Here's the challenge: 

I have added a custom field to the mail.message model.
I want to expose that field in the message thread. I can change the way the thread looks but the value of the new field always comes empty.

I can make the values to be shown by directly editing the /mail/static/src/models/message.js in two places:
1) add...
    if ('read_by' in data) {
        data2.read_by = data.read_by;
    }

    inside convertData(data)

2) Add...
    read_by = attr();

    inside "fields"


Obviously, I can't edit the base code and I need to apply these changes in my own code. How?!


I've tried the following (it's not working):


odoo.define('MY_MODULE.message', function (require) {
    "use strict";

    const { Message } = require('mail.models');
    const Registries = require('mail.Registries');

    const MessageFields = (Message) => class MessageFields extends Message {

        convertData(data) {
            super.convertData(data);
            if ('read_by' in data) {
                data2.read_by = data.read_by;
            }
        }

        fields['read_by'] = attr();
    }
    Registries.Model.extend(Message, MessageFields);
});


Can anyone, please, tell me how to achieve this?