Add support for DDL files in KPM

[pierre]

It would be nice if KPM could install the DDL files too. We probably need to add a flag, so upgrades don't clobber existing tables.

[sbrossie]

Yeah it would be nice ;-)

[pierre]

Some thoughts:

• Because Ruby plugins already rely on ActiveRecord (see here for example), we should use Rails migrations for these
• We don't have a migration solution today for Java code (Kill Bill or Java plugins). We could investigate https://flywaydb.org/, and if it's a fit, use it for both

KPM could then have a new verb to detect outdated DB schemata (and maybe run it by default post installation too) and output the SQL to run the migration(s) (ALTER statements and updates to migration versioning tables). This would be more useful in practice than simply having kpm run all migrations because:

1. In production, only DBAs with special access can effectively change tables structure
2. We don't want to force the DBA to use special tools (maven, ruby, ...) to apply the changes

[sbrossie]

I agree with the thoughts:

1. I think we want to provide the best tooling so the manual install/update becomes easy
2. We don't want any automatic magic

[pierre]

Proposal: 18f069e.

[pierre]

@bgandon, @beccagaspard: we've published a proposal on how database migrations would work with Kill Bill and its plugins: https://github.com/killbill/killbill-docs/blob/v3/userguide/tutorials/database_migrations.adoc.

Since you both expressed interest in such tooling, feel free to let us know if you have any feedback and/or if this would work in your organizations. Thanks!