Allow the use of multiple databases (#539)

* create historical record in the table associated with the historical record's table

* cleanup

* override using argument

* format

* docs

* tests

* multi db support

* fixed conflicts

* test-only class needs Meta attribute for migrations to apply to separate database

* updated docs with multiple db testing information

* more tests to ensure that queries on historical models in separate dbs are still possible

* use_base_model_db

* Fixed tests

* updated docs with use_base_model_db

Author: dopatraman

AUTHORS.rst

@@ -70,6 +70,7 @@ Authors
 - Nianpeng Li
 - Nick Träger
 - Phillip Marshall
+- Prakash Venkatraman (`dopatraman <https://github.com/dopatraman>`_)
 - Rajesh Pappula
 - Ray Logel
 - Roberto Aguilar

CHANGES.rst

@@ -8,6 +8,10 @@ Unreleased
 ----------
 - Added the possibility to create a relation to the original model
 
+2.7.1 (2019-03-26)
+------------------
+- Added routing for saving historical records to separate databases if necessary.
+
 2.7.0 (2019-01-16)
 ------------------
 - Add support for ``using`` chained manager method and save/delete keyword argument (gh-507)

docs/multiple_dbs.rst

@@ -39,3 +39,18 @@ an issue where you want to track the history on a table that lives in a separate
 database to your user model. Since Django does not support cross-database relations,
 you will have to manually track the ``history_user`` using an explicit ID. The full
 documentation on this feature is in :ref:`Manually Track User Model`.
+
+Tracking History Separate from the Base Model
+---------------------------------------------
+You can choose whether or not to track models' history in the same database by
+setting the flag `use_base_model_db`.
+
+```
+class MyModel(models.Model):
+    ...
+    history = HistoricalRecords(use_base_model_db=False)
+```
+
+If set to `True`, migrations and audit
+events will be sent to the same database as the base model. If `False`, they
+will be sent to the place specified by the database router.

simple_history/models.py

@@ -79,6 +79,7 @@ def __init__(
         history_user_getter=_history_user_getter,
         history_user_setter=_history_user_setter,
         related_name=None,
+        use_base_model_db=True,
     ):
         self.user_set_verbose_name = verbose_name
         self.user_related_name = user_related_name
@@ -95,6 +96,7 @@ def __init__(
         self.user_getter = history_user_getter
         self.user_setter = history_user_setter
         self.related_name = related_name
+        self.use_base_model_db = use_base_model_db
 
         if excluded_fields is None:
             excluded_fields = []
@@ -433,14 +435,20 @@ def post_save(self, instance, created, using=None, **kwargs):
         if not created and hasattr(instance, "skip_history_when_saving"):
             return
         if not kwargs.get("raw", False):
-            self.create_historical_record(instance, created and "+" or "~", using=using)
+            self.create_historical_record(
+                instance,
+                created and "+" or "~",
+                using=using if self.use_base_model_db else None,
+            )
 
     def post_delete(self, instance, using=None, **kwargs):
         if self.cascade_delete_history:
             manager = getattr(instance, self.manager_name)
             manager.using(using).all().delete()
         else:
-            self.create_historical_record(instance, "-", using=using)
+            self.create_historical_record(
+                instance, "-", using=using if self.use_base_model_db else None
+            )
 
     def create_historical_record(self, instance, history_type, using=None):
         history_date = getattr(instance, "_history_date", now())

simple_history/tests/models.py

@@ -362,6 +362,11 @@ class ModelWithHistoryInDifferentApp(models.Model):
     history = HistoricalRecords(app="external")
 
 
+class ModelWithHistoryInDifferentDb(models.Model):
+    name = models.CharField(max_length=30)
+    history = HistoricalRecords(use_base_model_db=False)
+
+
 ###############################################################################
 #
 # Inheritance examples

simple_history/tests/tests/test_models.py

@@ -18,11 +18,15 @@
 from simple_history import register
 from simple_history.exceptions import RelatedNameConflictError
 from simple_history.models import HistoricalRecords, ModelChange
-from simple_history.signals import pre_create_historical_record
+from simple_history.signals import (
+    pre_create_historical_record,
+    post_create_historical_record,
+)
 from simple_history.tests.custom_user.models import CustomUser
 from simple_history.tests.tests.utils import (
     database_router_override_settings,
     middleware_override_settings,
+    database_router_override_settings_history_in_diff_db,
 )
 from simple_history.utils import get_history_model_for_model
 from simple_history.utils import update_change_reason
@@ -62,6 +66,7 @@
     HistoricalPollWithHistoricalIPAddress,
     HistoricalState,
     Library,
+    ModelWithHistoryInDifferentDb,
     MultiOneToOne,
     Person,
     Place,
@@ -1478,3 +1483,46 @@ def test_revert(self):
 
