dbObjects.js

const Sequelize = require("sequelize");

const sequelize = new Sequelize("database", "username", "password", {
	host: "localhost",
	dialect: "sqlite",
	logging: false,
	storage: "database.sqlite",
});

const Users = require("./models/Users.js")(sequelize, Sequelize.DataTypes);
const CurrencyShop = require("./models/CurrencyShop.js")(sequelize, Sequelize.DataTypes);
const UserItems = require("./models/UserItems.js")(sequelize, Sequelize.DataTypes);

UserItems.belongsTo(CurrencyShop, { foreignKey: "item_id", as: "item" });

Reflect.defineProperty(Users.prototype, "addItem", {
	value: async function addItem(item) {
		const userItem = await UserItems.findOne({
			where: { user_id: this.user_id, item_id: item.id },
		});

		if (userItem) {
			userItem.amount += 1;
			return userItem.save();
		}

		return UserItems.create({ user_id: this.user_id, item_id: item.id, amount: 1 });
	},
});

Reflect.defineProperty(Users.prototype, "getItems", {
	value: function getItems() {
		return UserItems.findAll({
			where: { user_id: this.user_id },
			include: ["item"]
		});
	},
});

module.exports = { Users, CurrencyShop, UserItems };