Fixed #12337 - Honor ModelForm.Meta.exclude when saving ManyToManyFields.

Thanks margieroginski for the report.

django/forms/models.py

@@ -85,6 +85,8 @@ def save_instance(form, instance, fields=None, fail_message='saved',
         for f in opts.many_to_many:
             if fields and f.name not in fields:
                 continue
+            if exclude and f.name in exclude:
+                continue
             if f.name in cleaned_data:
                 f.save_form_data(instance, cleaned_data[f.name])
     if commit:
@@ -405,7 +407,8 @@ class BaseModelForm(BaseForm):
         else:
             fail_message = 'changed'
         return save_instance(self, self.instance, self._meta.fields,
-                             fail_message, commit, construct=False)
+                             fail_message, commit, self._meta.exclude,
+                             construct=False)
 
     save.alters_data = True
 

tests/forms_tests/tests/tests.py

@@ -5,7 +5,7 @@ import datetime
 
 from django.core.files.uploadedfile import SimpleUploadedFile
 from django.db import models
-from django.forms import Form, ModelForm, FileField, ModelChoiceField
+from django.forms import Form, ModelForm, FileField, ModelChoiceField, CharField
 from django.forms.models import ModelFormMetaclass
 from django.test import TestCase
 from django.utils import six
@@ -26,6 +26,14 @@ class OptionalMultiChoiceModelForm(ModelForm):
         fields = '__all__'
 
 
+class ChoiceFieldExclusionForm(ModelForm):
+    multi_choice = CharField(max_length=50)
+
+    class Meta:
+        exclude = ['multi_choice']
+        model = ChoiceFieldModel
+
+
 class FileForm(Form):
     file1 = FileField()
 
@@ -221,3 +229,31 @@ class RelatedModelFormTests(TestCase):
             model=A
 
         self.assertTrue(issubclass(ModelFormMetaclass(str('Form'), (ModelForm,), {'Meta': Meta}), ModelForm))
+
+
+class ManyToManyExclusionTestCase(TestCase):
+    def test_m2m_field_exclusion(self):
+        # Issue 12337. save_instance should honor the passed-in exclude keyword.
+        opt1 = ChoiceOptionModel.objects.create(id=1, name='default')
+        opt2 = ChoiceOptionModel.objects.create(id=2, name='option 2')
+        opt3 = ChoiceOptionModel.objects.create(id=3, name='option 3')
+        initial = {
+            'choice': opt1,
+            'choice_int': opt1,
+        }
+        data = {
+            'choice': opt2.pk,
+            'choice_int': opt2.pk,
+            'multi_choice': 'string data!',
+            'multi_choice_int': [opt1.pk],
+        }
+        instance = ChoiceFieldModel.objects.create(**initial)
+        instance.multi_choice = instance.multi_choice_int = [opt2, opt3]
+        form = ChoiceFieldExclusionForm(data=data, instance=instance)
+        self.assertTrue(form.is_valid())
+        self.assertEqual(form.cleaned_data['multi_choice'], data['multi_choice'])
+        form.save()
+        self.assertEqual(form.instance.choice.pk, data['choice'])
+        self.assertEqual(form.instance.choice_int.pk, data['choice_int'])
+        self.assertEqual(list(form.instance.multi_choice.all()), [opt2, opt3])
+        self.assertEqual([obj.pk for obj in form.instance.multi_choice_int.all()], data['multi_choice_int'])