## 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

if not ids: return {}
        res = {}
        for id in ids:
            res[id] = [0.0,0.0]
        cr.execute('''SELECT
                p.order_id, sum(m.product_qty), m.state
            FROM
                stock_move m
            LEFT JOIN
                purchase_order_line p on (p.id=m.purchase_line_id)
            WHERE
                p.order_id IN %s GROUP BY m.state, p.order_id''',(tuple(ids),))
        for oid,nbr,state in cr.fetchall():
            if state=='cancel':
                continue
            if state=='done':
                res[oid][0] += nbr or 0.0
                res[oid][1] += nbr or 0.0
            else:
                res[oid][1] += nbr or 0.0
        for r in res:
            if not res[r][1]:
                res[r] = 0.0
            else:
                res[r] = 100.0 * res[r][0] / res[r][1]
        return res
    def _get_order(self, cr, uid, ids, context=None):