How to define table associations with sequelize. TypeError: User.hasMany is not a function

Question

I'm working on an E-commerce Express API, and i'm using 'sequelize' module for database manipulation. For now i have only two tables: And my project structure is as follows:

bin
 -www
config
 -database.js
models
 -order.js
 -user.js
routes
 -user.js
.env
app.js
package.json
package-lock.json

database.js file:

    require('dotenv').config();
    const Sequelize = require('sequelize');

    module.exports = new Sequelize(
        process.env.DATABASE_NAME,
        process.env.DATABASE_USERNAME,
        process.env.DATABASE_PASSWORD, {
            port: process.env.DATABASE_PORT,
            host: process.env.DATABASE_HOST,
            dialect: 'mysql',
        }

);

User.hasMany(Order);
Order.belongsTo(User, {constraints: false});

models-user.js

    const db = require('../config/database');
const Sequelize = require("sequelize");

const User = db.define('user', {
    username: {
        type: Sequelize.STRING(32),
        unique: true,
        primaryKey: true,
        allowNull: false
    },
    email: {
        type: Sequelize.STRING(254),
        unique: true,
        allowNull: false,
    },
    password: {
        type: Sequelize.STRING(128),
        allowNull: false,
    },
    /*name: {
        type: Sequelize.STRING
    },
    isAdmin: {
        type: Sequelize.BOOLEAN
    },*/
}, {
    freezeTableName: true,
    timestamps: false,
    underScored: true
    });

modules.exports=User;

models-order.js

 const db = require('../config/database');
const Sequelize = require('sequelize');

const Order = db.define('order', {
        id: {
            type: Sequelize.INTEGER,
            primaryKey: true,
            autoIncrement: true,
            allowNull: false
        },
        dateTime: {
            type: Sequelize.DATE,
            allowNull: false
        },
        totalPrice: {
            type: Sequelize.INTEGER,
            allowNull: false
        }
    }, {
        freezeTableName: true,
        timestamps: false,
        underscored: true
    }
    );

module.exports=Order;

When i start the application, i get

TypeError: User.hasMany is not a function
at Object.<anonymous> (C:\Users\danfe\Documents\GitHub\USocks_Backend\config\database.js:23:6)
at Module._compile (internal/modules/cjs/loader.js:701:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:712:10)
at Module.load (internal/modules/cjs/loader.js:600:32)
at tryModuleLoad (internal/modules/cjs/loader.js:539:12)
at Function.Module._load (internal/modules/cjs/loader.js:531:3)
at Module.require (internal/modules/cjs/loader.js:637:17)
at require (internal/modules/cjs/helpers.js:22:18)
at Object.<anonymous> (C:\Users\danfe\Documents\GitHub\USocks_Backend\models\user.js:1:74)
at Module._compile (internal/modules/cjs/loader.js:701:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:712:10)
at Module.load (internal/modules/cjs/loader.js:600:32)
at tryModuleLoad (internal/modules/cjs/loader.js:539:12)
at Function.Module._load (internal/modules/cjs/loader.js:531:3)
at Module.require (internal/modules/cjs/loader.js:637:17)
at require (internal/modules/cjs/helpers.js:22:18)
at Object.<anonymous> (C:\Users\danfe\Documents\GitHub\USocks_Backend\config\passport.js:6:14)
at Module._compile (internal/modules/cjs/loader.js:701:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:712:10)
at Module.load (internal/modules/cjs/loader.js:600:32)
at tryModuleLoad (internal/modules/cjs/loader.js:539:12)
at Function.Module._load (internal/modules/cjs/loader.js:531:3)

I did some googling, and it might has something to do with circular dependency? But I'm sure, i have quesitons: 1. What's wrong? 2. Am i defining the association correctly? 3. What's the correct way to difine associations?

Answer 1

Your runtime has no idea what is User and Order inside database.js. This is akin to using a variable without defining or initialising it at all. You need to import the User and Order model inside database.js using

const User = require("../models/user.js"); const Order = require("../models/order.js")

You can also define the association inside the models itself. Inside models/order.js and before module.exports do -

Order.associate = function(models) {
Order.belongsTo(models.User,{
  foreignKey:user_id
}) 

But for this to work, you have to property initialise sequelize.

You should use the sequelize-cli to generate your config.json, models, migrations and seeds in the correct way. This way, you just need to import a single db object across your whole project and you will have access to all your models in the correct way.

Answer 2

Yes, it's from circular dependency. When you call "User.hasMany(Order)" User not yet defined.Call "hasMany" and "belongTo" before place when you wanna use this relation