how to remove relation for specific instances with sequelize / mysql

Question

I created a many-to-many association between courses and users like this:

Course.belongsToMany(User, { through: 'CourseUser'});
User.belongsToMany(Course, { through: 'CourseUser'});

which generates a join table called CourseUser.

I add a relation for a specific course and user with the following server side function that happens on the click of a button: the userCourse variable looks like this: { UserId: 7, CourseId: 13 }

  addUser: function(req, res) {
    var userCourse = req.body;
    db.CourseUser.create(userCourse).then(function () {
      res.sendStatus(200);
    });
  }

1. Is this the correct way of adding the association between an existing user and an existing course? (if not, what is the correct way)

2. I would like to have an ability of removing the association when clicking on another button. But I can't quite figure out how to set up the function.

Solution 1

1. If you already have a User and Course instance and are just associating them in addUser, then yes, this is the correct way of creating an association between them.
2. You should be able to remove this association in at least 4 ways:

1: Through User model:

User.removeCourse(courseObject);

2: Through Course model:

Course.removeUser(userObject);

3: On the CourseUser model, without having a CourseUser instance available:

db.CourseUser.destroy({
    where: {...}
});

4: Having a CourseUser instance available:

courseUser.destroy();

You can bind .then and .catch on all these operations to do something on success / on error.

Solution 2

Your model relationship is okay:

Course.belongsToMany(User, { through: 'CourseUser'}); User.belongsToMany(Course, { through: 'CourseUser'});

and values:
{ UserId: 7, CourseId: 13 }

Implementation could look thus for adding a UserCourse relationship:

addUser: function(req, res) {
    const { UserId, CourseId } = req.body;
    db.Course.findOne({
        where: { id: CourseId }
    }).then(course => {
        course.setUsers([UserId])
        res.sendStatus(200);
    }).catch(e => console.log(e));
}

removeUser: function (req, res) {
    const { UserId, CourseId } = req.body;
    db.Course.findOne({
        where: { id: CourseId }
    }).then(course => {
        course.removeUsers([UserId])
        res.sendStatus(200);
    }).catch(e => console.log(e));
}