diff --git a/modules/purchase/purchase.py b/modules/purchase/purchase.py
index 480da93d6d..2ee31b2a7a 100644
--- a/modules/purchase/purchase.py
+++ b/modules/purchase/purchase.py
@@ -2334,7 +2334,7 @@ class ModifyHeader(Wizard):
         Line = pool.get('purchase.line')
 
         purchase = self.get_purchase()
-        values = self.start._save_values
+        values = self.start._save_values()
         self.model.write([purchase], values)
         self.model.log([purchase], 'write', ','.join(sorted(values.keys())))
 
diff --git a/modules/quality/quality.py b/modules/quality/quality.py
index c0b3d10153..bc626b1454 100644
--- a/modules/quality/quality.py
+++ b/modules/quality/quality.py
@@ -830,7 +830,7 @@ class Inspect(Wizard):
         pool = Pool()
         Inspection = pool.get('quality.inspection')
         inspection = self.store.inspections[0]
-        Inspection.write([inspection], self.inspection._save_values)
+        Inspection.write([inspection], self.inspection._save_values())
         inspection.process()
         return 'next_'
 
diff --git a/modules/sale/sale.py b/modules/sale/sale.py
index 2b2299fcc7..130a1cef22 100644
--- a/modules/sale/sale.py
+++ b/modules/sale/sale.py
@@ -2411,7 +2411,7 @@ class ModifyHeader(Wizard):
         Line = pool.get('sale.line')
 
         sale = self.get_sale()
-        values = self.start._save_values
+        values = self.start._save_values()
         self.model.write([sale], values)
         self.model.log([sale], 'write', ','.join(sorted(values.keys())))
 
diff --git a/modules/web_shop_shopify/web.py b/modules/web_shop_shopify/web.py
index be83be7638..b8fc1ce1aa 100644
--- a/modules/web_shop_shopify/web.py
+++ b/modules/web_shop_shopify/web.py
@@ -566,7 +566,7 @@ class Shop(metaclass=PoolMeta):
             shop = sale.web_shop
             with shop.shopify_session():
                 sale = Sale.get_from_shopify(shop, order, sale=sale)
-                if sale._changed_values:
+                if sale._changed_values():
                     sale.untaxed_amount_cache = None
                     sale.tax_amount_cache = None
                     sale.total_amount_cache = None
diff --git a/trytond/CHANGELOG b/trytond/CHANGELOG
index f62611a247..d718ade873 100644
--- a/trytond/CHANGELOG
+++ b/trytond/CHANGELOG
@@ -1,3 +1,4 @@
+* Change _changed_values and _save_values properties to method
 * Add configuration for report convert command
 * Use process pool to run cron
 * Lock only running cron record
diff --git a/trytond/doc/ref/models.rst b/trytond/doc/ref/models.rst
index 3551c5733a..1859fd2173 100644
--- a/trytond/doc/ref/models.rst
+++ b/trytond/doc/ref/models.rst
@@ -216,6 +216,31 @@ Class methods:
 
 Instance methods:
 
+.. method:: ModelView._changed_values()
+
+   Return the values changed since the instantiation.
+   By default, the value of a field is its internal representation except:
+
+      - for :class:`~trytond.model.fields.Many2One` and
+        :class:`~trytond.model.fields.One2One` field: the
+        :attr:`~trytond.model.Model.id`.
+
+      - for :class:`~trytond.model.fields.Reference` field: the string '<model
+        name>,<record id>'.
+
+      - for :class:`~trytond.model.fields.One2Many` and
+        :class:`~trytond.model.fields.Many2Many`: a dictionary composed of
+        three keys:
+
+         - ``add``: a list of tuple, the first element is the index where the
+           new line is added, the second element is default values.
+
+         - ``update``: a list of dictionary of changed values including the
+           ``id``.
+
+         - ``remove``: a list of ids.
+
+
 .. method:: ModelView.on_change(fieldnames)
 
    Return the list of changes by calling ``on_change`` method of each field.
@@ -523,6 +548,11 @@ Dual methods:
 
 Instance methods:
 
+.. method:: ModelStorage._save_values()
+
+   Returns the modified values from the saved one, which can be used with
+   :meth:`~ModelStorage.create` or :meth:`~ModelStorage.write`.
+
 .. method:: ModelStorage.resources()
 
