const { MongoClient } = require('mongodb');
const client = new MongoClient(process.env.MONGO_URI);
const db = client.db('ecommerce');
const products = db.collection('products');
 
// INSERT a document with flexible schema
await products.insertOne({
  name: 'Wireless Headphones'Headphones',
  price: 79.99,
  category: 'electronics',
  specs: { battery: '30h', connectivity: 'Bluetooth 5.0'5.0' },
  tags: ['wireless', 'audio', 'portable'],
  inStock: true
});
 
// FIND with filters, projection, and sorting
const results = await products.find(
  { category: 'electronics', price: { $lt: 100 }, inStock: true },
  { projection: { name: 1, price: 1, _id: 0 } }  // return only name and price
).sort({ price: 1 }).limit(10).toArray();
 
// UPDATE: add a field or modify existing
await products.updateMany(
  { category: 'electronics' },
  { $set: { taxRate: 0.08 }, $inc: { viewCount: 1 } }
);
 
// AGGREGATION PIPELINE (MongoDB's equivalent of SQL GROUP BY + JOIN)PIPELINE (MongoDB's equivalent of SQL GROUP BY + JOIN)
const salesByCategory = await products.aggregate([
  { $match: { inStock: true } },
  { $group: { _id: '$category', count: { $sum: 1 }, avgPrice: { $avg: '$price' } } },
  { $sort: { count: -1 } }
]).toArray();

const redis = require('redis');
const client = redis.createClient({ url: process.env.REDIS_URL });
await client.connect();
 
// Cache-aside pattern: check Redis first, fallback to DBRedis first, fallback to DB
async function getUser(userId) {
  const cacheKey = `user:${userId}`}`;
  
  // Check cache first
  const cached = await client.get(cacheKey);
  if (cached) return JSON.parse(cached);
  
  // Miss: fetch from DB, store in cacheDB, store in cache
  const user = await db.query('SELECT * FROM users WHERE id = ?'FROM users WHERE id = ?', [userId]);
  await client.setEx(cacheKey, 3600, JSON.stringify(user));  // expire in 1hr
  return user;
}
 
// Real-time leaderboard with sorted sets
await client.zAdd('game:leaderboard', [
  { score: 1500, value: 'alice' },
  { score: 2300, value: 'bob' },
  { score: 1800, value: 'charlie' }
]);
 
// Get top 10 players10 players
const topPlayers = await client.zRangeWithScores('game:leaderboard', 0, 9, { REV: true });
 
// Session storage with automatic expiry
await client.setEx(`session:${sessionId}`}`, 1800, JSON.stringify(sessionData));
 
// Atomic counter (no race conditions)(no race conditions)
await client.incr(`page:${pageId}:views`}:views`);