id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
27286	Tests fail on MySQL when using multi-db and some DB is read-only due to supports_transactions() call	Jose M Herrero	Mariusz Felisiak	"I'm triying to implement a multi-db platform with one master and some read-replicas, I wanted to reflect this structure also in tests. When I run tests they try to write to read only databases although router is configured to not allow it.
To reproduce with nothing interfering I started a fresh project, these are the steps to reproduce:

1. Start a new Django 1.10.1 project with `django-admin startproject mysite` and cd into it `cd mysite`
2. Create a database router `mysite/dbrouter.py`
{{{
#!div style=""font-size: 80%""
Code highlighting:
  {{{#!python
class DbRouter(object):
    def db_for_read(self, model, **hints):
        return 'read_replica'

    def db_for_write(self, model, **hints):
        return 'default'

    def allow_relation(self, obj1, obj2, **hints):
        return True

    def allow_migrate(self, db, app_label, model_name=None, **hints):
        if db == 'read_replica':
            return False
        return True
   }}}
}}}

3. Edit `mysite.settings.py` with master and read databases and set the database router

{{{
#!div style=""font-size: 80%""
Code highlighting:
  {{{#!python
DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'mysite',
        'USER': 'myuser',
        'PASSWORD': 'mypassword',
        'HOST': '127.0.0.1',
        'PORT': '',
    },
    'read_replica': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'mysite',
        'USER': 'myuser_read',
        'PASSWORD': 'myreadpassword',
        'HOST': '127.0.0.1',
        'PORT': '',
    },
}
DATABASE_ROUTERS = ['mysite.dbrouter.DbRouter']
}}}
}}}

4. Create `mysite/tests.py`
{{{
#!div style=""font-size: 80%""
Code highlighting:
  {{{#!python
from django.test import TestCase

class SurveyFormTest(TestCase):
    def test_sample(self):
        print 'hello'
}}}
}}}
5. Execute the tests and bang! `python manage.py test mysite`

{{{
Creating test database for alias 'default'...
E
======================================================================
ERROR: setUpClass (mysite.tests.SurveyFormTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File ""/home/chemary/workspace/myvirtualenv/local/lib/python2.7/site-packages/django/test/testcases.py"", line 1009, in setUpClass
    if not connections_support_transactions():
  File ""/home/chemary/workspace/myvirtualenv/local/lib/python2.7/site-packages/django/test/testcases.py"", line 974, in connections_support_transactions
    for conn in connections.all())
  File ""/home/chemary/workspace/myvirtualenv/local/lib/python2.7/site-packages/django/test/testcases.py"", line 974, in <genexpr>
    for conn in connections.all())
  File ""/home/chemary/workspace/myvirtualenv/local/lib/python2.7/site-packages/django/utils/functional.py"", line 35, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File ""/home/chemary/workspace/myvirtualenv/local/lib/python2.7/site-packages/django/db/backends/base/features.py"", line 235, in supports_transactions
    cursor.execute('CREATE TABLE ROLLBACK_TEST (X INT)')
  File ""/home/chemary/workspace/myvirtualenv/local/lib/python2.7/site-packages/django/db/backends/utils.py"", line 64, in execute
    return self.cursor.execute(sql, params)
  File ""/home/chemary/workspace/myvirtualenv/local/lib/python2.7/site-packages/django/db/utils.py"", line 94, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File ""/home/chemary/workspace/myvirtualenv/local/lib/python2.7/site-packages/django/db/backends/utils.py"", line 62, in execute
    return self.cursor.execute(sql)
  File ""/home/chemary/workspace/myvirtualenv/local/lib/python2.7/site-packages/django/db/backends/mysql/base.py"", line 112, in execute
    return self.cursor.execute(query, args)
  File ""/home/chemary/workspace/myvirtualenv/local/lib/python2.7/site-packages/MySQLdb/cursors.py"", line 205, in execute
    self.errorhandler(self, exc, value)
  File ""/home/chemary/workspace/myvirtualenv/local/lib/python2.7/site-packages/MySQLdb/connections.py"", line 36, in defaulterrorhandler
    raise errorclass, errorvalue
OperationalError: (1142, ""CREATE command denied to user 'myuser_read'@'localhost' for table 'ROLLBACK_TEST'"")

----------------------------------------------------------------------
Ran 0 tests in 0.026s

FAILED (errors=1)
Destroying test database for alias 'default'...
}}}
"	Bug	closed	Testing framework	1.10	Normal	duplicate	multi-db dbrouter		Unreviewed	0	0	0	0	0	0