    Return a dictionary with the number of attachments (``attachment_count``),
diff --git a/trytond/trytond/model/fields/field.py b/trytond/trytond/model/fields/field.py
index ed1b338758..9f6d2a6249 100644
--- a/trytond/trytond/model/fields/field.py
+++ b/trytond/trytond/model/fields/field.py
@@ -192,7 +192,7 @@ def instantiate_context(field, record):
 
 
 def on_change_result(record):
-    return record._changed_values
+    return record._changed_values()
 
 
 def on_change_with_result(fieldname):
@@ -201,7 +201,7 @@ def on_change_with_result(fieldname):
         def wrapper(self, *args, **kwargs):
             value = func(self, *args, **kwargs)
             setattr(self, fieldname, value)
-            return self._changed_values
+            return self._changed_values()
         return wrapper
     return decorator
 
diff --git a/trytond/trytond/model/modelstorage.py b/trytond/trytond/model/modelstorage.py
index 606f3cbed8..4b41d7e33c 100644
--- a/trytond/trytond/model/modelstorage.py
+++ b/trytond/trytond/model/modelstorage.py
@@ -1881,7 +1881,6 @@ class ModelStorage(Model):
                     **{k: v for k, v in data.items() if k not in to_delete})
         return value
 
-    @property
     def _save_values(self):
         values = {}
         if not self._values:
@@ -1923,13 +1922,13 @@ class ModelStorage(Model):
                         t_values = None
                     try:
                         if target.id is None or target.id < 0:
-                            to_create.append(target._save_values)
+                            to_create.append(target._save_values())
                         else:
                             if target.id in previous:
                                 previous.remove(target.id)
                             else:
                                 to_add.append(target.id)
-                            target_values = target._save_values
+                            target_values = target._save_values()
                             if target_values:
                                 to_write.append(
                                     ('write', [target.id], target_values))
@@ -1987,7 +1986,7 @@ class ModelStorage(Model):
                     continue
                 while True:
                     try:
-                        save_values[record] = record._save_values
+                        save_values[record] = record._save_values()
                         break
                     except _UnsavedRecordError as e:
                         warnings.warn(
diff --git a/trytond/trytond/model/modelview.py b/trytond/trytond/model/modelview.py
index e0d33d1007..8d223b5301 100644
--- a/trytond/trytond/model/modelview.py
+++ b/trytond/trytond/model/modelview.py
@@ -840,20 +840,7 @@ class ModelView(Model):
                 for r in result]
         return result
 
-    @property
     def _changed_values(self):
-        """Return the values changed since the instantiation.
-        By default, the value of a field is its internal representation except:
-            - for Many2One and One2One field: the id.
-            - for Reference field: the string model,id
-            - for One2Many and Many2Many: a dictionary composed of three keys:
-                - add: a list of tuple, the first element is the index where
-                  the new line is added, the second element is
-                  `_default_values`
-                - update: a list of dictionary of `_changed_values` including
-                  the `id`
-                - remove: a list of ids
-        """
         from .modelstorage import ModelStorage
         changed = {}
         init_values = self._init_values or self._record()
@@ -905,7 +892,7 @@ class ModelView(Model):
                         if target.id in previous:
                             previous.remove(target.id)
                             if isinstance(target, ModelView):
-                                target_changed = target._changed_values
+                                target_changed = target._changed_values()
                                 if target_changed:
                                     target_changed['id'] = target.id
                                     value['update'].append(target_changed)
@@ -916,7 +903,7 @@ class ModelView(Model):
                                 target_init_values = target._init_values
                                 target._init_values = None
                                 try:
-                                    added_values = target._changed_values
+                                    added_values = target._changed_values()
                                 finally:
                                     target._init_values = target_init_values
                             else:
diff --git a/trytond/trytond/tests/test_modelstorage.py b/trytond/trytond/tests/test_modelstorage.py
index 755cdbe9a8..7d515346ed 100644
--- a/trytond/trytond/tests/test_modelstorage.py
+++ b/trytond/trytond/tests/test_modelstorage.py
@@ -164,7 +164,7 @@ class ModelStorageTestCase(TestCase):
         record.target = target = Target()
 
         with self.assertRaises(_UnsavedRecordError) as cm:
-            record._save_values
+            record._save_values()
 
         self.assertEqual(cm.exception.record, target)
 
diff --git a/trytond/trytond/tests/test_modelview.py b/trytond/trytond/tests/test_modelview.py
index 2ac3459994..d6b45b11c4 100644
--- a/trytond/trytond/tests/test_modelview.py
+++ b/trytond/trytond/tests/test_modelview.py
@@ -187,7 +187,7 @@ class ModelView(TestCase):
 
         record = Model(targets=[], m2m_targets=[], m2m_function=[])
 
