Update M2M check mode to be disabled by default

src/dirtyfields/dirtyfields.py

@@ -14,7 +14,7 @@ class DirtyFieldsMixin(object):
 
     # This mode has been introduced to handle some situations like this one:
     # https://github.com/romgar/django-dirtyfields/issues/73
-    ENABLE_M2M_CHECK = True
+    ENABLE_M2M_CHECK = False
 
     def __init__(self, *args, **kwargs):
         super(DirtyFieldsMixin, self).__init__(*args, **kwargs)

tests/models.py

@@ -68,6 +68,11 @@ class TestCurrentDatetimeModel(DirtyFieldsMixin, models.Model):
 
 class TestM2MModel(DirtyFieldsMixin, models.Model):
     m2m_field = models.ManyToManyField(TestModel)
+    ENABLE_M2M_CHECK = True
+
+
+class TestM2MModelWithoutM2MModeEnabled(DirtyFieldsMixin, models.Model):
+    m2m_field = models.ManyToManyField(TestModel)
 
 
 class TestModelWithCustomPK(DirtyFieldsMixin, models.Model):

tests/test_m2m_fields.py

@@ -1,7 +1,7 @@
 import pytest
 
 from .models import TestModel, TestM2MModel, TestModelWithCustomPK, TestM2MModelWithCustomPKOnM2M, \
-    TestModelWithoutM2MCheck
+    TestModelWithoutM2MCheck, TestM2MModelWithoutM2MModeEnabled
 
 
 @pytest.mark.django_db
@@ -23,6 +23,16 @@ def test_dirty_fields_on_m2m():
     assert tm.get_dirty_fields(check_m2m={'m2m_field': set([0, tm2.id])}) == {'m2m_field': set([tm2.id])}
 
 
+@pytest.mark.django_db
+def test_dirty_fields_on_m2m_not_possible_if_not_enabled():
+    tm = TestM2MModelWithoutM2MModeEnabled.objects.create()
+    tm2 = TestModel.objects.create()
+    tm.m2m_field.add(tm2)
+
+    with pytest.raises(Exception):
+        assert tm.get_dirty_fields(check_m2m={'m2m_field': set([tm2.id])}) == {}
+
+
 @pytest.mark.django_db
 def test_m2m_check_with_custom_primary_key():
     # test for bug: https://github.com/romgar/django-dirtyfields/issues/74