diff --git a/tryton/proteus/proteus/__init__.py b/proteus/proteus/__init__.py
index bfad1dc7382cb9fd2c17bef77da699ed36869d3e_cHJvdGV1cy9wcm90ZXVzL19faW5pdF9fLnB5..bf7072adc76db4e62ec3fbde7efde17e7bbd630d_cHJvdGV1cy9wcm90ZXVzL19faW5pdF9fLnB5 100644
--- a/tryton/proteus/proteus/__init__.py
+++ b/tryton/proteus/proteus/__init__.py
@@ -1152,9 +1152,8 @@
             values.update(self._on_change_args(on_change))
         if values:
             context = self._context
-            changes = getattr(self._proxy, 'on_change')(values, names, context)
-            for change in changes:
-                self._set_on_change(change)
+            change = getattr(self._proxy, 'on_change')(values, names, context)
+            self._set_on_change(change)
 
         values = {}
         fieldnames = set(names)
diff --git a/tryton/sao/src/model.js b/sao/src/model.js
index bfad1dc7382cb9fd2c17bef77da699ed36869d3e_c2FvL3NyYy9tb2RlbC5qcw==..bf7072adc76db4e62ec3fbde7efde17e7bbd630d_c2FvL3NyYy9tb2RlbC5qcw== 100644
--- a/tryton/sao/src/model.js
+++ b/tryton/sao/src/model.js
@@ -1071,5 +1071,5 @@
                                 [values], this.get_context(), false));
                         }
                     } else {
-                        changes = this.model.execute(
+                        changes = [this.model.execute(
                             'on_change',
@@ -1075,5 +1075,5 @@
                             'on_change',
-                            [values, fieldnames], this.get_context(), false);
+                            [values, fieldnames], this.get_context(), false)];
                     }
                 } catch (e) {
                     return;
@@ -1129,9 +1129,9 @@
                     delete this._values[fieldname + '.'];
                 }
             }
-            var result;
+            var changed;
             fieldnames = Object.keys(fieldnames);
             if (fieldnames.length) {
                 try {
                     if ((fieldnames.length == 1) ||
                         (values.id === undefined)) {
@@ -1133,7 +1133,7 @@
             fieldnames = Object.keys(fieldnames);
             if (fieldnames.length) {
                 try {
                     if ((fieldnames.length == 1) ||
                         (values.id === undefined)) {
-                        result = {};
+                        changed = {};
                         for (const fieldname of fieldnames) {
@@ -1139,6 +1139,8 @@
                         for (const fieldname of fieldnames) {
-                            result[fieldname] = this.model.execute(
-                                'on_change_with_' + fieldname,
-                                [values], this.get_context(), false);
+                            changed = jQuery.extend(
+                                changed,
+                                this.model.execute(
+                                    'on_change_with_' + fieldname,
+                                    [values], this.get_context(), false));
                         }
                     } else {
@@ -1143,9 +1145,9 @@
                         }
                     } else {
-                        result = this.model.execute(
+                        changed = this.model.execute(
                             'on_change_with',
                             [values, fieldnames], this.get_context(), false);
                     }
                 } catch (e) {
                     return;
                 }
@@ -1146,10 +1148,10 @@
                             'on_change_with',
                             [values, fieldnames], this.get_context(), false);
                     }
                 } catch (e) {
                     return;
                 }
-                this.set_on_change(result);
+                this.set_on_change(changed);
             }
             if (!jQuery.isEmptyObject(later)) {
                 values = {};
@@ -1164,5 +1166,5 @@
                 try {
                     if ((fieldnames.length == 1) ||
                         (values.id === undefined)) {
-                        result = {};
+                        changed = {};
                         for (const fieldname of fieldnames) {
@@ -1168,6 +1170,8 @@
                         for (const fieldname of fieldnames) {
-                            result[fieldname] = this.model.execute(
-                                'on_change_with_' + fieldname,
-                                [values], this.get_context(), false);
+                            changed = jQuery.extend(
+                                changed,
+                                this.model.execute(
+                                    'on_change_with_' + fieldname,
+                                    [values], this.get_context(), false));
                         }
                     } else {
@@ -1172,9 +1176,9 @@
                         }
                     } else {
-                        result = this.model.execute(
+                        changed = this.model.execute(
                             'on_change_with',
                             [values, fieldnames], this.get_context(), false);
                     }
                 } catch (e) {
                     return;
                 }
