MySQL as Backend with Druid as datasource

[lony25]

When using mysql as URI scheme in caravel_config.py, everything works fine.
I could add druid cluster. When I try to refresh druid metadata, it throws following error:

sqlalchemy.exc.InvalidRequestError: This Session's transaction has been rolled back due to a previous exception during flush. To begin a new transaction with this Session, first issue Session.rollback(). Original exception was: (_mysql_exceptions.IntegrityError) (1452, 'Cannot add or update a child row: a foreign key constraint fails (caravel.columns, CONSTRAINT columns_ibfk_1 FOREIGN KEY (column_name) REFERENCES datasources (datasource_name))')

On debugging, I figured out that while calling sync_to_db, DruidDatasource is trying to modify DruidColumn which I understand is not allowed.

Could some one help me if I am doing something wrong or is it a valid issue.

OS: Ubuntu 14.04
Druid: 0.9
Caravel: 0.9

Steps to reproduce.

1. Change URI scheme to mysql as instructed in tutorial. Follow tutorial.
2. Add Druid cluster.
3. Do Druid Refresh Metadata.

[x4base]

Should be related to #466

[kkalyan]

I ran into same issue, temporary workaround is to remove foreign key

alter table columns drop foreign key columns_ibfk_1;

[xrmx]

Closing as duplicate of #466