db.js

import Sequelize from 'sequelize';
import fs from 'fs';
import path from 'path';

let db = null;

module.exports = (app) => {
  if (db !== null) return db;
  const config = app.config;

  const sequelize = new Sequelize(
    config.database,
    config.username,
    config.password,
    config.params
  );

  db = {
    sequelize,
    Sequelize,
    models: {},
  };

  const dir = path.join(__dirname, 'models');

  fs.readdirSync(dir).forEach(file => {
    const modelDir = path.join(dir, file);
    const model = sequelize.import(modelDir);

    if (model) {
      db.models[model.name] = model;
    }
  });

  Object.keys(db.models).forEach(key => {
    db.models[key].associate(db.models);
  });

  return db;
};