+ 'sale_order_ids': fields.many2many(
+ 'sale.order',
+ 'event_registration_sale_order_rel',
+ 'event_registration_id',
+ 'sale_order_id',
+ 'Related sale order(s)'
+ ),
+ 'invoice_ids': fields.many2many(
+ 'account.invoice',
+ 'event_registration_invoice_id_rel',
+ 'event_registration_id',
+ 'invoice_id',
+ 'Related invoice(s)'
+ ),