },
{ field2: condition2 }
]
}
Example: Find students with age > 20 and course = "Web"
db.students.find({
$and: [
{ age: { $gt: 20 } },
{ course: "Web" }
]
})
This will return only those students who are:
• Older than 20
• Enrolled in the "Web" course
Shortcut:
MongoDB treats multiple conditions in a single object as an implicit $and. So, this works the same:
db.students.find({
age: { $gt: 20 },
course: "Web"
})
$or Syntax :
{ $or: [ { condition1 }, { condition2 } ] }
Example:
Find students who are younger than 20 OR enrolled in "MERN":
db.students.find({
$or: [
{ age: { $lt: 20 } },
{ course: "MERN" }
]
})
$not – Inverts the Condition :
Example:
Find students whose age is NOT greater than 20:
db.students.find({
age: { $not: { $gt: 20 } }
})
MongoDB Practice Set
Task 1: Basic CRUD
1. Create a database called school.
2. Create a collection called students.
3. Insert 5 documents with fields: name, age, course, city.
4. Find all students from city "Delhi".
5. Update age of student named "Amit" to 25.
6. Delete student whose name is "Ravi".
Task 2: Advanced Queries
1. Find students with age > 20 and course = "Web".
2. Find students who are not from "Delhi".
3. Add a new field isActive: true to all documents.
Task 3: Array Operations
1. Add a field skills as an array: ["HTML", "CSS"]
2. Find students who know "CSS".
3. Add "JavaScript" to the skills array of one student.
MongoDB Update Operators
• $currentDate: Sets the field value to the current date
• $inc: Increments the field value
• $rename: Renames the field
• $set: Sets the value of a field
• $unset: Removes the field from the document
Syntax:
db.collection.updateOne(
{ /* filter */ },
{ $currentDate: { fieldName: true } }
)
Or if you want a timestamp instead of just a date:
$currentDate: { fieldName: { $type: "timestamp" } }
Example 1: Add a lastUpdated field with current date
db.students.updateOne(
{ name: "Amit" },
{ $currentDate: { lastUpdated: true } }
)
This will add:
"lastUpdated": ISODate("2025-04-09T12:34:56.000Z")
Example 2: Add a lastLogin timestamp
db.students.updateOne(
{ name: "Ravi" },
{ $currentDate: { lastLogin: { $type: "timestamp" } } }
)
Connect Mongodb With Node.Js
Using Mongoose
1. Install Mongoose
npm install mongoose
2. Connect to MongoDB
const mongoose = require('mongoose');
mongoose.connect('mongodb://localhost:27017/mydatabase', {
useNewUrlParser: true,
useUnifiedTopology: true
})
.then(() => console.log("MongoDB connected successfully"))
.catch((err) => console.error("MongoDB connection error:", err));
Replace mydatabase with your DB name. Use mongodb+srv://... URI if connecting to MongoDB Atlas.
3. Create a Schema and Model
const userSchema = new mongoose.Schema({
name: String,
email: String,
age: Number
});
const User = mongoose.model('User', userSchema);
// Example: Create a new user
const newUser = new User({ name: "Deepak", email: "deepak@example.com", age: 25 });
newUser.save().then(() => console.log("User saved"));
useNewUrlParser: true
Setting useNewUrlParser: true tells Mongoose to use the new, modern connection string parser.
Required when using connection strings for things like MongoDB Atlas (e.g., with multiple hosts,
options, credentials).
useUnifiedTopology: true
Improves the way Mongoose manages connections, monitoring, and failover.
configure MongoDB Atlas
Step 1: Create MongoDB Atlas Account
1. Go to https://www.mongodb.com/cloud/atlas
2. Sign up (or log in if you already have an account)
Step 2: Create a Cluster
1. Click on "Build a Database"
2. Choose a free tier if you're just getting started
3. Select:
o Cloud provider (AWS, GCP, or Azure)
o Region (preferably near your location)
4. Click "Create Cluster"
Step 3: Create Database User
1. Go to Database Access in the sidebar
2. Click "Add New Database User"
3. Set a username and password
4. Give Read and Write access to any database
5. Click "Add User"
Step 4: Whitelist Your IP
1. Go to Network Access from the sidebar
2. Click "Add IP Address"
3. Choose "Allow Access from Anywhere" (for dev use) → 0.0.0.0/0
4. Or enter your specific IP address
5. Click "Confirm"
Step 5: Create a Database & Collection
1. Go to Database > Clusters
2. Click "Browse Collections"
3. Click "Add My Own Data"
4. Enter:
o Database name (e.g., myAppDB)
o Collection name (e.g., users)
Step 6: Connect Your Application
1. Go to Clusters > Connect > Connect Your Application
2. Copy the Connection String (looks like this):
mongodb+srv://<username>:<password>@cluster0.mongodb.net/<dbname>?retryWrites=true&w=
majority
Replace:
• <username> with your DB username
• <password> with your DB password
• <dbname> with your database name
Step 7: Use It in Your Code (Example in Node.js)
const mongoose = require('mongoose');
mongoose.connect(
'mongodb+srv://<username>:<password>@cluster0.mongodb.net/myAppDB?retryWrites=true&w=
majority',
{
useNewUrlParser: true,
useUnifiedTopology: true,
}
).then(() => {
console.log("Connected to MongoDB Atlas");
}).catch(err => {
console.error("Error connecting to MongoDB Atlas", err);
});
Step-by-Step Guide to Add MongoDB URL in .env
1. Install dotenv package
npm install dotenv
2. Create a .env file in the root of your project:
MONGO_URL=mongodb://localhost:27017/mydatabase
3. Update index.js to use .env
require('dotenv').config();
Then update your mongoose.connect line like this:
mongoose.connect(process.env.MONGO_URL, {
useNewUrlParser: true,
useUnifiedTopology: true
})
.then(() => console.log("MongoDB connected successfully"))
.catch((err) => console.error("MongoDB connection error:", err));
Final index.js Snippet (first few lines):
require('dotenv').config(); // Load .env variables
const express = require('express');
const app = express();
const cors = require('cors');
const mongoose = require('mongoose');
const PORT = 5000;
app.use(cors());
app.use(express.json());
mongoose.connect(process.env.MONGO_URL, {
useNewUrlParser: true,
useUnifiedTopology: true
})
.then(() => console.log("MongoDB connected successfully"))
.catch((err) => console.error("MongoDB connection error:", err));
4. Don’t forget to add .env to .gitignore
In your .gitignore file, add:
.env
Modified userSchema with createdAt and updatedAt:
const userSchema = new mongoose.Schema({
name: String
}, {
timestamps: true // This adds createdAt and updatedAt fields automatically
});
Full Updated Section in Your Code:
const userSchema = new mongoose.Schema({
name: String
}, {
timestamps: true // Automatically manages createdAt and updatedAt
});
const User = mongoose.model('users', userSchema);
Now, every document in the users collection will have:
{
"_id": "...",
"name": "John Doe",
"createdAt": "2025-04-10T08:30:00.000Z",
"updatedAt": "2025-04-10T08:30:00.000Z",
"__v": 0
}
