Can SQLAlchemy be used with Google Cloud SQL?
Yes,
If you find any bugs in SA+Cloud SQL, please let me know. I wrote the dialect code that was integrated into SQLAlchemy. There's a bit of silly business about how Cloud SQL bubbles up exceptions, so there might be some loose ends there.
For those who prefer PyMySQL over MySQLdb (which is suggested in the accepted answer), the SQLAlchemy connection strings are:
For Production
mysql+pymysql://<USER>:<PASSWORD>@/<DATABASE_NAME>?unix_socket=/cloudsql/<PUT-SQL-INSTANCE-CONNECTION-NAME-HERE>
Please make sure to
Add the SQL instance to your
app.yaml:beta_settings: cloud_sql_instances: <PUT-SQL-INSTANCE-CONNECTION-NAME-HERE>Enable the SQL Admin API as it seems to be necessary:
https://console.developers.google.com/apis/api/sqladmin.googleapis.com/overview
For Local Development
mysql+pymysql://<USER>:<PASSWORD>@localhost:3306/<DATABASE_NAME>
given that you started the Cloud SQL Proxy with:
cloud_sql_proxy -instances=<PUT-SQL-INSTANCE-CONNECTION-NAME-HERE>=tcp:3306
it is doable, though I haven't used Flask at all so I'm not sure about establishing the connection through that. I got it working through Pyramid and submitted a patch to SQLAlchemy (possibly to the wrong repo) here:
https://bitbucket.org/sqlalchemy/sqlalchemy/pull-request/2/added-a-dialect-for-google-app-engines
That has since been replaced and accepted into SQLAlchemy as
http://www.sqlalchemy.org/trac/ticket/2484
I don't think it's made it way to a release though.
There are some issues with Google SQL throwing different exceptions so we had issues with things like deploying a database automatically. You also need to disable connection pooling using NullPool as mentioned in the second patch.
We've since moved to using the datastore through NDB so I haven't followed the progess of these fixes for a while..
Update
Google Cloud SQL now supports direct access, so the MySQLdb dialect can now be used. The recommended connection via the mysql dialect is using the URL format:
mysql+mysqldb://root@/<dbname>?unix_socket=/cloudsql/<projectid>:<instancename>
mysql+gaerdbms has been deprecated in SQLAlchemy since version 1.0
I'm leaving the original answer below in case others still find it helpful.
For those who visit this question later (and don't want to read through all the comments), SQLAlchemy now supports Google Cloud SQL as of version 0.7.8 using the connection string / dialect (see: docs):
mysql+gaerdbms:///<dbname>
E.g.:
create_engine('mysql+gaerdbms:///mydb', connect_args={"instance":"myinstance"})
I have proposed an update to the mysql+gaerdmbs:// dialect to support both of Google Cloud SQL APIs (rdbms_apiproxy and rdbms_googleapi) for connecting to Cloud SQL from a non-Google App Engine production instance (ex. your development workstation). The change will also modify the connection string slightly by including the project and instance as part of the string, and not require being passed separately via connect_args.
E.g.
mysql+gaerdbms:///<dbname>?instance=<project:instance>
This will also make it easier to use Cloud SQL with Flask-SQLAlchemy or other extension where you don't explicitly make the create_engine() call.
If you are having trouble connecting to Google Cloud SQL from your development workstation, you might want to take a look at my answer here - https://stackoverflow.com/a/14287158/191902.