@@ -1175,10 +1179,10 @@
                             'on_change_with',
                             [values, fieldnames], this.get_context(), false);
                     }
                 } catch (e) {
                     return;
                 }
-                this.set_on_change(result);
+                this.set_on_change(changed);
             }
         },
         set_on_change: function(values) {
diff --git a/tryton/tryton/tryton/gui/window/view_form/model/record.py b/tryton/tryton/gui/window/view_form/model/record.py
index bfad1dc7382cb9fd2c17bef77da699ed36869d3e_dHJ5dG9uL3RyeXRvbi9ndWkvd2luZG93L3ZpZXdfZm9ybS9tb2RlbC9yZWNvcmQucHk=..bf7072adc76db4e62ec3fbde7efde17e7bbd630d_dHJ5dG9uL3RyeXRvbi9ndWkvd2luZG93L3ZpZXdfZm9ybS9tb2RlbC9yZWNvcmQucHk= 100644
--- a/tryton/tryton/tryton/gui/window/view_form/model/record.py
+++ b/tryton/tryton/tryton/gui/window/view_form/model/record.py
@@ -577,9 +577,9 @@
                                 'on_change_' + fieldname,
                                 values, context=self.get_context()))
                 else:
-                    changes = RPCExecute(
-                        'model', self.model_name, 'on_change',
-                        values, fieldnames, context=self.get_context())
+                    changes = [RPCExecute(
+                            'model', self.model_name, 'on_change',
+                            values, fieldnames, context=self.get_context())]
             except RPCException:
                 pass
             else:
@@ -621,5 +621,5 @@
         if fieldnames:
             try:
                 if len(fieldnames) == 1 or 'id' not in values:
-                    result = {}
+                    changed = {}
                     for fieldname in fieldnames:
@@ -625,6 +625,6 @@
                     for fieldname in fieldnames:
-                        result[fieldname] = RPCExecute(
-                            'model', self.model_name,
-                            'on_change_with_' + fieldname,
-                            values, context=self.get_context())
+                        changed.update(RPCExecute(
+                                'model', self.model_name,
+                                'on_change_with_' + fieldname,
+                                values, context=self.get_context()))
                 else:
@@ -630,6 +630,6 @@
                 else:
-                    result = RPCExecute(
+                    changed = RPCExecute(
                         'model', self.model_name, 'on_change_with',
                         values, list(fieldnames), context=self.get_context())
             except RPCException:
                 return
@@ -632,8 +632,8 @@
                         'model', self.model_name, 'on_change_with',
                         values, list(fieldnames), context=self.get_context())
             except RPCException:
                 return
-            self.set_on_change(result)
+            self.set_on_change(changed)
         if later:
             values = {}
             for fieldname in later:
@@ -642,5 +642,5 @@
                 values.update(self._get_on_change_args(on_change_with))
             try:
                 if len(later) == 1 or 'id' not in values:
-                    result = {}
+                    changed = {}
                     for fieldname in fieldnames:
@@ -646,6 +646,6 @@
                     for fieldname in fieldnames:
-                        result[fieldname] = RPCExecute(
-                            'model', self.model_name,
-                            'on_change_with_' + fieldname,
-                            values, context=self.get_context())
+                        changed.update(RPCExecute(
+                                'model', self.model_name,
+                                'on_change_with_' + fieldname,
+                                values, context=self.get_context()))
                 else:
@@ -651,6 +651,6 @@
                 else:
-                    result = RPCExecute(
+                    changed = RPCExecute(
                         'model', self.model_name, 'on_change_with',
                         values, list(later), context=self.get_context())
             except RPCException:
                 return
@@ -653,8 +653,8 @@
                         'model', self.model_name, 'on_change_with',
                         values, list(later), context=self.get_context())
             except RPCException:
                 return
-            self.set_on_change(result)
+            self.set_on_change(changed)
 
     def autocomplete_with(self, field_name):
         for fieldname, fieldinfo in self.group.fields.items():
diff --git a/tryton/trytond/doc/ref/rpc.rst b/trytond/doc/ref/rpc.rst
index bfad1dc7382cb9fd2c17bef77da699ed36869d3e_dHJ5dG9uZC9kb2MvcmVmL3JwYy5yc3Q=..bf7072adc76db4e62ec3fbde7efde17e7bbd630d_dHJ5dG9uZC9kb2MvcmVmL3JwYy5yc3Q= 100644
--- a/tryton/trytond/doc/ref/rpc.rst
+++ b/tryton/trytond/doc/ref/rpc.rst
@@ -4,7 +4,7 @@
 RPC
 ===
 
-.. class:: RPC([readonly[, instantiate[, result[, check_access[, unique[, fresh_session[, cache]]]]]]])
+.. class:: RPC([readonly[, instantiate[, [decorator, result[, check_access[, unique[, fresh_session[, cache]]]]]]]])
 
    Define the behavior of Remote Procedure Call.
 