-        self.assertEqual(record._changed_values, {})
+        self.assertEqual(record._changed_values(), {})
 
         record.name = 'foo'
         record.target = Target(1)
@@ -195,7 +195,7 @@ class ModelView(TestCase):
         record.targets = [Target(name='bar')]
         record.multiselection = ['a']
         record.dictionary = {'key': 'value'}
-        self.assertEqual(record._changed_values, {
+        self.assertEqual(record._changed_values(), {
                 'name': 'foo',
                 'target': 1,
                 'ref_target': 'test.modelview.changed_values.target,2',
@@ -217,7 +217,7 @@ class ModelView(TestCase):
             dictionary={'key': 'value'},
             )
 
-        self.assertEqual(record._changed_values, {})
+        self.assertEqual(record._changed_values(), {})
 
         target = record.targets[0]
         target.name = 'bar'
@@ -229,7 +229,7 @@ class ModelView(TestCase):
         dico = record.dictionary.copy()
         dico['key'] = 'another value'
         record.dictionary = dico
-        self.assertEqual(record._changed_values, {
+        self.assertEqual(record._changed_values(), {
                 'targets': {
                     'update': [{'id': 1, 'name': 'bar'}],
                     'delete': [2],
@@ -244,12 +244,12 @@ class ModelView(TestCase):
 
         # change only one2many record
         record = Model(targets=[{'id': 1, 'name': 'foo'}])
-        self.assertEqual(record._changed_values, {})
+        self.assertEqual(record._changed_values(), {})
 
         target, = record.targets
         target.name = 'bar'
         record.targets = record.targets
-        self.assertEqual(record._changed_values, {
+        self.assertEqual(record._changed_values(), {
                 'targets': {
                     'update': [{'id': 1, 'name': 'bar'}],
                     },
@@ -261,7 +261,7 @@ class ModelView(TestCase):
         target = Target(id=1)
         record._values['targets'] = [target]
         target.name = 'foo'
-        self.assertEqual(record._changed_values, {
+        self.assertEqual(record._changed_values(), {
                 'targets': {
                     'add': [(0, {'id': 1, 'name': 'foo'})],
                     },
@@ -279,7 +279,7 @@ class ModelView(TestCase):
             record = Model()
             record.m2m_function = record.on_change_with_m2m_function()
 
-            self.assertEqual(record._changed_values, {
+            self.assertEqual(record._changed_values(), {
                     'm2m_function': {'add': [(0, {'id': 42})]},
                     })
 
@@ -299,7 +299,7 @@ class ModelView(TestCase):
         target1.name = "test"
         record.targets = [target1, Target(name="baz")]
 
-        self.assertEqual(record._changed_values, {
+        self.assertEqual(record._changed_values(), {
                 'targets': {
                     'delete': [target2.id],
                     'update': [{'id': target1.id, 'name': "test"}],
@@ -318,7 +318,7 @@ class ModelView(TestCase):
         record = Model(targets=[target])
         Model.targets.remove(record, [target])
 
-        self.assertEqual(record._changed_values, {
+        self.assertEqual(record._changed_values(), {
                 'targets': {
                     'remove': [1],
                     },
@@ -335,7 +335,7 @@ class ModelView(TestCase):
         record = Model(m2m_targets=[target])
         Model.m2m_targets.delete(record, [target])
 
-        self.assertEqual(record._changed_values, {
+        self.assertEqual(record._changed_values(), {
                 'm2m_targets': {
                     'delete': [1],
                     },
@@ -352,7 +352,7 @@ class ModelView(TestCase):
         record = Model()
         record.stored_target = target
 
-        self.assertEqual(record._changed_values, {
+        self.assertEqual(record._changed_values(), {
                 'stored_target': target.id,
                 'stored_target.': {
                     'rec_name': "Target",
@@ -372,7 +372,7 @@ class ModelView(TestCase):
         target.name = "Target"
         record.targets = [target]
 
-        self.assertEqual(record._changed_values, {
+        self.assertEqual(record._changed_values(), {
                 'name': "Record",
                 'targets': {
                     'add': [(0, {'id': None, 'name': "Target"})],