In the very initial days of my work in Node JS if faced this issue. Though Sequelize provide a great ORM for MySQL but the association within the models is a bit tricky. you can find more about associations here
Before getting any further, if you want to get a setup for fully function code setup here it is
For the sake of understanding, lets consider two Models please inside the model directory, models/author.js and models/post.js. Models will look like as follows respectively.
Author Model
'use strict';
const {
Model
} = require('sequelize');
module.exports = (sequelize, DataTypes) => {
class Author extends Model {
/**
* Helper method for defining associations.
* This method is not a part of Sequelize lifecycle.
* The `models/index` file will call this method automatically.
*/
static associate(models) {
// define association here
}
};
Author.init({
slug: DataTypes.STRING,
name: DataTypes.STRING,
}, {
sequelize,
modelName: 'Author',
tableName: 'authors',
});
return Author;
};
Post Model
'use strict';
const {
Model,
} = require('sequelize');
module.exports = (sequelize, DataTypes) => {
class Post extends Model {
/**
* Helper method for defining associations.
* This method is not a part of Sequelize lifecycle.
* The `models/index` file will call this method automatically.
*/
static associate(models) {
this.belongsTo(models.Author, {as: 'Author'});
}
}
Post.init({
slug: DataTypes.STRING,
title: DataTypes.STRING,
excerpt: DataTypes.STRING
}, {
sequelize,
modelName: 'Post',
tableName: 'posts',
});
return Post;
};
As shown in the post model, a belongs too association is made between Post and author. But as the comment suggest, associate method is not a part of Sequelize lifecycle. we have to call it manually.
To achieve that, we need to create *models/index.js with the following content.
index.js
const Sequelize = require("sequelize");
/**
* Database Connection.
**/
const {sequelize, DataTypes} = require('../config/connection')
const Post = require("../models/post")(sequelize, DataTypes);
const Author = require("../models/author")(sequelize, DataTypes);
const models = {
Post,
Author
};
// Run `.associate` if it exists,
// ie create relationships in the ORM
Object.values(models)
.filter(model => typeof model.associate === "function")
.forEach(model => model.associate(models));
const db = {
...models,
sequelize
};
module.exports = db;
Ones you are done with this you can access all you models vie models/index.js
const {Post, Author} = require('../../models');
You can find more about hoe to use association in accessing data here
GitHub Repo for the above code
Below is the link for the video tutorial for the same.
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