@@ -18,6 +18,10 @@
 
    The position or the slice of the argument to be instanciated
 
+.. attribute:: RPC.decorator
+
+   The function to decorate the called procedure with
+
 .. attribute:: RPC.result
 
    The function to transform the result
diff --git a/tryton/trytond/trytond/model/fields/field.py b/trytond/trytond/model/fields/field.py
index bfad1dc7382cb9fd2c17bef77da699ed36869d3e_dHJ5dG9uZC90cnl0b25kL21vZGVsL2ZpZWxkcy9maWVsZC5weQ==..bf7072adc76db4e62ec3fbde7efde17e7bbd630d_dHJ5dG9uZC90cnl0b25kL21vZGVsL2ZpZWxkcy9maWVsZC5weQ== 100644
--- a/tryton/trytond/trytond/model/fields/field.py
+++ b/tryton/trytond/trytond/model/fields/field.py
@@ -1,7 +1,7 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
 import warnings
-from functools import partial, wraps
+from functools import wraps
 
 import sql
 from sql import (
@@ -195,18 +195,15 @@
     return record._changed_values
 
 
-def on_change_with_result(field, value):
-    from ..modelstorage import ModelStorage
-    if field._type in {'many2one', 'one2one', 'reference'}:
-        if isinstance(value, ModelStorage):
-            if field._type == 'reference':
-                value = str(value)
-            else:
-                value = value.id
-    elif field._type in {'one2many', 'many2many'}:
-        if isinstance(value, (list, tuple)):
-            value = [int(r) for r in value]
-    return value
+def on_change_with_result(fieldname):
+    def decorator(func):
+        @wraps(func)
+        def wrapper(self, *args, **kwargs):
+            value = func(self, *args, **kwargs)
+            setattr(self, fieldname, value)
+            return self._changed_values
+        return wrapper
+    return decorator
 
 
 def domain_method(func):
@@ -476,9 +473,9 @@
         return [self.sql_column(table)]
 
     def set_rpc(self, model):
-        for attribute, result in (
-                ('on_change', on_change_result),
-                ('on_change_with', partial(on_change_with_result, self)),
+        for attribute, decorator, result in (
+                ('on_change', None, on_change_result),
+                ('on_change_with', on_change_with_result(self.name), None),
                 ):
             if not getattr(self, attribute):
                 continue
@@ -486,7 +483,8 @@
             assert hasattr(model, func_name), \
                 'Missing %s on model %s' % (func_name, model.__name__)
             model.__rpc__.setdefault(
-                func_name, RPC(instantiate=0, result=result))
+                func_name,
+                RPC(instantiate=0, decorator=decorator, result=result))
 
     def definition(self, model, language):
         pool = Pool()
diff --git a/tryton/trytond/trytond/model/fields/function.py b/trytond/trytond/model/fields/function.py
index bfad1dc7382cb9fd2c17bef77da699ed36869d3e_dHJ5dG9uZC90cnl0b25kL21vZGVsL2ZpZWxkcy9mdW5jdGlvbi5weQ==..bf7072adc76db4e62ec3fbde7efde17e7bbd630d_dHJ5dG9uZC90cnl0b25kL21vZGVsL2ZpZWxkcy9mdW5jdGlvbi5weQ== 100644
--- a/tryton/trytond/trytond/model/fields/function.py
+++ b/tryton/trytond/trytond/model/fields/function.py
@@ -9,7 +9,7 @@
 from trytond.tools import is_instance_method
 from trytond.transaction import Transaction, without_check_access
 
