Need advice on how to populate "through" table in Sequelize?

Question

I'm trying to figure out how N:M works in sequelize, and I have a problem with populating the "through" table.

So I have these models :

Product / Category models

'use strict';
module.exports = (sequelize, DataTypes) => {
  const Category = sequelize.define('Category', {
    name: DataTypes.STRING
  }, {});

  return Category;
};


module.exports = (sequelize, DataTypes) => {
  const Product = sequelize.define(
    'Product',
    {
      name: DataTypes.STRING,
      price: DataTypes.INTEGER,
      description: DataTypes.TEXT,
      inStock: DataTypes.BOOLEAN
    },
    {}
  )
  Product.associate = function(models) {
    // associations can be defined here
    models.Product.belongsToMany(models.Category, {
      through: 'Product_categories'
    })
    models.Category.belongsToMany(models.Product, {
      through: 'Product_categories'
    })
  }
  return Product
}

This creates the "Product_categories" table in my database with a categoryId and the productId. Let's say I have a game as a product, which belongs in multiple categories ( lets say ps4 and xbox ).

How do I actually populate the "Product_categories" table and associate the product (game) to categories with Id 1 and 2 ( playstation and xbox ).

I'm still figuring out Sequelize and ORM in general, so this is where I got a little stuck. Am I supposed to add something in the actual model ? Or do I handle it in the route upon product creation ? I'm so confused ><

I read all the documentation, but to be honest I just got a little confused, so I was hoping someone can explain this to me.

Also, this is the route I use to create the said product :

router.post('/product', async (req, res, next) => {
  try {
    const { name, price, description, inStock } = req.body

    const createdProduct = await Product.create({
      name,
      price,
      description,
      inStock
    })

    res.send(createdProduct)
  } catch (error) {
    next(error)
  }
})

Help much appreciated ! Thanks !!

Answer 1

You can try:

await createdProduct.addCategory(category)

or

await createdProduct.addCategorys(categories)

see Many-to-many associations