Reset MPTT fields when copying records

The left/right fields must be reset to their default values to allow to compute
the correct new values. As it is common to forget this requirement when
implementing, it is safer to enforce this behaviour directly in the
ModelStorage.copy method.

issue5049
review16741002

trytond/model/modelstorage.py

@@ -297,9 +297,18 @@ class ModelStorage(Model):
                 del data['id']
             return data
 
+        # Reset MPTT field to the default value
+        mptt = set()
+        for field in cls._fields.itervalues():
+            if (isinstance(field, fields.Many2One)
+                    and field.model_name == cls.__name__
+                    and field.left and field.right):
+                mptt.add(field.left)
+                mptt.add(field.right)
         fields_names = [n for n, f in cls._fields.iteritems()
             if (not isinstance(f, fields.Function)
-                or isinstance(f, fields.Property))]
+                or isinstance(f, fields.Property))
+            and n not in mptt]
         ids = map(int, records)
         datas = cls.read(ids, fields_names=fields_names)
         datas = dict((d['id'], d) for d in datas)