When an application contains multiple DataSource beans, EntityManagerFactoryBuilder will default ddl-auto to a value that may only be appropriate for the primary DataSource

[randomComitter]

After updating Spring Boot from 3.3.5 to 3.4.3, the default ddl-auto create-drop will be applied to the non-embedded database if project has two databases, one of them is an embedded db and no explicit value is set for spring.jpa.hibernate.ddl-auto in application properties.
Is this a bug or an intended behavior?

The current documentation for Database Initialization mentions the following:

If an embedded database is identified and no schema manager (Flyway or Liquibase) has been detected, ddl-auto defaults to create-drop. In all other cases, it defaults to none.

which gives impression that create-drop will be applied by default only to the embedded database.
However, sometime between Spring Boot 3.3.5 and 3.4.3 a change was made so that default value create-drop for spring.jpa.hibernate.ddl-auto was applied to all data sources whether they were embedded or not (if at least one of them was embedded), which is dangerous behaviour and can lead to unexpected data loss in production databases.

[wilkinsona]

Please provide a minimal sample that reproduces the behavior you have described. There are too many unknowns at the moment in terms of how the two databases and the entity managers that depend on them are configured.

[randomComitter]

@wilkinsona thanks for your reply.

Sure, here's a minimal project that reproduces described behavior: https://github.com/randomComitter/dropcreate

[wilkinsona]

Thanks for the sample.

The change in behavior is due to this change. The ddl-auto setting (determined using the primary DataSource) is now applied to the auto-configured EntityManagerFactoryBuilder rather than only being applied to the auto-configured LocalContainerEntityManagerFactoryBean.

You're injecting the EntityManagerFactoryBuilder and using it to create both LocalContainerEntityManagerFactoryBeans in your app. As a result, they now have the same ddl-auto configuration as determined from the primary DataSource. You won't see the problem if you flip to ExternalDataSourceConfiguration defining the primary beans and qualify those defined by EmbeddedDataSourceConfiguration as the default ddl-auto will now by for an external DataSource.

I think the ideal here would be that configuring the DataSource on the builder results in the ddl-auto being updated if it hasn't already been explicitly configured. However, I'm not yet sure if that's possible.