Doesn't work with MariaDB

[dismine]

Hi.

I must thank you for this amazing project! But it seems doesn't work with MariaDB. I tried with several versions: 5.5, 10.1, 10.3 and 10.4. Always the same result.

 Traceback (most recent call last):
   File "manage.py", line 23, in <module>
     execute_from_command_line(sys.argv)
   File "/opt/env/lib/python3.7/site-packages/django/core/management/__init__.py", line 381, in execute_from_command_line
     utility.execute()
   File "/opt/env/lib/python3.7/site-packages/django/core/management/__init__.py", line 375, in execute
     self.fetch_command(subcommand).run_from_argv(self.argv)
   File "/opt/env/lib/python3.7/site-packages/django/core/management/base.py", line 323, in run_from_argv
     self.execute(*args, **cmd_options)
   File "/opt/env/lib/python3.7/site-packages/django/core/management/base.py", line 364, in execute
     output = self.handle(*args, **options)
   File "/code/apps/test/management/commands/wait_for_database.py", line 91, in handle
     wait_for_database(**options)
   File "/code/apps/test/management/commands/wait_for_database.py", line 31, in wait_for_database
     connection.cursor().execute('SELECT')
   File "/opt/env/lib/python3.7/site-packages/django/db/backends/utils.py", line 67, in execute
     return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
   File "/opt/env/lib/python3.7/site-packages/django/db/backends/utils.py", line 76, in _execute_with_wrappers
     return executor(sql, params, many, context)
   File "/opt/env/lib/python3.7/site-packages/django/db/backends/utils.py", line 84, in _execute
     return self.cursor.execute(sql, params)
   File "/opt/env/lib/python3.7/site-packages/django/db/utils.py", line 89, in __exit__
     raise dj_exc_value.with_traceback(traceback) from exc_value
   File "/opt/env/lib/python3.7/site-packages/django/db/backends/utils.py", line 82, in _execute
     return self.cursor.execute(sql)
   File "/opt/env/lib/python3.7/site-packages/django/db/backends/mysql/base.py", line 71, in execute
     return self.cursor.execute(query, args)
   File "/opt/env/lib/python3.7/site-packages/MySQLdb/cursors.py", line 209, in execute
     res = self._query(query)
   File "/opt/env/lib/python3.7/site-packages/MySQLdb/cursors.py", line 315, in _query
     db.query(q)
   File "/opt/env/lib/python3.7/site-packages/MySQLdb/connections.py", line 231, in query
     _mysql.connection.query(self, query)
 django.db.utils.ProgrammingError: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 1")

Note. I have moved your command inside my project to be able to fix it. So, don't look at the path. Code is absolutely the same.

It seems like connection.cursor().execute('SELECT') doesn't wotk for MariaDB. But connection.cursor().execute('SELECT 1') does. What do you think?

[bittner]

Thank you for your feedback, and thanks for using django-probes in the first place! 🥇

Would you want to try placing a pull request for the change?

I would suggest to start with extending the test setup in a way that it covers more databases. Currently, only Postgres is tested against, which is apparently not enough. 😟

[dismine]

Hi.

Would you want to try placing a pull request for the change?

How do you propose to add a database-specific code?

[bittner]

The idea of this package is to be database independent. Ideally, we only add tests that prove that currently the code only works for Postgres and fails for MariaDB. Then we adapt the code to make it work for both database engines. Same for other engines, in future.

• To run tests against specific database engines we need to override the DATABASE settings using what pytest-django provides. This will allow us to write a simple test that you run once against Postgres and once again against MariaDB.
• You will need to add the mysqlclient package to the unit test dependencies in tox.ini.

Do you think you can do this?

[dismine]

We could try, it would be interesting. But I ask about a different thing. How to run a raw SQL depend on backend?

[bittner]

How to run a raw SQL depend on backend?

You make this dependent on your Django settings. Set the appropriate backend in your settings, then the SQL query will run against that specific DBMS.

[dismine]

No, i know this.

I am talking about this piece of code:

connection.cursor().execute('SELECT')

How to say?

if "MariaDB":
    connection.cursor().execute('SELECT 1')
elif "Postgres":
    connection.cursor().execute('SELECT')
else:
    raise Exception("Not supported backend.) #  Just as an example

[dismine]

I just realized that I could try to read settings and compare.

>>> from django.conf import settings
>>> settings.DATABASES['default']['ENGINE']
'django.db.backends.sqlite3' or 'django.db.backends.postgresql_psycopg2'

But quick search showed another way:

>>> from django.db import connection
>>> connection.vendor
'postgresql' or 'sqlite'

[dismine]

On StackOverflow, I have found a list with all ping queries. We could try to use it for extending a list of supported backends.

[bittner]

Wow, this is very helpful, cool! 🥇

So, we can use the appropriate ping query for the chosen database engine. That is one reason more to add additional tests for the different supported database engines. 👍

Side note:

What is also not yet supported is multiple databases. I have created a separate ticket (#4) for that.

[bittner]

This should work now with version 1.3.0 released last week. 🚀

Thanks for your valuable input! 🥇