## 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 value: return False
        if type(ids)!=type([]):
            ids=[ids]
        pol_obj = self.pool.get('purchase.order.line')
        for po in self.browse(cr, uid, ids, context=context):
            if po.order_line:
                pol_ids = pol_obj.search(cr, uid, [
                    ('order_id', '=', po.id), '|', ('date_planned', '=', po.minimum_planned_date), ('date_planned', '<', value)
                ], context=context)
                pol_obj.write(cr, uid, pol_ids, {'date_planned': value}, context=context)
        self.invalidate_cache(cr, uid, context=context)
        return True
    def _minimum_planned_date(self, cr, uid, ids, field_name, arg, context=None):