Unable to connect to Google Cloud SQL from development server using SQLAlchemy

Question

I\'ve been unsuccessful at connecting to Google Cloud SQL using SQLAlchemy 0.7.9 from my development workstation (in hopes to generate the schema using create_all()). I can

Answer 1

It turns out the mysql+gaerdbms:/// driver in SQLAlchemy was only setup to use the rdbms_apiproxy DBAPI, which can only be used when accessing Google Cloud SQL from a Google App Engine instance. I submitted a ticket to SQLAlchemy to update the driver to use the OAuth-based rdbms_googleapi when not on Google App Engine, just like the Django driver provided in the App Engine SDK. rdbms_googleapi is also the DBAPI that google_sql.py uses (remote sql console).

The updated dialect is expected to be part of 0.7.10 and 0.8.0 releases, but until they are available, you can do the following:

---

1 - Copy the updated dialect in the ticket to a file (ex. gaerdbms_dialect.py)

from sqlalchemy.dialects.mysql.mysqldb import MySQLDialect_mysqldb
from sqlalchemy.pool import NullPool
import re

"""Support for Google Cloud SQL on Google App Engine

Connecting
-----------

Connect string format::

    mysql+gaerdbms:///<dbname>?instance=<project:instance>


  # Example:
  create_engine('mysql+gaerdbms:///mydb?instance=myproject:instance1')
"""


class MySQLDialect_gaerdbms(MySQLDialect_mysqldb):

    @classmethod
    def dbapi(cls):
        from google.appengine.api import apiproxy_stub_map

        if apiproxy_stub_map.apiproxy.GetStub('rdbms'):
            from google.storage.speckle.python.api import rdbms_apiproxy
            return rdbms_apiproxy
        else:
            from google.storage.speckle.python.api import rdbms_googleapi
            return rdbms_googleapi

    @classmethod
    def get_pool_class(cls, url):
        # Cloud SQL connections die at any moment
        return NullPool

    def create_connect_args(self, url):
        opts = url.translate_connect_args()
        opts['dsn'] = ''  # unused but required to pass to rdbms.connect()
        opts['instance'] = url.query['instance']
        return [], opts

    def _extract_error_code(self, exception):
        match = re.compile(r"^(\d+):").match(str(exception))
        code = match.group(1)
        if code:
            return int(code)

dialect = MySQLDialect_gaerdbms

---

2 - Register the custom dialect (you can override the existing schema)

from sqlalchemy.dialects import registry
registry.register("mysql.gaerdbms", "application.database.gaerdbms_dialect", "MySQLDialect_gaerdbms")

Note: 0.8 allows a dialect to be registered within the current process (as shown above). If you are running an older version of SQLAlchemy, I recommend upgrading to 0.8+ or you'll need to create a separate install for the dialect as outlined here.

---

3 - Update your create_engine('...') url as the project and instance are now provided as part of the query string of the URL

mysql+gaerdbms:///<dbname>?instance=<project:instance>

for example:

create_engine('mysql+gaerdbms:///mydb?instance=myproject:instance1')

Answer 2

I think I have a working sample script as follows. Can you try a similar thing and let me know how it goes?

However(and you might be already aware of it), if your goal is to create the schema on Google Cloud SQL instance, maybe you can create the schema against a local mysql server, dump it with mysqldump, and then import the schema to Google Cloud SQL. Using local mysql server is very convenient for development anyway.

from sqlalchemy import create_engine
from google.storage.speckle.python.api import rdbms as dbi_driver
from google.storage.speckle.python.api import rdbms_googleapi

INSTANCE = 'YOURPROJECT:YOURINSTANCE'
DATABASE = 'YOURDATABASE'

def get_connection():       
    return rdbms_googleapi.connect('', instance=INSTANCE, database=DATABASE)

def main():
    engine = create_engine(
        'mysql:///YOURPROJECT:YOURINSTANCE/YOURDATABASE',
        module=dbi_driver,
        creator=get_connection,
    )
    print engine.execute('SELECT 1').scalar()

if __name__ == '__main__':
    main()