         self.one = Street.objects.get(pk=id)
         self.assertEqual(self.one.history.count(), 4)
+
+
+@override_settings(**database_router_override_settings_history_in_diff_db)
+class SaveHistoryInSeparateDatabaseTestCase(TestCase):
+    multi_db = True
+
+    def setUp(self):
+        self.model = ModelWithHistoryInDifferentDb.objects.create(name="test")
+
+    def test_history_model_saved_in_separate_db(self):
+        self.assertEqual(0, self.model.history.using("default").count())
+        self.assertEqual(1, self.model.history.count())
+        self.assertEqual(1, self.model.history.using("other").count())
+        self.assertEqual(
+            1, ModelWithHistoryInDifferentDb.objects.using("default").count()
+        )
+        self.assertEqual(1, ModelWithHistoryInDifferentDb.objects.count())
+        self.assertEqual(
+            0, ModelWithHistoryInDifferentDb.objects.using("other").count()
+        )
+
+    def test_history_model_saved_in_separate_db_on_delete(self):
+        id = self.model.id
+        self.model.delete()
+
+        self.assertEqual(
+            0,
+            ModelWithHistoryInDifferentDb.history.using("default")
+            .filter(id=id)
+            .count(),
+        )
+        self.assertEqual(2, ModelWithHistoryInDifferentDb.history.filter(id=id).count())
+        self.assertEqual(
+            2,
+            ModelWithHistoryInDifferentDb.history.using("other").filter(id=id).count(),
+        )
+        self.assertEqual(
+            0, ModelWithHistoryInDifferentDb.objects.using("default").count()
+        )
+        self.assertEqual(0, ModelWithHistoryInDifferentDb.objects.count())
+        self.assertEqual(
+            0, ModelWithHistoryInDifferentDb.objects.using("other").count()
+        )

simple_history/tests/tests/utils.py

@@ -1,8 +1,12 @@
 import django
 from django.conf import settings
 
+from simple_history.tests.models import HistoricalModelWithHistoryInDifferentDb
+
 request_middleware = "simple_history.middleware.HistoryRequestMiddleware"
 
+OTHER_DB_NAME = "other"
+
 if django.__version__ >= "2.0":
     middleware_override_settings = {
         "MIDDLEWARE": (settings.MIDDLEWARE + [request_middleware])
@@ -16,12 +20,12 @@
 class TestDbRouter(object):
     def db_for_read(self, model, **hints):
         if model._meta.app_label == "external":
-            return "other"
+            return OTHER_DB_NAME
         return None
 
     def db_for_write(self, model, **hints):
         if model._meta.app_label == "external":
-            return "other"
+            return OTHER_DB_NAME
         return None
 
     def allow_relation(self, obj1, obj2, **hints):
@@ -31,8 +35,8 @@ def allow_relation(self, obj1, obj2, **hints):
 
     def allow_migrate(self, db, app_label, model_name=None, **hints):
         if app_label == "external":
-            return db == "other"
-        elif db == "other":
+            return db == OTHER_DB_NAME
+        elif db == OTHER_DB_NAME:
             return False
         else:
             return None
@@ -41,3 +45,34 @@ def allow_migrate(self, db, app_label, model_name=None, **hints):
 database_router_override_settings = {
     "DATABASE_ROUTERS": ["simple_history.tests.tests.utils.TestDbRouter"]
 }
+
+
+class TestModelWithHistoryInDifferentDbRouter(object):
+    def db_for_read(self, model, **hints):
+        if model == HistoricalModelWithHistoryInDifferentDb:
+            return OTHER_DB_NAME
+        return None
+
+    def db_for_write(self, model, **hints):
+        if model == HistoricalModelWithHistoryInDifferentDb:
+            return OTHER_DB_NAME
+        return None
+
+    def allow_relation(self, obj1, obj2, **hints):
+        if isinstance(obj1, HistoricalModelWithHistoryInDifferentDb) or isinstance(
+            obj2, HistoricalModelWithHistoryInDifferentDb
+        ):
+            return False
+        return None
+
+    def allow_migrate(self, db, app_label, model_name=None, **hints):
+        if model_name == HistoricalModelWithHistoryInDifferentDb._meta.model_name:
+            return db == OTHER_DB_NAME
+        return None
+
+
+database_router_override_settings_history_in_diff_db = {
+    "DATABASE_ROUTERS": [
+        "simple_history.tests.tests.utils.TestModelWithHistoryInDifferentDbRouter"
+    ]
+}