Data Seeding Skill

Seed scripts live in packages/database/src/seed/ .

Running Seeds

pnpm -F @sgcarstrends/database db:seed # Run all seeds pnpm -F @sgcarstrends/database db:seed:cars # Seed specific table

Basic Seed Pattern

// packages/database/src/seed/cars.ts import { db } from "../index"; import { cars } from "../db/schema"; import { nanoid } from "nanoid";

export async function seedCars() { console.log("Seeding cars...");

const carData = [ { id: nanoid(), make: "Toyota", model: "Camry", vehicleClass: "Sedan", fuelType: "Petrol", month: "2024-01", number: 150 }, { id: nanoid(), make: "Honda", model: "Civic", vehicleClass: "Sedan", fuelType: "Petrol", month: "2024-01", number: 120 }, ];

await db.insert(cars).values(carData); console.log(Seeded ${carData.length} cars); }

Main Seed Runner

// packages/database/src/seed/index.ts export async function seed() { console.log("Starting database seed...");

await clearDatabase(); // Optional: clear existing data await seedCars(); await seedCOE(); await seedPosts();

console.log("Database seeded successfully!"); }

async function clearDatabase() { // Delete in reverse order of dependencies await db.delete(posts); await db.delete(coe); await db.delete(cars); }

Seed with Faker.js

pnpm -F @sgcarstrends/database add -D @faker-js/faker

import { faker } from "@faker-js/faker";

export async function seedRealisticCars(count = 100) { const makes = ["Toyota", "Honda", "BMW", "Mercedes"]; const carData = Array.from({ length: count }, () => ({ id: nanoid(), make: faker.helpers.arrayElement(makes), model: faker.vehicle.model(), month: faker.date.between({ from: "2020-01-01", to: "2024-12-31" }).toISOString().slice(0, 7), number: faker.number.int({ min: 10, max: 500 }), }));

// Batch insert for performance const batchSize = 50; for (let i = 0; i < carData.length; i += batchSize) { await db.insert(cars).values(carData.slice(i, i + batchSize)); } }

Environment-Specific Seeds

export async function seed() { const env = process.env.NODE_ENV || "development";

switch (env) { case "development": await seedDevelopment(); // Small, predictable dataset break; case "test": await seedTesting(); // Minimal, deterministic data break; case "staging": await seedStaging(); // Larger, production-like dataset break; } }

Idempotent Seeds (Upsert)

await db.insert(cars).values(carData).onConflictDoUpdate({ target: cars.id, set: { make: carData[0].make, number: carData[0].number, updatedAt: new Date() }, });

Check Before Insert

export async function seedIfEmpty() { const existing = await db.select().from(cars).limit(1); if (existing.length > 0) { console.log("Database has data, skipping seed"); return; } await seedCars(); }

Transactions

await db.transaction(async (tx) => { await tx.insert(cars).values([...carData]); await tx.insert(coe).values([...coeData]); });

CLI for Selective Seeding

// packages/database/scripts/seed-cli.ts const seeders = { cars: seedCars, coe: seedCOE, posts: seedPosts, all: seedAll }; const target = process.argv[2] as keyof typeof seeders;

if (!target || !seeders[target]) { console.error("Usage: pnpm db:seed [cars|coe|posts|all]"); process.exit(1); }

seederstarget.then(() => process.exit(0)).catch(() => process.exit(1));

Best Practices

• Idempotent: Safe to run multiple times (use upserts or check-before-insert)

• Environment-Specific: Different data for dev/test/staging

• Batch Inserts: Use batching for large datasets

• Relationships: Seed parent tables first

• Transactions: Use for atomic seeding

• Logging: Provide clear progress feedback

References

• packages/database/CLAUDE.md for schema details

• See schema-design skill for migrations