Remove db constraint on historical user to prevent IntegrityError (#676)

* Remove db constraint on historical user to prevent IntegrityError when deleting user

* added ``user_db_constraint`` param to history to avoid circular reference on delete (gh-676)

* Move user_db_constraint to bottom parameter

Author: keithhackbarth

AUTHORS.rst

@@ -60,6 +60,7 @@ Authors
 - Jonathan Sanchez
 - Jonathan Zvesper (`zvesp <https://github.com/zvesp>`_)
 - Josh Fyne
+- Keith Hackbarth
 - Kevin Foster
 - Klaas van Schelven
 - Kris Neuharth

CHANGES.rst

@@ -1,6 +1,7 @@
 Changes
 =======
 2.10.1 (2020-06-16)
+- added ``user_db_constraint`` param to history to avoid circular reference on delete (gh-676)
 - added ``clean_old_history`` management command (gh-675)
 
 2.10.0 (2020-04-27)

simple_history/models.py

@@ -82,9 +82,11 @@ def __init__(
         history_user_setter=_history_user_setter,
         related_name=None,
         use_base_model_db=False,
+        user_db_constraint=True,
     ):
         self.user_set_verbose_name = verbose_name
         self.user_related_name = user_related_name
+        self.user_db_constraint = user_db_constraint
         self.table_name = table_name
         self.inherit = inherit
         self.history_id_field = history_id_field
@@ -342,6 +344,7 @@ def _get_history_user_fields(self):
                     null=True,
                     related_name=self.user_related_name,
                     on_delete=models.SET_NULL,
+                    db_constraint=self.user_db_constraint,
                 )
             }
 

simple_history/tests/models.py

@@ -214,7 +214,10 @@ class Document(models.Model):
 
     @property
     def _history_user(self):
-        return self.changed_by
+        try:
+            return self.changed_by
+        except User.DoesNotExist:
+            return None
 
 
 class Paper(Document):

simple_history/tests/tests/test_models.py

@@ -370,6 +370,32 @@ def test_specify_history_user(self):
             [d.history_user for d in document.history.all()], [None, user2, user1]
         )
 
+    def test_specify_history_user_self_reference_delete(self):
+        user1 = User.objects.create_user("user1", "[email protected]")
+        user2 = User.objects.create_user("user2", "[email protected]")
+        document = Document.objects.create(changed_by=user1)
+        document.changed_by = user2
+        document.save()
+        document.changed_by = None
+        document.save()
+        self.assertEqual(
+            [d.history_user for d in document.history.all()], [None, user2, user1]
+        )
+
+        # Change back to user1
+        document.changed_by = user1
+        document.save()
+
+        # Deleting user1 will cascade delete the document,
+        # but fails when it tries to make the historical
+        # record for the deleted user1.
+        # This test performs differently on Postgres vs. SQLite
+        # because of how the two database handle database constraints
+        try:
+            user1.delete()
+        except IntegrityError as e:
+            self.fail(e)
+
     def test_specify_history_date_1(self):
         temperature = Temperature.objects.create(
             location="London", temperature=14, _history_date=today
@@ -398,7 +424,7 @@ def test_non_default_primary_key_save(self):
         library.book = None
         library.save()
         self.assertEqual(
-            [l.book_id for l in library.history.all()], [None, book2.pk, book1.pk]
+            [lib.book_id for lib in library.history.all()], [None, book2.pk, book1.pk]
         )
 
     def test_string_defined_foreign_key_save(self):