-from .field import Field, domain_method, on_change_with_result
+from .field import Field, domain_method
 
 
 def getter_context(func):
@@ -124,5 +124,16 @@
 
         def call(name):
             if not instance_method:
-                return on_change_with_result(self, method(records, name))
+                values = method(records, name)
+                if isinstance(name, str):
+                    return convert_dict(values)
+                else:
+                    return {k: convert_dict(v, k) for k, v in values.items()}
+            else:
+                return {r.id: convert(method(r, name)) for r in records}
+
+        def convert(value, name=None):
+            from ..model import Model as BaseModel
+            if name:
+                field = Model._fields[name]._field
             else:
@@ -128,7 +139,22 @@
             else:
-                return {
-                    r.id: on_change_with_result(self, method(r, name))
-                    for r in records}
+                field = self._field
+            if field._type in {'many2one', 'one2one', 'reference'}:
+                if isinstance(value, BaseModel):
+                    if field._type == 'reference':
+                        value = str(value)
+                    else:
+                        value = int(value)
+            elif field._type in {'one2many', 'many2many'}:
+                if value:
+                    value = [int(r) for r in value]
+            return value
+
+        def convert_dict(values, name=None):
+            # Keep the same class
+            values = values.copy()
+            values.update((k, convert(v, name)) for k, v in values.items())
+            return values
+
         if isinstance(name, list):
             names = name
             if multiple:
diff --git a/tryton/trytond/trytond/model/modelview.py b/trytond/trytond/model/modelview.py
index bfad1dc7382cb9fd2c17bef77da699ed36869d3e_dHJ5dG9uZC90cnl0b25kL21vZGVsL21vZGVsdmlldy5weQ==..bf7072adc76db4e62ec3fbde7efde17e7bbd630d_dHJ5dG9uZC90cnl0b25kL21vZGVsL21vZGVsdmlldy5weQ== 100644
--- a/tryton/trytond/trytond/model/modelview.py
+++ b/tryton/trytond/trytond/model/modelview.py
@@ -68,8 +68,9 @@
         super(ModelView, cls).__setup__()
         cls.__rpc__['fields_view_get'] = RPC(cache=dict(days=1))
         cls.__rpc__['view_toolbar_get'] = RPC(cache=dict(days=1))
-        cls.__rpc__['on_change'] = RPC(instantiate=0)
-        cls.__rpc__['on_change_with'] = RPC(instantiate=0)
+        cls.__rpc__['on_change'] = RPC(instantiate=0, result=on_change_result)
+        cls.__rpc__['on_change_with'] = RPC(
+            instantiate=0, result=on_change_result)
         cls.__rpc__['on_change_notify'] = RPC(instantiate=0)
         cls._buttons = {}
 
@@ -758,8 +759,16 @@
             return func
         return decorator
 
+    @on_change
+    def on_change_with(self, fieldnames):
+        for fieldname in fieldnames:
+            method_name = 'on_change_with_%s' % fieldname
+            value = getattr(self, method_name)()
+            setattr(self, fieldname, value)
+
+    @on_change
     def on_change(self, fieldnames):
         for fieldname in sorted(fieldnames):
             method = getattr(self, 'on_change_%s' % fieldname, None)
             if method:
                 method()
@@ -761,34 +770,8 @@
     def on_change(self, fieldnames):
         for fieldname in sorted(fieldnames):
             method = getattr(self, 'on_change_%s' % fieldname, None)
             if method:
                 method()
-        # XXX remove backward compatibility
-        return [self._changed_values]
-
-    def on_change_with(self, fieldnames):
-        from .modelstorage import ModelStorage
-        changes = {}
-        for fieldname in fieldnames:
-            field = self._fields[fieldname]
-            method_name = 'on_change_with_%s' % fieldname
-            value = getattr(self, method_name)()
-            setattr(self, fieldname, value)
-            if field._type in {'many2one', 'one2one', 'reference'}:
-                if isinstance(value, ModelStorage):
-                    if value.id and value.id >= 0:
-                        changes[f'%{fieldname}.'] = {
-                            'rec_name': value.rec_name,
-                            }
-                    if field._type == 'reference':
-                        value = str(value)
-                    else:
-                        value = value.id
-            elif field._type in {'one2many', 'many2many'}:
-                if isinstance(value, (list, tuple)):
-                    value = [int(r) for r in value]
-            changes[fieldname] = value
-        return changes
 
