Flyway Java migration not supported in native images

[bclozel]

As discussed on gitter with @jnizet :

Hi team. I was just experimenting with native image support with a small application I have, and I think I found a missing piece in the native support. Flyway migrations are correctly detected and run... except the Java migrations. I get the following warning from Flyway at startup:

WARN 1 --- [ main] o.f.core.internal.command.DbMigrate : Schema "public" has a version (011) that is newer than the latest available migration (010) !

And the reason is that the migration 011, which has been run by a previous run of the application (in "non-native" mode), is a Java migration rather than a more traditional SQL migration (https://flywaydb.org/documentation/tutorials/java)

While we support the discovery of static sql migration files at runtime in a native image (using a custom resolver, org.springframework.boot.autoconfigure.flyway.NativeImageResourceProviderCustomizer) we are currently missing reflection metadata entries for the Java migration classes, since they are instantiated reflectively.

[mhalbritter]

I'm not 100% sure that it's enough to register hints for the migration classes. Flyway somehow needs to find them, and classpath scanning in native-image doesn't work like it does on the JVM. We might need to find them at AOT build time and then help flyway find them later in the native image.

[mhalbritter]

I've documented the limitation here: https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-with-GraalVM#flyway

[mhalbritter]

You can work around this issue by declaring a bean of type FlywayConfigurationCustomizer and register your Flyway Java migrations manually:

@Component
class JavaMigrationsFlywayCustomizer implements FlywayConfigurationCustomizer {

	@Override
	public void customize(FluentConfiguration configuration) {
		configuration.javaMigrations(new V1__create_table(), new ...);
	}

}

[wilkinsona]

I don't think we should tackle this one. There's a fairly straightforward workaround (that I've added to the existing Flyway section in the wiki) and I think any further improvements in this area should be made in Flyway itself.