Use django builtin for determining through field name

Fixes #1126

AUTHORS.rst

@@ -89,6 +89,7 @@ Authors
 - Lucas Wiman
 - Maciej "RooTer" Urbański
 - Marcelo Canina (`marcanuy <https://github.com/marcanuy>`_)
+- Marco Sirabella
 - Mark Davidoff
 - Martin Bachwerk
 - Marty Alchin

CHANGES.rst

@@ -9,6 +9,7 @@ Unreleased
   ``SIMPLE_HISTORY_ENFORCE_HISTORY_MODEL_PERMISSIONS`` is set to ``True``
   in ``settings`` (gh-1017).
 - Fixed ``SimpleHistoryAdmin`` not properly integrating with custom user models (gh-1177)
+- Fixes self-m2m fields not using the correct through field name (gh-1218)
 
 3.3.0 (2023-03-08)
 ------------------

simple_history/models.py

@@ -668,7 +668,7 @@ def create_historical_record_m2ms(self, history_instance, instance):
 
             insert_rows = []
 
-            through_field_name = type(original_instance).__name__.lower()
+            through_field_name = field.m2m_field_name()
 
             rows = through_model.objects.filter(**{through_field_name: instance})
 

simple_history/tests/models.py

@@ -200,6 +200,11 @@ class PollChildRestaurantWithManyToMany(PollParentWithManyToMany):
     _history_m2m_fields = [restaurants]
 
 
+class PollWithSelfManyToMany(models.Model):
+    relations = models.ManyToManyField("self")
+    history = HistoricalRecords(m2m_fields=[relations])
+
+
 class CustomAttrNameForeignKey(models.ForeignKey):
     def __init__(self, *args, **kwargs):
         self.attr_name = kwargs.pop("attr_name", None)

simple_history/tests/tests/test_models.py

@@ -103,6 +103,7 @@
     PollWithManyToManyCustomHistoryID,
     PollWithManyToManyWithIPAddress,
     PollWithNonEditableField,
+    PollWithSelfManyToMany,
     PollWithSeveralManyToMany,
     Province,
     Restaurant,
@@ -1851,6 +1852,11 @@ def test_separation(self):
         self.assertEqual(add.restaurants.all().count(), 0)
         self.assertEqual(add.places.all().count(), 0)
 
+    def test_self_field(self):
+        poll1 = PollWithSelfManyToMany.objects.create()
+        poll2 = PollWithSelfManyToMany.objects.create()
+        poll1.relations.add(poll2)
+
 
 class ManyToManyWithSignalsTest(TestCase):
     def setUp(self):