     def on_change_notify(self):
         """Return a list of type and message couples.
@@ -802,8 +785,7 @@
         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 Many2Many: the list of ids
-            - for One2Many: a dictionary composed of three keys:
+            - 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`
@@ -822,7 +804,7 @@
             # Always test key presence in case value is None
             if (fname in init_values
                     and value == init_values[fname]
-                    and field._type != 'one2many'):
+                    and field._type not in {'one2many', 'many2many'}):
                 continue
             if field._type in ('many2one', 'one2one', 'reference'):
                 if value:
diff --git a/tryton/trytond/trytond/protocols/dispatcher.py b/trytond/trytond/protocols/dispatcher.py
index bfad1dc7382cb9fd2c17bef77da699ed36869d3e_dHJ5dG9uZC90cnl0b25kL3Byb3RvY29scy9kaXNwYXRjaGVyLnB5..bf7072adc76db4e62ec3fbde7efde17e7bbd630d_dHJ5dG9uZC90cnl0b25kL3Byb3RvY29scy9kaXNwYXRjaGVyLnB5 100644
--- a/tryton/trytond/trytond/protocols/dispatcher.py
+++ b/tryton/trytond/trytond/protocols/dispatcher.py
@@ -190,7 +190,7 @@
                 c_args, c_kwargs, transaction.context, transaction.timestamp \
                     = rpc.convert(obj, *args, **kwargs)
                 transaction.context['_request'] = request.context
-                meth = getattr(obj, method)
+                meth = rpc.decorate(getattr(obj, method))
                 if (rpc.instantiate is None
                         or not is_instance_method(obj, method)):
                     result = rpc.result(meth(*c_args, **c_kwargs))
diff --git a/tryton/trytond/trytond/rpc.py b/trytond/trytond/rpc.py
index bfad1dc7382cb9fd2c17bef77da699ed36869d3e_dHJ5dG9uZC90cnl0b25kL3JwYy5weQ==..bf7072adc76db4e62ec3fbde7efde17e7bbd630d_dHJ5dG9uZC90cnl0b25kL3JwYy5weQ== 100644
--- a/tryton/trytond/trytond/rpc.py
+++ b/tryton/trytond/trytond/rpc.py
@@ -18,8 +18,9 @@
     unique: Check instances are unique
     '''
 
-    __slots__ = ('readonly', 'instantiate', 'result', 'check_access',
-        'fresh_session', 'unique', 'cache')
+    __slots__ = (
+        'readonly', 'instantiate', 'decorator', 'result',
+        'check_access', 'fresh_session', 'unique', 'cache')
 
     def __init__(self, readonly=True, instantiate=None, result=None,
             check_access=True, fresh_session=False, unique=True, cache=None):
@@ -23,5 +25,6 @@
 
-    def __init__(self, readonly=True, instantiate=None, result=None,
+    def __init__(
+            self, readonly=True, instantiate=None, decorator=None, result=None,
             check_access=True, fresh_session=False, unique=True, cache=None):
         self.readonly = readonly
         self.instantiate = instantiate
@@ -25,6 +28,7 @@
             check_access=True, fresh_session=False, unique=True, cache=None):
         self.readonly = readonly
         self.instantiate = instantiate
+        self.decorator = decorator
         if result is None:
             def result(r):
                 return r
@@ -83,6 +87,11 @@
             context['_check_access'] = True
         return args, kwargs, context, timestamp
 
+    def decorate(self, func):
+        if self.decorator:
+            func = self.decorator(func)
+        return func
+
 
 class RPCCache:
     __slots__ = ('duration',)
diff --git a/tryton/trytond/trytond/tests/test_field_function.py b/trytond/trytond/tests/test_field_function.py
index bfad1dc7382cb9fd2c17bef77da699ed36869d3e_dHJ5dG9uZC90cnl0b25kL3Rlc3RzL3Rlc3RfZmllbGRfZnVuY3Rpb24ucHk=..bf7072adc76db4e62ec3fbde7efde17e7bbd630d_dHJ5dG9uZC90cnl0b25kL3Rlc3RzL3Rlc3RfZmllbGRfZnVuY3Rpb24ucHk= 100644
--- a/tryton/trytond/trytond/tests/test_field_function.py
+++ b/tryton/trytond/trytond/tests/test_field_function.py
@@ -103,7 +103,7 @@
 
         record = Model()
         record.save()
-        with patch.object(Model, 'get_function1') as getter:
+        with patch.object(Model, 'get_function1', autospec=True) as getter:
             getter.return_value = 'test'
 
             Model.read([record.id], ['function1', 'function2'])