Issue 720 no db indices (#782)

* implemented a register setting that allows you to drop db_index on history models, tests are also added
* updated text files as required by contributing
* ran make format

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Jim King <[email protected]>

Author: 3 people

AUTHORS.rst

@@ -48,6 +48,7 @@ Authors
 - Grzegorz Bialy
 - Guillermo Eijo (`guilleijo <https://github.com/guilleijo>`_)
 - Hamish Downer
+- Hans de Jong (`sult <https://github.com/sult>`_)
 - Hanyin Zhang
 - Hernan Esteves (`sevetseh28 <https://github.com/sevetseh28>`_)
 - Hielke Walinga (`hwalinga <https://github.com/hwalinga>`_)

CHANGES.rst

@@ -30,6 +30,7 @@ Full list of changes:
 - Dropped support for Python 3.6, which reached end-of-life on 2021-12-23 (gh-946).
 - Fix bug with ``history.diff_against`` with non-editable fields (gh-923)
 - Dropped support for Django 3.1 (gh-952)
+- RecordModels now support a ``no_db_index`` setting, to drop indices in historical models, default stays the same (gh-720)
 
 3.0.0 (2021-04-16)
 ------------------

docs/historical_model.rst

@@ -419,3 +419,31 @@ compatibility; it is more correct for a ``FileField`` to be converted to a
 
     SIMPLE_HISTORY_FILEFIELD_TO_CHARFIELD = True
 
+
+Drop Database Indices
+--------------------------------
+
+It is possible to use the parameter ``no_db_index`` to choose which fields
+that will not create a database index.
+
+For example, if you have the model:
+
+.. code-block:: python
+
+    class PollWithExcludeFields(models.Model):
+        question = models.CharField(max_length=200, db_index=True)
+
+
+
+And you don't want to create database index for ``question``, it is necessary to update the model to:
+
+.. code-block:: python
+
+    class PollWithExcludeFields(models.Model):
+        question = models.CharField(max_length=200, db_index=True)
+
+        history = HistoricalRecords(no_db_index=['question'])
+
+
+By default, django-simple-history keeps all indices. and even forces them on unique fields and relations.
+WARNING: This will drop performance on historical lookups

simple_history/models.py

@@ -80,6 +80,7 @@ def __init__(
         related_name=None,
         use_base_model_db=False,
         user_db_constraint=True,
+        no_db_index=list(),
         excluded_field_kwargs=None,
     ):
         self.user_set_verbose_name = verbose_name
@@ -101,6 +102,10 @@ def __init__(
         self.related_name = related_name
         self.use_base_model_db = use_base_model_db
 
+        if isinstance(no_db_index, str):
+            no_db_index = [no_db_index]
+        self.no_db_index = no_db_index
+
         if excluded_fields is None:
             excluded_fields = []
         self.excluded_fields = excluded_fields
@@ -305,6 +310,11 @@ def copy_fields(self, model):
                 field.name = old_field.name
             else:
                 transform_field(field)
+
+            # drop db index
+            if field.name in self.no_db_index:
+                field.db_index = False
+
             fields[field.name] = field
         return fields
 

simple_history/tests/models.py

@@ -770,3 +770,21 @@ class ModelWithExcludedManyToMany(models.Model):
     name = models.CharField(max_length=15, unique=True)
     other = models.ManyToManyField(ManyToManyModelOther)
     history = HistoricalRecords(excluded_fields=["other"])
+
+
+class ModelWithSingleNoDBIndexUnique(models.Model):
+    name = models.CharField(max_length=15, unique=True, db_index=True)
+    name_keeps_index = models.CharField(max_length=15, unique=True, db_index=True)
+    history = HistoricalRecords(no_db_index="name")
+
+
+class ModelWithMultipleNoDBIndex(models.Model):
+    name = models.CharField(max_length=15, db_index=True)
+    name_keeps_index = models.CharField(max_length=15, db_index=True)
+    fk = models.ForeignKey(
+        "Library", on_delete=models.CASCADE, null=True, related_name="+"
+    )
+    fk_keeps_index = models.ForeignKey(
+        "Library", on_delete=models.CASCADE, null=True, related_name="+"
+    )
+    history = HistoricalRecords(no_db_index=["name", "fk", "other"])

simple_history/tests/tests/test_models.py

@@ -70,6 +70,8 @@
     ModelWithFkToModelWithHistoryUsingBaseModelDb,
     ModelWithHistoryInDifferentDb,
     ModelWithHistoryUsingBaseModelDb,
+    ModelWithMultipleNoDBIndex,
+    ModelWithSingleNoDBIndexUnique,
     MultiOneToOne,
     MyOverrideModelNameRegisterMethod1,
     OverrideModelNameAsCallable,
@@ -1822,3 +1824,35 @@ def test_history_model_saved_in_separate_db_on_delete(self):
         self.assertEqual(
             0, ModelWithHistoryInDifferentDb.objects.using("other").count()
         )
+
+
+class ModelWithMultipleNoDBIndexTest(TestCase):
+    def setUp(self):
+        self.model = ModelWithMultipleNoDBIndex
+        self.history_model = self.model.history.model
+
+    def test_field_indices(self):
+        for field in ["name", "fk"]:
+            # dropped index
+            self.assertTrue(self.model._meta.get_field(field).db_index)
+            self.assertFalse(self.history_model._meta.get_field(field).db_index)
+
+            # keeps index
+            keeps_index = "%s_keeps_index" % field
+            self.assertTrue(self.model._meta.get_field(keeps_index).db_index)
+            self.assertTrue(self.history_model._meta.get_field(keeps_index).db_index)
+
+
+class ModelWithSingleNoDBIndexUniqueTest(TestCase):
+    def setUp(self):
+        self.model = ModelWithSingleNoDBIndexUnique
+        self.history_model = self.model.history.model
+
+    def test_unique_field_index(self):
+        # Ending up with deferred fields (dont know why), using work around
+        self.assertTrue(self.model._meta.get_field("name").db_index)
+        self.assertFalse(self.history_model._meta.get_field("name").db_index)
+
+        # keeps index
+        self.assertTrue(self.model._meta.get_field("name_keeps_index").db_index)
+        self.assertTrue(self.history_model._meta.get_field("name_keeps_index").db_index)