Added migrate property. Refactor

party.py

@@ -3,8 +3,11 @@
 from trytond.model import ModelSQL, fields
 from trytond.pool import PoolMeta, Pool
 from trytond.modules.company.model import CompanyValueMixin
+from trytond import backend
+from trytond.tools.multivalue import migrate_property
 
 __all__ = ['Party', 'PartyParty']
+parties_names = ['customer_to_invoice', 'supplier_to_invoice']
 
 
 class Party:
@@ -19,7 +22,7 @@ class Party:
     @classmethod
     def multivalue_model(cls, field):
         pool = Pool()
-        if field in {'customer_to_invoice', 'supplier_to_invoice'}:
+        if field in parties_names:
             return pool.get('party.party.party')
         return super(Party, cls).multivalue_model(field)
 
@@ -29,3 +32,21 @@ class PartyParty(ModelSQL, CompanyValueMixin):
     __name__ = 'party.party.party'
     customer_to_invoice = fields.Many2One('party.party', 'Customer to invoice')
     supplier_to_invoice = fields.Many2One('party.party', 'Supplier to invoice')
+
+    @classmethod
+    def __register__(cls, module_name):
+        TableHandler = backend.get('TableHandler')
+        exist = TableHandler.table_exist(cls._table)
+
+        super(PartyParty, cls).__register__(module_name)
+
+        if not exist:
+            cls._migrate_property([], [], [])
+
+    @classmethod
+    def _migrate_property(cls, field_names, value_names, fields):
+        field_names.extend(parties_names)
+        value_names.extend(parties_names)
+        fields.append('company')
+        migrate_property('party.party',
+            field_names, cls, value_names, fields=fields)