Try to invalidate m2m in more robust way

cacheops/query.py

@@ -536,19 +536,23 @@ def invalidate_m2m(sender=None, instance=None, model=None, action=None, pk_set=N
     if not sender._meta.auto_created:
         return
 
+    for m2m in instance._meta.many_to_many:
+        if m2m.rel.through == sender:
+            field_name = m2m.m2m_field_name()
+            column_name = m2m.m2m_column_name()
+            reverse_column_name = m2m.m2m_reverse_name()
+
     # TODO: optimize several invalidate_objs/dicts at once
     if action == 'pre_clear':
-        attname = get_model_name(instance)
-        objects = sender.objects.filter(**{attname: instance.pk})
+        objects = sender.objects.filter(**{field_name: instance.pk})
         for obj in objects:
             invalidate_obj(obj)
     elif action in ('post_add', 'pre_remove'):
-        # NOTE: we don't need to query through objects here,
-        #       cause we already know all their meaningful attributes.
-        base_att = get_model_name(instance) + '_id'
-        item_att = get_model_name(model) + '_id'
+        # NOTE: we don't need to query thorugh objects here,
+        #       cause we already know all their meaningfull attributes.
         for pk in pk_set:
-            invalidate_dict(sender, {base_att: instance.pk, item_att: pk})
+            invalidate_dict(sender, {column_name: instance.pk,
+                                     reverse_column_name: pk})
 
 
 @once

tests/models.py

@@ -150,6 +150,8 @@ class Labeling(models.Model):
     brand = models.ForeignKey(BrandT)
     tag = models.IntegerField()
 
+class PremiumBrand(Brand):
+    extra = models.CharField(max_length=127, blank=True, default='')
 
 # local_get
 class Local(models.Model):

tests/tests.py

@@ -517,6 +517,21 @@ def test_base_invalidates_on_remove(self):
             lambda: self.bf.labels.remove(self.furious)
         )
 
+class MultiTableInheritanceWithM2MTest(M2MTests):
+
+    def setUp(self):
+        self.bf = PremiumBrand.objects.create()
+        self.bs = PremiumBrand.objects.create()
+
+        self.fast = Label.objects.create(text='fast')
+        self.slow = Label.objects.create(text='slow')
+        self.furious = Label.objects.create(text='furios')
+
+        self.bf.labels.add(self.fast, self.furious)
+        self.bs.labels.add(self.slow, self.furious)
+
+        super(M2MTests, self).setUp()
+
 
 class M2MThroughTests(M2MTests):
     brand_cls = BrandT