Provide history_id_field to change the field type for history_id (#368)

* Provide history_id_field to change the field type for history_id

* Updates based on review comments

* Add SIMPLE_HISTORY_HISTORY_ID_DEFAULT_FIELD setting

* Change setting to SIMPLE_HISTORY_HISTORY_ID_USE_UUID

* Update CHANGES

Author: rwlogel

CHANGES.rst

@@ -1,6 +1,10 @@
 Changes
 =======
 
+Unreleased
+----------
+- Add ability to specify custom history_id field (gh-368)
+
 2.0 (2018-04-05)
 ----------------
 - Added Django 2.0 support (gh-330)

docs/advanced.rst

@@ -127,6 +127,37 @@ referencing the ``changed_by`` field:
 
 Admin integration requires that you use a ``_history_user.setter`` attribute with your custom ``_history_user`` property (see :ref:`admin_integration`).
 
+Custom ``history_id``
+---------------------
+
+By default, the historical table of a model will use an ``AutoField`` for the table's
+``history_id`` (the history table's primary key). However, you can specify a different
+type of field for ``history_id`` buy passing a different field to ``history_id_field``
+parameter.
+
+A common use case for this would be to use a ``UUIDField``.  If you want to use a ``UUIDField``
+as the default for all classes set ``SIMPLE_HISTORY_HISTORY_ID_USE_UUID=True`` in the settings.
+This setting can still be overridden using the ``history_id_field`` parameter on a per model basis.
+
+You can use the ``history_id_field`` parameter with both ``HistoricalRecords()`` or
+``register()`` to change this behavior.
+
+Note: regardless of what field type you specify as your history_id field, that field will
+automatically set ``primary_key=True`` and ``editable=False``.
+
+.. code-block:: python
+
+    import uuid
+    from django.db import models
+    from simple_history.models import HistoricalRecords
+
+    class Poll(models.Model):
+        question = models.CharField(max_length=200)
+        pub_date = models.DateTimeField('date published')
+        history = HistoricalRecords(
+            history_id_field=models.UUIDField(default=uuid.uuid4)
+        )
+
 
 Custom ``history_date``
 -----------------------

simple_history/models.py

@@ -3,6 +3,7 @@
 import copy
 import importlib
 import threading
+import uuid
 
 from django.apps import apps
 from django.conf import settings
@@ -27,11 +28,13 @@ class HistoricalRecords(object):
 
     def __init__(self, verbose_name=None, bases=(models.Model,),
                  user_related_name='+', table_name=None, inherit=False,
+                 history_id_field=None,
                  excluded_fields=None):
         self.user_set_verbose_name = verbose_name
         self.user_related_name = user_related_name
         self.table_name = table_name
         self.inherit = inherit
+        self.history_id_field = history_id_field
         if excluded_fields is None:
             excluded_fields = []
         self.excluded_fields = excluded_fields
@@ -219,8 +222,19 @@ def get_instance(self):
                 for field in fields.values()
             })
 
+        if self.history_id_field:
+            history_id_field = self.history_id_field
+            history_id_field.primary_key = True
+            history_id_field.editable = False
+        elif getattr(settings, 'SIMPLE_HISTORY_HISTORY_ID_USE_UUID', False):
+            history_id_field = models.UUIDField(
+                primary_key=True, default=uuid.uuid4, editable=False
+            )
+        else:
+            history_id_field = models.AutoField(primary_key=True)
+
         return {
-            'history_id': models.AutoField(primary_key=True),
+            'history_id': history_id_field,
             'history_date': models.DateTimeField(),
             'history_change_reason': models.CharField(max_length=100,
                                                       null=True),

simple_history/registry_tests/tests.py

@@ -1,6 +1,7 @@
 from __future__ import unicode_literals
 
 import unittest
+import uuid
 from datetime import datetime, timedelta
 
 from django.apps import apps
@@ -15,7 +16,7 @@
                             Restaurant, TrackedAbstractBaseA,
                             TrackedAbstractBaseB, TrackedWithAbstractBase,
                             TrackedWithConcreteBase, UserAccessorDefault,
-                            UserAccessorOverride, Voter)
+                            UserAccessorOverride, UUIDRegisterModel, Voter)
 
 get_model = apps.get_model
 User = get_user_model()
@@ -56,6 +57,13 @@ def test_register_custome_records(self):
         self.assertEqual(expected,
                          str(voter.history.all()[0])[:len(expected)])
 
+    def test_register_history_id_field(self):
+        self.assertEqual(len(UUIDRegisterModel.history.all()), 0)
+        entry = UUIDRegisterModel.objects.create()
+        self.assertEqual(len(entry.history.all()), 1)
+        history = entry.history.all()[0]
+        self.assertTrue(isinstance(history.history_id, uuid.UUID))
+
 
 class TestUserAccessor(unittest.TestCase):
 

simple_history/tests/models.py

@@ -1,6 +1,9 @@
 from __future__ import unicode_literals
 
+import uuid
+
 from django.apps import apps
+from django.conf import settings
 from django.db import models
 from django.urls import reverse
 
@@ -401,3 +404,31 @@ class InheritTracking3(BaseInheritTracking3):
 
 class InheritTracking4(TrackedAbstractBaseA):
     pass
+
+
+class UUIDModel(models.Model):
+    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+    history = HistoricalRecords(
+        history_id_field=models.UUIDField(default=uuid.uuid4)
+    )
+
+
+class UUIDRegisterModel(models.Model):
+    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+
+
+register(UUIDRegisterModel,
+         history_id_field=models.UUIDField(default=uuid.uuid4))
+
+
+# Set the SIMPLE_HISTORY_HISTORY_ID_USE_UUID
+setattr(settings, 'SIMPLE_HISTORY_HISTORY_ID_USE_UUID', True)
+
+
+class UUIDDefaultModel(models.Model):
+    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+    history = HistoricalRecords()
+
+
+# Clear the SIMPLE_HISTORY_HISTORY_ID_USE_UUID
+delattr(settings, 'SIMPLE_HISTORY_HISTORY_ID_USE_UUID')

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
 
@@ -50,6 +51,8 @@
     State,
     Temperature,
     UnicodeVerboseName,
+    UUIDModel,
+    UUIDDefaultModel,
     WaterLevel
 )
 
@@ -367,6 +370,18 @@ def test_model_with_excluded_fields(self):
         self.assertIn('question', all_fields_names)
         self.assertNotIn('pub_date', all_fields_names)
 
+    def test_uuid_history_id(self):
+        entry = UUIDModel.objects.create()
+
+        history = entry.history.all()[0]
+        self.assertTrue(isinstance(history.history_id, uuid.UUID))
+
+    def test_uuid_default_history_id(self):
+        entry = UUIDDefaultModel.objects.create()
+
+        history = entry.history.all()[0]
+        self.assertTrue(isinstance(history.history_id, uuid.UUID))
+
 
 class CreateHistoryModelTests(unittest.TestCase):