Node.jsスクリプトによるデータのシード

Why Write a Seed Script?

Setting Up the MongoDB Client

const { MongoClient, ObjectId } = require('mongodb');

const URI = process.env.MONGO_URI || 'mongodb://localhost:27017';
const DB_NAME = 'myapp';

async function seed() {
  const client = new MongoClient(URI);
  try {
    await client.connect();
    console.log('Connected to MongoDB');
    const db = client.db(DB_NAME);
    await seedUsers(db);
    await seedProducts(db);
    console.log('Seeding complete!');
  } finally {
    await client.close();
  }
}

seed().catch(console.error);

Inserting Documents With bulkWrite

async function seedUsers(db) {
  const users = [
    { _id: new ObjectId('aaa000000000000000000001'), name: 'Alice', email: 'alice@example.com', role: 'admin' },
    { _id: new ObjectId('aaa000000000000000000002'), name: 'Bob',   email: 'bob@example.com',   role: 'user'  },
    { _id: new ObjectId('aaa000000000000000000003'), name: 'Carol', email: 'carol@example.com', role: 'user'  }
  ];

  const ops = users.map(u => ({ insertOne: { document: u } }));
  const result = await db.collection('users').bulkWrite(ops, { ordered: false });
  console.log('Users inserted:', result.insertedCount);
}

Idempotent Seeding With deleteMany

async function seedProducts(db) {
  const col = db.collection('products');

  // Clear existing data first — idempotent
  await col.deleteMany({});
  console.log('Cleared products collection');

  const products = generateProducts(50); // generate 50 sample products
  await col.insertMany(products);
  console.log('Inserted', products.length, 'products');
}

Generating Realistic Fake Data

function generateProducts(count) {
  const categories = ['electronics', 'clothing', 'tools', 'books'];
  return Array.from({ length: count }, (_, i) => ({
    _id: new ObjectId(),
    sku: 'PROD-' + String(i + 1).padStart(4, '0'),
    name: 'Product ' + (i + 1),
    price: parseFloat((Math.random() * 100 + 1).toFixed(2)),
    category: categories[i % categories.length],
    rating: parseFloat((Math.random() * 2 + 3).toFixed(1)), // 3.0 - 5.0
    isActive: true,
    createdAt: new Date(Date.now() - i * 86400000) // staggered dates
  }));
}

Seeding Relationships Between Collections

const USER_ID_ALICE = new ObjectId('aaa000000000000000000001');
const USER_ID_BOB   = new ObjectId('aaa000000000000000000002');

async function seedOrders(db) {
  await db.collection('orders').deleteMany({});
  const orders = [
    { userId: USER_ID_ALICE, total: 49.99,  status: 'delivered', createdAt: new Date() },
    { userId: USER_ID_BOB,   total: 120.00, status: 'pending',   createdAt: new Date() }
  ];
  await db.collection('orders').insertMany(orders);
  console.log('Orders seeded');
}

Reading Seed Data From JSON Files

const fs  = require('fs');
const path = require('path');

async function seedFromFile(db, collectionName, filePath) {
  const raw  = fs.readFileSync(path.resolve(filePath), 'utf-8');
  const docs = JSON.parse(raw);

  const col = db.collection(collectionName);
  await col.deleteMany({});
  await col.insertMany(docs);
  console.log('Seeded', docs.length, 'documents into', collectionName);
}

// Usage
await seedFromFile(db, 'countries', './seed-data/countries.json');

Creating Indexes After Seeding

async function ensureIndexes(db) {
  // Products: fast category lookups and rating sorts
  await db.collection('products').createIndex({ category: 1, rating: -1 });
  await db.collection('products').createIndex({ sku: 1 }, { unique: true });

  // Orders: fast user-based queries
  await db.collection('orders').createIndex({ userId: 1, createdAt: -1 });

  console.log('Indexes created');
}

Running the Seed Script

// package.json scripts
// {
//   "scripts": {
//     "seed": "node scripts/seed.js",
//     "seed:test": "MONGO_URI=mongodb://localhost:27017 node scripts/seed.js"
//   }
// }

// Run with:
// npm run seed
// or
// MONGO_URI='mongodb://localhost:27017' node scripts/seed.js

Using Seed Scripts in CI Pipelines

# GitHub Actions step example
# - name: Start MongoDB
#   run: docker run -d -p 27017:27017 mongo:7

# - name: Seed test data
#   run: node scripts/seed.js
#   env:
#     MONGO_URI: mongodb://localhost:27017

# - name: Run integration tests
#   run: npm test
#   env:
#     MONGO_URI: mongodb://localhost:27017

Handling Seed Errors Gracefully

async function seed() {
  const client = new MongoClient(process.env.MONGO_URI);
  try {
    await client.connect();
    const db = client.db('myapp');
    await seedUsers(db);
    await seedProducts(db);
    await seedOrders(db);
    await ensureIndexes(db);
    console.log('All seed steps completed successfully');
    process.exit(0);
  } catch (err) {
    console.error('Seed failed:', err.message);
    process.exit(1);
  } finally {
    await client.close();
  }
}

Quick Check

Lesson Recap