## 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

"""Return the datetime value to use as Order Date (``date_order``) for the
           Purchase Order created to satisfy the given procurement.
           :param browse_record procurement: the procurement for which a PO will be created.
           :param browse_report company: the company to which the new PO will belong to.
           :param datetime schedule_date: desired Scheduled Date for the Purchase Order lines.
           :rtype: datetime
           :return: the desired Order Date for the PO
        """
        seller_delay = int(procurement.product_id.seller_delay)
        return schedule_date - relativedelta(days=seller_delay)
    def _get_product_supplier(self, cr, uid, procurement, context=None):
        ''' returns the main supplier of the procurement's product given as argument'''
        supplierinfo = self.pool['product.supplierinfo']
        company_supplier = supplierinfo.search(cr, uid,
            [('product_tmpl_id', '=', procurement.product_id.product_tmpl_id.id), ('company_id', '=', procurement.company_id.id)], limit=1, context=context)
        if company_supplier:
            return supplierinfo.browse(cr, uid, company_supplier[0], context=context).name
        return procurement.product_id.seller_id
    def _get_po_line_values_from_proc(self, cr, uid, procurement, partner, company, schedule_date, context=None):
        if context is None:
            context = {}
        uom_obj = self.pool.get('product.uom')
        pricelist_obj = self.pool.get('product.pricelist')
        prod_obj = self.pool.get('product.product')
        acc_pos_obj = self.pool.get('account.fiscal.position')
        po_obj = self.pool.get('purchase.order')
        seller_qty = procurement.product_id.seller_qty if procurement.location_id.usage != 'customer' else 0.0
        pricelist_id = partner.property_product_pricelist_purchase.id