Ember.js : Modify request URL

I create an Ember app with a Symfony REST api. I also use the REST adapter for my requests.

I have 2 models in my app : users and their related comments. I already created CRUD operations for my user properties and now I focus on the CRUD operations for comments.

Model user.js

export default DS.Model.extend({
    firstName: DS.attr('string'),
    lastName: DS.attr('string'),

    comments: DS.hasMany('comment')
});

Model comment.js

export default DS.Model.extend({
    title: DS.attr('string'),
    message: DS.attr('string'),

    contact: DS.belongsTo('contact')
});

I have a route which shows all comments (and other data) of a given user. The request loads the user object and his relations. On the view I also have a form and an action to create a new comment for this user.

Route users/get/comments.js

import Ember from 'ember';

export default Ember.Route.extend({
    model(params) {
        return this.modelFor('user.get', params.user_id);
    },
});

Controller users/get/comments.js

import Ember from 'ember';

export default Ember.Controller.extend({

    newComment: null,
    user: null,

    init: function() {
        this._super(...arguments);

        let comment = this.store.createRecord('contact');
        this.set('newComment', comment);
    },

    actions: {
        saveComment: function() {
            let user = this.get('model');
            let comment = this.get('newComment');

            comment.set('user', user);
            comment.save();
        }
    }
});

Everything works, except for the request sent to the backend. I loaded the comments from the user, so I expect a call to :

POST http://ift.tt/2hAqPgU

Instead the call is sent to :

POST http://ift.tt/2fPXc7h

Do you know why and how could I correct it ?

Second problem, the model is loaded from the 'user.get' route. This works because the user comes from this route to this page, but... It's doesn't work if the user enters directly the URL for comments. That sound logical, but I have no clue how to correct this problem... Can you help me ?