sequelize "findbyid" is not a function but apparently "findAll" is

I am getting a very strange problem with sequelize, When I try to call the function findAll it works fine (same for create and destroy), but when I try to call function "findById", it throws "findById is not a function" (same for "FindOne").

//works fine
var gammes = models.gamme.findAll().then(function(gammes) {
        res.render('admin/gammes/gestion_gamme',{
            layout: 'admin/layouts/structure' ,
            gammes : gammes,
            js: "gammes"
        });
    });

// throws models.gamme.findById is not a function
models.gamme.findById(req.params.id).then(function(gamme) {
        gamme.update({
            nom: req.body.nom
        }).then(function () {
            res.redirect("/gammes");
        })
    });

Gamme.js model

module.exports = function (sequelize, DataTypes) {
    "use strict";
    var gamme = sequelize.define('gamme', {
        id_gamme: {
            type: DataTypes.INTEGER.UNSIGNED,
            autoIncrement: true,
            primaryKey: true
        },
        nom: {
            type: DataTypes.STRING,
            allowNull: false
        }
    }, {
        classMethods: {},
        timestamps: false
    });
    return gamme;
};

With Sequelize v5, findById() was replaced by findByPk(). Replace findById using findByPk and everything should work fine. You can find query doc here

the team of sequelize was deleting this function and replced it by a new function is

> findByPk

like this

// search for known ids
Project.findByPk(123).then(project => {
  // project will be an instance of Project and stores the content of the table entry
  // with id 123. if such an entry is not defined you will get null
})

Directly pass value.

Question.findByPk(question_id).then(question => {
            return res.status(200).json({
                question: question
           });
}).catch(err => {
     console.log(err);
});