How to recover an idUsuario(user_id) from an idAnuncio(ad_id) models by Discount(Discount) Discounts? REST API

Question

I need to do a query to recover a User’s discounts(idUsuario = user_id) by the Discount models' numbers, however, discount is only related to an idAnuncio(ad_id), so it’s like recovering an id via another id...

The API architecture follows the MVR standard and models and Routes are in the Express structure.

Database is the sqlite.

Follows the model structure:

Follow the get of a Discount, which I need to do by idUsuario(user_id):

module.exports = app => {

const Discount = app.db.models.Discount;

//rota para todos descontos somente de um usuario/fornecedor 
app.route("/discounts/provider/:ad_id")
    .get((req, res) => {
        Discount.findAll({ where: req.params })
            .then(result => {
                if (result) {
                    res.json(result);
                } else {
                    res.sendStatus(404);
                }
            })
            .catch(error => {
                res.status(412).json({ msg: error.message });
            });
    })
}

Follow the db.js database file:

const fs = require('fs');
const path = require('path');
const Sequelize = require('sequelize');
let db = null;

module.exports = app => {
if (!db) {
    const config = app.libs.config;
    const sequelize = new Sequelize(
        config.database,
        config.username,
        config.password,
        config.params
    );
    db = {
        sequelize,
        Sequelize,
        models: {}
    };
    const dir = path.join(__dirname, "models");
    fs.readdirSync(dir).forEach(file => {
        const modelDir = path.join(dir, file);
        const model = sequelize.import(modelDir);
        db.models[model.name] = model;
    });
    Object.keys(db.models).forEach(key => {
        db.models[key].associate(db.models);
    });
}
    return db;
};