Generate "src/main/resources/db/migration" structure for Flyway projects

[tedyoung]

Out-of-the-box, the ApplicationTests.contextLoads() test will fail with a generated project that uses Flyway because there's no default migration file.

Adding an empty V1__init.sql file into the resources/db/migration directory would make that test pass and be a nicer experience.

[snicoll]

The test and the app fails and this is not the only case where this happens.

We are usually trying to avoid any kind of scaffolding here and we generally favor clear exceptions (you have to do something) vs generating code to make things work and "hide" important information from you. We also absolutely don't want to be in a situation where we generate too much stuff and users have to manually remove what we've generated as we thought would be a convenience to them.

I am torn on this particular use case though, flagging for team attention.

[wilkinsona]

I think it's worth noting that, IIRC, this is only the case in recent versions of Flyway. Previously, it would silently do nothing if it didn't find any migrations to run. That leads me to believe that the Flyway team now think it's better to fail and guide the user towards creating a migration than to silently do nothing. I'm inclined to agree with them.

[snicoll]

Perhaps we could generate the src/main/resources/db/migration folder though?

[wilkinsona]

That sounds reasonable to me. On the Boot side, perhaps we should consider some failure analysis for the exception that Flyway throws as well?

[tedyoung]

I think that's a good way to go. I always have my training students run the contextLoads test after generation to make sure everything was imported, etc., correctly. When it failed, it wasn't immediately clear how to fix it as Flyway's docs don't mention an empty project -- but that's something they need to do if they're going to throw an exception.

[tedyoung]

So it looks like Boot is the one complaining as part of autoconfigure (see https://github.com/spring-projects/spring-boot/blob/2.1.x/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/flyway/FlywayAutoConfiguration.java#L191)

For adding Flyway to an existing Boot project that already has database schemas, etc., that check makes sense, but for a newly generated project, it's confusing ("how can I write a migration when I don't have any code yet?"). I feel like there needs to be better guidance, though I agree that generating an empty migration, which then has to be modified or thrown away, might not be best.