Why Doesn't Sequelize Create My Foreign Key Column in Model Associations?

Sequelize Model Association Not Creating Foreign Key Column

In Sequelize, an association defines the relationship between two or more models. It provides a convenient way to access related data and perform complex queries. However, some users encounter an issue where Sequelize does not create a foreign key column for a particular model. This problem arises despite identical association definitions for other models.

Understanding Foreign Key Creation

Sequelize will automatically create foreign key columns when an association is established between two models. This occurs when the foreignKey property is specified in the association options. For example, in the provided User model, the belongsTo association is defined with a foreignKey of role_id. Normally, this would result in the creation of a role_id column in the User table.

Resolving the Issue

The solution to this issue lies in ensuring that all models are registered and associated in one central location. By centralizing model registration and association, Sequelize can correctly handle dependencies and create the necessary foreign key columns.

Implementing Centralized Model Registration and Association

The following code demonstrates how to register and associate models in a single file:

// database.js

// Register all models in one place
const fs = require('fs');
const path = require('path');
const Sequelize = require('sequelize');
const db = {};

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

// Create a Sequelize instance
const sequelize = new Sequelize(/* your connection settings here */);

// Register models and add them to the db object
fs.
  readdirSync(models).
  filter(function (file) {
    return (file.indexOf('.') !== 0) && (file !== basename) && (file.slice(-3) === '.js');
  }).
  forEach(function (file) {
    // Sequelize version <= 5.x
    var model = sequelize['import'](path.join(models, file));
    // Sequelize version >= 6.x
    // var model = require(path.join(models, file))(
    //   sequelize,
    //   Sequelize.DataTypes
    // );
    db[model.name] = model;
  });

// Associate models within the db object
Object.keys(db).forEach(function (modelName) {
  if (db[modelName].associate) {
    db[modelName].associate(db);
  }
});

db.Sequelize = Sequelize; // for accessing static props and functions like Op.or
db.sequelize = sequelize; // for accessing connection props and functions like 'query' or 'transaction'

module.exports = db;

Usage Example

In other modules of your codebase, you can access the centralized database connection and use the registered models like so:

const db = require('../database');
const { Op } = require('sequelize');

// Use models defined in database.js
const users = await db.user.findAll({
  where: {
    [Op.or]: [
      {
        first_name: 'Smith'
      },
      {
        last_name: 'Smith'
      }
    ]
  }
});

By following these guidelines, you can ensure that all your Sequelize models are correctly associated and that the appropriate foreign key columns are created.

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