Add decorators and tests

.travis.yml

@@ -0,0 +1,7 @@
+language: python
+python:
+  - 3.8
+  - 3.6
+  - 2.7
+install: pip install tox-travis
+script: tox

readonly/cursor.py

@@ -105,8 +105,8 @@ def _last_executed(self):
 
 
 class PatchedCursorWrapper(utils.CursorWrapper):
-    def __init__(self, cursor, db):
-        self.cursor = ReadOnlyCursorWrapper(cursor, db)
+    def __init__(self, cursor, db,read_only=None):
+        self.cursor = ReadOnlyCursorWrapper(cursor, db, read_only=read_only)
         self.db = db
 
 

readonly/decorators.py

@@ -0,0 +1,49 @@
+from contextlib import contextmanager
+
+from django.db.backends import utils
+
+from readonly.cursor import (
+    PatchedCursorWrapper,
+    PatchedCursorDebugWrapper,
+)
+
+_orig_CursorWrapper = utils.CursorWrapper
+_orig_CursorDebugWrapper = utils.CursorDebugWrapper
+
+
+class ForcedPatchedCursorWrapper(PatchedCursorWrapper):
+    def __init__(self, cursor, db):
+        super(ForcedPatchedCursorWrapper, self).__init__(cursor, db, read_only=True)
+
+
+class ForcedPatchedCursorDebugWrapper(PatchedCursorDebugWrapper):
+    def __init__(self, cursor, db):
+        super(ForcedPatchedCursorDebugWrapper, self).__init__(
+            cursor, db, read_only=True
+        )
+
+
+@contextmanager
+def readonly():
+    old_CursorWrapper = utils.CursorWrapper
+    old_CursorDebugWrapper = utils.CursorDebugWrapper
+    utils.CursorWrapper = ForcedPatchedCursorWrapper
+    utils.CursorDebugWrapper = ForcedPatchedCursorDebugWrapper
+    try:
+        yield
+    finally:
+        utils.CursorWrapper = old_CursorWrapper
+        utils.CursorDebugWrapper = old_CursorDebugWrapper
+
+
+@contextmanager
+def write_enabled():
+    old_CursorWrapper = utils.CursorWrapper
+    old_CursorDebugWrapper = utils.CursorDebugWrapper
+    utils.CursorWrapper = _orig_CursorWrapper
+    utils.CursorDebugWrapper = _orig_CursorDebugWrapper
+    try:
+        yield
+    finally:
+        utils.CursorWrapper = old_CursorWrapper
+        utils.CursorDebugWrapper = old_CursorDebugWrapper

tests/models.py

@@ -0,0 +1,5 @@
+from django.db import models
+
+
+class Widget(models.Model):
+    name = models.CharField(max_length=100)

tests/settings.py

@@ -2,18 +2,18 @@
 
 DB_READ_ONLY_MIDDLEWARE_MESSAGE = False
 SITE_READ_ONLY = False
-DB_READ_ONLY_DATABASES = False
+DB_READ_ONLY_DATABASES = []
 
-DATABASE_ENGINE = "sqlite3"
-
-# Uncomment below to run tests with mysql
-# DATABASE_ENGINE = "django.db.backends.mysql"
-# DATABASE_NAME = "readonly_test"
-# DATABASE_USER = "readonly_test"
-# DATABASE_HOST = "/var/mysql/mysql.sock"
+DATABASES = {
+    "default": {
+        "ENGINE": "django.db.backends.sqlite3",
+        "NAME": ":memory:",
+    },
+}
 
 INSTALLED_APPS = [
     "readonly",
+    "tests",
 ]
 
 MIDDLEWARE = [

tests/test_context_manager.py

@@ -0,0 +1,88 @@
+from django.db import transaction
+from django.db.transaction import TransactionManagementError
+
+from django.test import TestCase
+
+from readonly.decorators import readonly, write_enabled
+from readonly.exceptions import DatabaseWriteDenied
+
+from tests.models import Widget
+
+
+class ContextManagerTestCase(TestCase):
+    def _create_obj(self):
+        with transaction.atomic():
+            obj = Widget.objects.create()
+            obj.save()
+
+    def test_normal(self):
+        Widget.objects.count()
+        obj = Widget.objects.create()
+        obj.save()
+
+    def test_readonly_transaction(self):
+        before = Widget.objects.count()
+
+        with readonly():
+            with self.assertRaises(DatabaseWriteDenied):
+                with transaction.atomic():
+                    obj = Widget.objects.create()
+                    obj.save()
+
+        after = Widget.objects.count()
+        assert after == before
+
+        obj = Widget.objects.create()
+        obj.save()
+
+        after = Widget.objects.count()
+        assert after == before + 1
+
+    def test_readonly(self):
+        Widget.objects.count()
+
+        with readonly():
+            with self.assertRaises(DatabaseWriteDenied):
+                obj = Widget.objects.create()
+                obj.save()
+
+        # TODO: Automatic cancellation of the transaction would simplify
+        # developer use of readonly & DatabaseWriteDenied with foreign code
+        with self.assertRaises(TransactionManagementError):
+            Widget.objects.count()
+
+    def test_nested_readonly_disabled(self):
+        with readonly():
+            with self.assertRaises(DatabaseWriteDenied):
+                self._create_obj()
+            with readonly():
+                with self.assertRaises(DatabaseWriteDenied):
+                    self._create_obj()
+                with readonly():
+                    with self.assertRaises(DatabaseWriteDenied):
+                        self._create_obj()
+
+        Widget.objects.create()
+
+    def test_readonly_enabled(self):
+        with readonly():
+            with write_enabled():
+                self._create_obj()
+
+    def test_nested_readonly_enabled(self):
+        with readonly():
+            with readonly():
+                with write_enabled():
+                    with readonly():
+                        with write_enabled():
+                            with readonly():
+                                with self.assertRaises(DatabaseWriteDenied):
+                                    self._create_obj()
+
+                with self.assertRaises(DatabaseWriteDenied):
+                    self._create_obj()
+
+            with self.assertRaises(DatabaseWriteDenied):
+                self._create_obj()
+
+        self._create_obj()

tox.ini

@@ -0,0 +1,18 @@
+[tox]
+envlist = py27-django{18,19,110,111}, py{36,37,38}-django{111,20,21,22,30,31}
+skip_missing_interpreters = True
+
+[testenv]
+commands = python -m django test {posargs}
+setenv =
+  DJANGO_SETTINGS_MODULE = tests.settings
+deps =
+    django18: Django>=1.8,<1.9
+    django19: Django>=1.9,<1.10
+    django110: Django>=1.10,<1.11
+    django111: Django>=1.11,<1.12
+    django20: Django>=2.0,<2.1
+    django21: Django>=2.1,<2.2
+    django22: Django>=2.2,<2.3
+    django30: Django>=3.0,<3.1
+    django31: Django>=3.1,<3.2