## 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

"""Collects require data from purchase order line that is used to create invoice line
        for that purchase order line
        :param account_id: Expense account of the product of PO line if any.
        :param browse_record order_line: Purchase order line browse record
        :return: Value for fields of invoice lines.
        :rtype: dict
        """
        return {
            'name': order_line.name,
            'account_id': account_id,
            'price_unit': order_line.price_unit or 0.0,
            'quantity': order_line.product_qty,
            'product_id': order_line.product_id.id or False,
            'uos_id': order_line.product_uom.id or False,
            'invoice_line_tax_id': [(6, 0, [x.id for x in order_line.taxes_id])],
            'account_analytic_id': order_line.account_analytic_id.id or False,
            'purchase_line_id': order_line.id,
        }
    def _prepare_invoice(self, cr, uid, order, line_ids, context=None):