GH-512: allow foreign key to reference self using self str (#513)

* GH-512: Fix bug that disallowed using 'self' str when creating ForeignKey to self

* Formatted

* Updated CHANGES.rst

* last change

* Fixed missing on_delete

Author: Ross Mechanic

CHANGES.rst

@@ -6,6 +6,7 @@ Unreleased
 - Add support for `using` chained manager method and save/delete keyword argument (gh-507)
 - Added management command `clean_duplicate_history` to remove duplicate history entries (gh-483)
 - Updated most_recent to work with excluded_fields (gh-477)
+- Fixed bug that prevented self-referential foreign key from using `'self'` (gh-513)
 
 2.6.0 (2018-12-12)
 ------------------

simple_history/models.py

@@ -213,6 +213,13 @@ def copy_fields(self, model):
                 else:
                     FieldType = type(old_field)
 
+                # If field_args['to'] is 'self' then we have a case where the object
+                # has a foreign key to itself. If we pass the historical record's
+                # field to = 'self', the foreign key will point to an historical
+                # record rather than the base record. We can use old_field.model here.
+                if field_args.get("to", None) == "self":
+                    field_args["to"] = old_field.model
+
                 # Override certain arguments passed when creating the field
                 # so that they work for the historical field.
                 field_args.update(

simple_history/tests/models.py

@@ -553,3 +553,13 @@ class CustomNameModel(models.Model):
 class CustomManagerNameModel(models.Model):
     name = models.CharField(max_length=15)
     log = HistoricalRecords()
+
+
+class ForeignKeyToSelfModel(models.Model):
+    fk_to_self = models.ForeignKey(
+        "ForeignKeyToSelfModel", null=True, related_name="+", on_delete=models.CASCADE
+    )
+    fk_to_self_using_str = models.ForeignKey(
+        "self", null=True, related_name="+", on_delete=models.CASCADE
+    )
+    history = HistoricalRecords()

simple_history/tests/tests/test_models.py

@@ -1,6 +1,7 @@
 from __future__ import unicode_literals
 
 import unittest
+
 import uuid
 import warnings
 from datetime import datetime, timedelta
@@ -43,6 +44,7 @@
     ExternalModel1,
     ExternalModel3,
     FileModel,
+    ForeignKeyToSelfModel,
     HistoricalChoice,
     HistoricalCustomFKError,
     HistoricalPoll,
@@ -583,7 +585,6 @@ def setUp(self):
         self.poll.save()
 
     def test_get_prev_record(self):
-
         self.poll.question = "ask questions?"
         self.poll.save()
         self.poll.question = "eh?"
@@ -1203,7 +1204,6 @@ def test_signal_is_able_to_retrieve_request_from_thread(self):
 
 class WarningOnAbstractModelWithInheritFalseTest(TestCase):
     def test_warning_on_abstract_model_with_inherit_false(self):
-
         with warnings.catch_warnings(record=True) as w:
 
             class AbstractModelWithInheritFalse(models.Model):
@@ -1224,7 +1224,6 @@ class Meta:
 
 
 class MultiDBWithUsingTest(TestCase):
-
     """Asserts historical manager respects `using()` and the `using`
     keyword argument in `save()`.
     """
@@ -1309,3 +1308,19 @@ def test_multidb_with_using_keyword_in_save_and_delete(self):
                 .order_by("history_date")
             ],
         )
+
+
+class ForeignKeyToSelfTest(TestCase):
+    def setUp(self):
+        self.model = ForeignKeyToSelfModel
+        self.history_model = self.model.history.model
+
+    def test_foreign_key_to_self_using_model_str(self):
+        self.assertEqual(
+            self.model, self.history_model.fk_to_self.field.remote_field.model
+        )
+
+    def test_foreign_key_to_self_using_self_str(self):
+        self.assertEqual(
+            self.model, self.history_model.fk_to_self_using_str.field.remote_field.model
+        )