1. What is MongoDB?
MongoDB is a NoSQL database that stores data in documents that look like JSON instead of tables.
Example:
// Traditional SQL table
| id | name | age |
|----|------|-----|
| 1 | John | 25 |
// MongoDB document
{
"_id": ObjectId("..."),
"name": "John",
"age": 25
}2. What is a document in MongoDB?
A document is like a row in a table, but it can have different fields. It’s stored in JSON-like format called BSON.
Example:
// Document 1
{
"_id": ObjectId("..."),
"name": "Alice",
"age": 30,
"email": "alice@email.com"
}
// Document 2 (different fields)
{
"_id": ObjectId("..."),
"name": "Bob",
"age": 25,
"skills": ["JavaScript", "Python"]
}3. What is a collection in MongoDB?
A collection is like a table in SQL databases. It holds many documents of similar type.
Example:
// Collection: "users"
[
{ _id: 1, name: "Alice", age: 30 },
{ _id: 2, name: "Bob", age: 25 },
{ _id: 3, name: "Charlie", age: 35 },
];4. What is the difference between SQL and NoSQL?
SQL uses tables with fixed columns. NoSQL uses flexible documents that can have different fields.
Example:
// SQL (fixed structure)
CREATE TABLE users (
id INT,
name VARCHAR(50),
age INT
);
// NoSQL (flexible structure)
{ "name": "Alice", "age": 30, "email": "alice@email.com" }
{ "name": "Bob", "skills": ["JS", "Python"] }5. How do you create a database in MongoDB?
Use the command: use database_name. MongoDB creates it when you insert the first document.
Example:
use mystore
// Database "mystore" will be created when first document is inserted
db.products.insertOne({name: "Laptop", price: 999})6. How do you insert a document in MongoDB?
Use insertOne() for one document or insertMany() for multiple documents.
Example:
// Insert one document
db.users.insertOne({
name: "Alice",
age: 30,
email: "alice@email.com",
});
// Insert multiple documents
db.users.insertMany([
{ name: "Bob", age: 25 },
{ name: "Charlie", age: 35 },
]);7. How do you find documents in MongoDB?
Use find() to get all documents or findOne() to get the first matching document.
Example:
// Find all documents
db.users.find();
// Find specific documents
db.users.find({ age: 30 });
// Find one document
db.users.findOne({ name: "Alice" });8. What is _id in MongoDB?
_id is a unique identifier that MongoDB automatically creates for every document.
Example:
// Auto-generated _id
{
"_id": ObjectId("507f1f77bcf86cd799439011"),
"name": "Alice",
"age": 30
}
// Custom _id
db.users.insertOne({
"_id": "user001",
"name": "Bob",
"age": 25
})9. How do you update documents in MongoDB?
Use updateOne() to update one document or updateMany() to update multiple documents.
Example:
// Update one document
db.users.updateOne({ name: "Alice" }, { $set: { age: 31 } });
// Update multiple documents
db.users.updateMany({ age: { $lt: 30 } }, { $set: { status: "young" } });10. How do you delete documents in MongoDB?
Use deleteOne() to delete one document or deleteMany() to delete multiple documents.
Example:
// Delete one document
db.users.deleteOne({ name: "Alice" });
// Delete multiple documents
db.users.deleteMany({ age: { $lt: 18 } });