🍃 BD04 — MongoDB Fondamentaux

1. Introduction à MongoDB

MongoDB est une base de données NoSQL orientée documents. Les données sont stockées en BSON (Binary JSON) dans des collections, sans schéma fixe obligatoire.

Concepts clés

# Installation driver Node.js
npm install mongodb

# Connexion rapide
mongosh "mongodb://localhost:27017/myapp"

2. Documents & BSON

// Structure d'un document MongoDB
{
  _id: ObjectId("64a5f2c..."),
  name: "Alice Dupont",
  email: "alice@example.com",
  age: 28,
  tags: ["admin", "verified"],
  address: {
    street: "12 Rue de la Paix",
    city: "Paris",
    zip: "75001"
  },
  orders: [
    { orderId: 101, total: 49.99, date: ISODate("2024-01-15") }
  ],
  createdAt: ISODate("2024-01-01T00:00:00Z"),
  active: true
}

Types BSON : String, Integer (32/64-bit), Boolean, Double, Array, Object, ObjectId, Date, Null, Binary, Decimal128, Regular Expression.

3. CRUD

const { MongoClient, ObjectId } = require('mongodb');
const client = new MongoClient(process.env.MONGODB_URI);
await client.connect();
const db = client.db('myapp');
const users = db.collection('users');

// --- CREATE ---
// insertOne
const result = await users.insertOne({
  name: 'Bob Martin',
  email: 'bob@example.com',
  role: 'user',
  createdAt: new Date()
});
console.log(result.insertedId); // ObjectId

// insertMany
await users.insertMany([
  { name: 'Alice', email: 'alice@example.com' },
  { name: 'Charlie', email: 'charlie@example.com' }
]);

// --- READ ---
// findOne
const user = await users.findOne({ email: 'bob@example.com' });

// find avec filtres
const admins = await users
  .find({ role: 'admin', active: true })
  .sort({ name: 1 })
  .limit(20)
  .skip(0)
  .project({ name: 1, email: 1, _id: 0 })
  .toArray();

// findById
const byId = await users.findOne({ _id: new ObjectId('64a5f2c...') });

// --- UPDATE ---
// updateOne
await users.updateOne(
  { email: 'bob@example.com' },
  { $set: { role: 'admin', updatedAt: new Date() } }
);

// updateMany
await users.updateMany(
  { role: 'user' },
  { $set: { verified: false } }
);

// findOneAndUpdate (retourne le doc mis à jour)
const updated = await users.findOneAndUpdate(
  { _id: new ObjectId('...') },
  { $inc: { loginCount: 1 } },
  { returnDocument: 'after' }
);

// --- DELETE ---
await users.deleteOne({ _id: new ObjectId('...') });
await users.deleteMany({ active: false, createdAt: { $lt: new Date('2020-01-01') } });

4. Opérateurs de requête

Comparaison

// $eq, $ne, $gt, $gte, $lt, $lte, $in, $nin
await products.find({
  price: { $gte: 10, $lte: 100 },
  category: { $in: ['electronics', 'gaming'] },
  stock: { $gt: 0 }
}).toArray();

// $exists, $type
await users.find({ phone: { $exists: true, $ne: null } }).toArray();

Logiques

// $and, $or, $nor, $not
await products.find({
  $or: [
    { price: { $lt: 20 } },
    { featured: true }
  ]
}).toArray();

Tableaux

// $push, $addToSet, $pull, $pop
await users.updateOne(
  { _id: userId },
  { $addToSet: { tags: 'premium' } }  // ajoute si absent
);
await users.updateOne(
  { _id: userId },
  { $pull: { tags: 'trial' } }  // supprime
);

// $elemMatch
await orders.find({
  items: { $elemMatch: { productId: 'P001', qty: { $gte: 2 } } }
}).toArray();

Mise à jour

// $set, $unset, $inc, $mul, $rename, $currentDate
await products.updateOne(
  { _id: productId },
  {
    $set: { name: 'New Name' },
    $inc: { stock: -1, viewCount: 1 },
    $currentDate: { updatedAt: true }
  }
);

5. Index MongoDB

// Index simple
await users.createIndex({ email: 1 }, { unique: true });

// Index composé
await orders.createIndex({ userId: 1, createdAt: -1 });

// Index text (full-text search)
await articles.createIndex(
  { title: 'text', body: 'text' },
  { weights: { title: 10, body: 1 }, default_language: 'french' }
);

// Recherche full-text
await articles.find({ $text: { $search: 'postgresql index' } })
  .sort({ score: { $meta: 'textScore' } })
  .toArray();

// Index TTL (expiration automatique)
await sessions.createIndex({ expiresAt: 1 }, { expireAfterSeconds: 0 });

// Index sparse (ignore les docs sans le champ)
await users.createIndex({ phone: 1 }, { sparse: true });

// Lister les index
await users.listIndexes().toArray();

// Supprimer un index
await users.dropIndex('email_1');

6. Design de schéma

Embedding vs Références

// Embedding (1-to-few) — adresse dans user
{ _id: ..., name: 'Alice', address: { street: '...', city: 'Paris' } }

// Référence (1-to-many) — orders dans collection séparée
{ _id: ..., userId: ObjectId('...'), total: 49.99, items: [...] }