Fixing Association Issues in Sequelize: A Step-by-Step Guide

Why Your Sequelize Association Doesn’t Work?

Sequelize is a popular ORM (Object-Relational Mapping) library used for interacting with databases in Node.js. It provides a high-level, promise-based API for defining database models and performing operations on them.

In this article, we’ll explore the issue of why an association between two Sequelize models doesn’t work as expected. We’ll dive into the configuration, model definitions, and migration scripts to identify the problem and provide a solution.

Understanding the Basics

Before we begin, let’s review some fundamental concepts in Sequelize:

Models: These represent database tables and are used to define their schema.
Associations: Define relationships between models.
Migrations: Used to create and modify database schema.

Configuring Your Database

Your database configuration is defined in the config/database.js file:

import 'dotenv/config'
import { Options } from 'sequelize'

const config: Options = {
  username: process.env.DB_USER ?? 'root',
  password: process.env.DB_PASS ?? '123456',
  database: 'gastos_app_db',
  host: process.env.DB_HOST ?? 'localhost',
  port: Number(process.env.DB_PORT) ?? 3002,
  dialect: 'mysql',
  dialectOptions: {
    timezone: 'Z'
  },
  logging: false
}

module.exports = config

Your model definitions are also defined in separate files for each model. For example, User.js and Gasto.js.

Defining the User Model

The User model is defined as follows:

import { DataTypes } from 'sequelize'
import db from '.'
import { Gasto } from './Gasto'

export const User = db.define('User', {
  id: {
    type: DataTypes.INTEGER,
    autoIncrement: true,
    allowNull: false,
    primaryKey: true
  },
  username: {
    type: DataTypes.STRING,
    allowNull: false
  },
  email: {
    type: DataTypes.STRING,
    allowNull: false
  },
  password: {
    type: DataTypes.STRING,
    allowNull: false
  },
  role: {
    type: DataTypes.STRING,
    allowNull: false
  }
}, {
  timestamps: false,
  tableName: 'users',
  underscored: true
})

User.hasMany(Gasto, {
  foreignKey: 'userId',
  onDelete: 'CASCADE'
})

Gasto.hasOne(User, {
  foreignKey: 'id'
})

The User model defines an association with the Gasto model using the hasMany method.

Defining the Gasto Model

Similarly, the Gasto model is defined as follows:

import { DataTypes } from 'sequelize'
import db from '.'
import { User } from './User'

export const Gasto = db.define('Gasto', {
  id: {
    type: DataTypes.INTEGER,
    primaryKey: true,
    autoIncrement: true
  },
  userId: {
    type: DataTypes.INTEGER,
    allowNull: false
  },
  type: {
    type: DataTypes.STRING,
    allowNull: false
  },
  value: {
    type: DataTypes.STRING,
    allowNull: false
  },
  gastoDate: {
    type: DataTypes.STRING,
    allowNull: false
  }
}, {
  timestamps: false,
  tableName: 'gastos',
  underscored: true
})

The Gasto model defines an association with the User model using the hasOne method.

Defining the Gasto Migration

Your migration script for creating the gastos table is defined as follows:

'use strict'

/** @type {import('sequelize-cli').Migration} */
module.exports = {
  async up (queryInterface, Sequelize) {
    await queryInterface.createTable('gastos', {
      id: {
        type: Sequelize.INTEGER,
        primaryKey: true,
        allowNull: false,
        autoIncrement: true
      },
      user_id: {
        type: Sequelize.INTEGER,
        allowNull: false
      },
      type: {
        type: Sequelize.STRING,
        allowNull: false
      },
      value: {
        type: Sequelize.STRING,
        allowNull: false
      },
      gasto_date: {
        type: Sequelize.STRING,
        allowNull: false
      }
    })
  },

  async down (queryInterface, Sequelize) {
    await queryInterface.dropTable('gastos')
  }
}

However, the user_id field in this migration does not have a foreign key definition or on update/on delete logic. This is the problem.

The Solution

To fix the issue, you need to add a foreign key definition and on update/on delete logic to the user_id field in your migration script:

'use strict'

/** @type {import('sequelize-cli').Migration} */
module.exports = {
  async up (queryInterface, Sequelize) {
    await queryInterface.createTable('gastos', {
      id: {
        type: Sequelize.INTEGER,
        primaryKey: true,
        allowNull: false,
        autoIncrement: true
      },
      user_id: {
        type: Sequelize.INTEGER,
        allowNull: false,
        references: {
          model: 'users',
          key: 'id'
        },
        onUpdate: 'CASCADE',
        onDelete: 'CASCADE'
      },
      type: {
        type: Sequelize.STRING,
        allowNull: false
      },
      value: {
        type: Sequelize.STRING,
        allowNull: false
      },
      gasto_date: {
        type: Sequelize.STRING,
        allowNull: false
      }
    })
  },

  async down (queryInterface, Sequelize) {
    await queryInterface.dropTable('gastos')
  }
}

By adding the foreign key definition and on update/on delete logic to the user_id field, you ensure that the relationship between the Gasto model and the User model is properly defined.

Conclusion

In this article, we explored the issue of why an association between two Sequelize models doesn’t work as expected. We reviewed the configuration, model definitions, and migration scripts to identify the problem and provided a solution. By adding foreign key definitions and on update/on delete logic to the relevant fields in your migration script, you can ensure that relationships between models are properly defined.

Note: Make sure to adjust the code according to your specific use case and requirements. This is just an example of how to fix the issue mentioned in the prompt.

Last modified on 2023-07-28