## Impacted versions:
 8.0 / 9.0 / 10.0
## Steps to reproduce:
* see https://github.com/odoo/odoo/issues/11841
* in a shell
  1. create an in memory record `order = self.env['purcahse.order'].new({....})`
  2. create an in memory record with a reference to the first one `order_line = self.env['purchase.order.line'].new({'order_id': order, ....})`
  3. order_line.order_id is an in memory recordset
  4. create a record for a model that inherits from mail.thread `self.env['product.product'].create({....})`
  5. At this stage order_line.order_id is an empty recordset

## Current behavior:
 In memory records are dropped when a call is done to self.invalidate_cache
## Expected behavior:
In memory records are preserved when a call is done to self.invalidate_cache


There are lot of places where the method `invalidate_cache` is called and the silent removal of the in memory records from all environments has unpredictable effects on fields modified by a computed method or an onchange or even related fields .... Moreover since all caches are invalidated each time you create / write / unlink  (https://github.com/odoo/odoo/blob/10.0/addons/mail/models/mail_followers.py#L111) an instance of a model that inherits from 'mail.thread', the performances of the server are severely penalized.

OPW703903

"""Prepare the dict of values to create the new invoice for a
           purchase order. This method may be overridden to implement custom
           invoice generation (making sure to call super() to establish
           a clean extension chain).
           :param browse_record order: purchase.order record to invoice
           :param list(int) line_ids: list of invoice line IDs that must be
                                      attached to the invoice
           :return: dict of value to create() the invoice
        """
        journal_ids = self.pool['account.journal'].search(
                            cr, uid, [('type', '=', 'purchase'),
                                      ('company_id', '=', order.company_id.id)],
                            limit=1)
        if not journal_ids:
            raise osv.except_osv(
                _('Error!'),
                _('Define purchase journal for this company: "%s" (id:%d).') % \
                    (order.company_id.name, order.company_id.id))
        return {
            'name': order.partner_ref or order.name,
            'reference': order.partner_ref or order.name,