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MongoDB Basics

Connection & Database Operations​

# Connect to MongoDB
mongosh "mongodb://localhost:27017"

# Show databases
show dbs

# Use/create database
use mydb

# Show collections
show collections

# Database stats
db.stats()

Basic CRUD Operations​

Insert Documents​

// Insert single document
db.users.insertOne({
  name: "John Doe",
  email: "john@example.com",
  age: 30
});

// Insert multiple documents
db.users.insertMany([
  { name: "Alice", email: "alice@example.com", age: 25 },
  { name: "Bob", email: "bob@example.com", age: 35 }
]);

Find Documents​

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

// Find with condition
db.users.find({ age: { $gte: 30 } });

// Find one document
db.users.findOne({ email: "john@example.com" });

// Pretty print
db.users.find().pretty();

// Limit results
db.users.find().limit(5);

// Sort results
db.users.find().sort({ age: -1 });

Update Documents​

// Update single document
db.users.updateOne(
  { email: "john@example.com" },
  { $set: { age: 31 } }
);

// Update multiple documents
db.users.updateMany(
  { age: { $lt: 30 } },
  { $set: { status: "young" } }
);

// Upsert (update or insert)
db.users.updateOne(
  { email: "new@example.com" },
  { $set: { name: "New User", age: 25 } },
  { upsert: true }
);

Delete Documents​

// Delete single document
db.users.deleteOne({ email: "john@example.com" });

// Delete multiple documents
db.users.deleteMany({ age: { $lt: 18 } });

// Drop collection
db.users.drop();

Document Structure​

// Flexible document example
{
  _id: ObjectId("..."),
  name: "John Doe",
  email: "john@example.com",
  profile: {
    age: 30,
    location: "San Francisco",
    interests: ["coding", "music"]
  },
  createdAt: new Date(),
  isActive: true
}

Common Data Types​

{
  _id: ObjectId("..."),           // ObjectId
  string: "text",                 // String
  number: 42,                     // Number (Int32/Int64/Double)
  decimal: NumberDecimal("99.99"), // Decimal128
  boolean: true,                  // Boolean
  date: new Date(),               // Date
  array: [1, 2, 3],              // Array
  object: { key: "value" },       // Object
  null: null,                     // Null
  regex: /pattern/i               // Regular Expression
}