From 83677faf860f1a25acd667131275307abaa23fc4 Mon Sep 17 00:00:00 2001
From: Nick Pope <nick.pope@flightdataservices.com>
Date: Wed, 19 Dec 2018 23:01:44 +0000
Subject: [PATCH] Fixed #30056 -- Added SQLite support for StdDev and Variance
functions.
---
django/db/backends/base/features.py | 12 +-----------
django/db/backends/sqlite3/base.py | 13 +++++++++++++
django/db/backends/sqlite3/features.py | 21 ---------------------
docs/ref/models/querysets.txt | 16 ++++------------
docs/releases/2.2.txt | 3 +++
tests/aggregation_regress/tests.py | 1 -
tests/backends/tests.py | 1 -
7 files changed, 21 insertions(+), 46 deletions(-)
diff --git a/django/db/backends/base/features.py b/django/db/backends/base/features.py
index 9787901b07..7a71c76bd3 100644
--- a/django/db/backends/base/features.py
+++ b/django/db/backends/base/features.py
@@ -1,5 +1,4 @@
-from django.db.models.aggregates import StdDev
-from django.db.utils import NotSupportedError, ProgrammingError
+from django.db.utils import ProgrammingError
from django.utils.functional import cached_property
@@ -298,12 +297,3 @@ class BaseDatabaseFeatures:
count, = cursor.fetchone()
cursor.execute('DROP TABLE ROLLBACK_TEST')
return count == 0
-
- @cached_property
- def supports_stddev(self):
- """Confirm support for STDDEV and related stats functions."""
- try:
- self.connection.ops.check_expression_support(StdDev(1))
- except NotSupportedError:
- return False
- return True
diff --git a/django/db/backends/sqlite3/base.py b/django/db/backends/sqlite3/base.py
index 1c39fb4add..5b1c80d27c 100644
--- a/django/db/backends/sqlite3/base.py
+++ b/django/db/backends/sqlite3/base.py
@@ -7,6 +7,7 @@ import functools
import math
import operator
import re
+import statistics
import warnings
from itertools import chain
from sqlite3 import dbapi2 as Database
@@ -49,6 +50,14 @@ def none_guard(func):
return wrapper
+def list_aggregate(function):
+ """
+ Return an aggregate class that accumulates values in a list and applies
+ the provided function to the data.
+ """
+ return type('ListAggregate', (list,), {'finalize': function, 'step': list.append})
+
+
Database.register_converter("bool", b'1'.__eq__)
Database.register_converter("time", decoder(parse_time))
Database.register_converter("datetime", decoder(parse_datetime))
@@ -210,6 +219,10 @@ class DatabaseWrapper(BaseDatabaseWrapper):
conn.create_function('SIN', 1, none_guard(math.sin))
conn.create_function('SQRT', 1, none_guard(math.sqrt))
conn.create_function('TAN', 1, none_guard(math.tan))
+ conn.create_aggregate('STDDEV_POP', 1, list_aggregate(statistics.pstdev))
+ conn.create_aggregate('STDDEV_SAMP', 1, list_aggregate(statistics.stdev))
+ conn.create_aggregate('VAR_POP', 1, list_aggregate(statistics.pvariance))
+ conn.create_aggregate('VAR_SAMP', 1, list_aggregate(statistics.variance))
conn.execute('PRAGMA foreign_keys = ON')
return conn
diff --git a/django/db/backends/sqlite3/features.py b/django/db/backends/sqlite3/features.py
index d76a1275f5..c57b8e1934 100644
--- a/django/db/backends/sqlite3/features.py
+++ b/django/db/backends/sqlite3/features.py
@@ -1,8 +1,6 @@
import sys
-from django.db import utils
from django.db.backends.base.features import BaseDatabaseFeatures
-from django.utils.functional import cached_property
from .base import Database
@@ -41,22 +39,3 @@ class DatabaseFeatures(BaseDatabaseFeatures):
# reasonably performant way.
supports_pragma_foreign_key_check = Database.sqlite_version_info >= (3, 20, 0)
can_defer_constraint_checks = supports_pragma_foreign_key_check
-
- @cached_property
- def supports_stddev(self):
- """
- Confirm support for STDDEV and related stats functions.
-
- SQLite supports STDDEV as an extension package; so
- connection.ops.check_expression_support() can't unilaterally
- rule out support for STDDEV. Manually check whether the call works.
- """
- with self.connection.cursor() as cursor:
- cursor.execute('CREATE TABLE STDDEV_TEST (X INT)')
- try:
- cursor.execute('SELECT STDDEV(*) FROM STDDEV_TEST')
- has_support = True
- except utils.DatabaseError:
- has_support = False
- cursor.execute('DROP TABLE STDDEV_TEST')
- return has_support
diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt
index 81a82fe7b6..9dd661e6a7 100644
--- a/docs/ref/models/querysets.txt
+++ b/docs/ref/models/querysets.txt
@@ -3400,12 +3400,9 @@ by the aggregate.
By default, ``StdDev`` returns the population standard deviation. However,
if ``sample=True``, the return value will be the sample standard deviation.
- .. admonition:: SQLite
+ .. versionchanged:: 2.2
- SQLite doesn't provide ``StdDev`` out of the box. An implementation
- is available as an extension module for SQLite. Consult the `SQLite
- documentation`_ for instructions on obtaining and installing this
- extension.
+ SQLite support was added.
``Sum``
~~~~~~~
@@ -3434,14 +3431,9 @@ by the aggregate.
By default, ``Variance`` returns the population variance. However,
if ``sample=True``, the return value will be the sample variance.
- .. admonition:: SQLite
+ .. versionchanged:: 2.2
- SQLite doesn't provide ``Variance`` out of the box. An implementation
- is available as an extension module for SQLite. Consult the `SQLite
- documentation`_ for instructions on obtaining and installing this
- extension.
-
-.. _SQLite documentation: https://www.sqlite.org/contrib
+ SQLite support was added.
Query-related tools
===================
diff --git a/docs/releases/2.2.txt b/docs/releases/2.2.txt
index f2e822f5a5..f731562640 100644
--- a/docs/releases/2.2.txt
+++ b/docs/releases/2.2.txt
@@ -235,6 +235,9 @@ Models
``Model.delete()``. This improves the performance of autocommit by reducing
the number of database round trips.
+* Added SQLite support for the :class:`~django.db.models.StdDev` and
+ :class:`~django.db.models.Variance` functions.
+
Requests and Responses
~~~~~~~~~~~~~~~~~~~~~~
diff --git a/tests/aggregation_regress/tests.py b/tests/aggregation_regress/tests.py
index 893b22ae69..29b32c4987 100644
--- a/tests/aggregation_regress/tests.py
+++ b/tests/aggregation_regress/tests.py
@@ -1116,7 +1116,6 @@ class AggregationTests(TestCase):
lambda b: (b.name, b.authorCount)
)
- @skipUnlessDBFeature('supports_stddev')
def test_stddev(self):
self.assertEqual(
Book.objects.aggregate(StdDev('pages')),
diff --git a/tests/backends/tests.py b/tests/backends/tests.py
index ee6bee3a02..d1b89950c0 100644
--- a/tests/backends/tests.py
+++ b/tests/backends/tests.py
@@ -340,7 +340,6 @@ class BackendTestCase(TransactionTestCase):
def test_cached_db_features(self):
self.assertIn(connection.features.supports_transactions, (True, False))
- self.assertIn(connection.features.supports_stddev, (True, False))
self.assertIn(connection.features.can_introspect_foreign_keys, (True, False))
def test_duplicate_table_error(self):