Schema generation properties not well documented

[ghost]

Unfortunately my previous issue #11678 was closed as duplicate, though I don't think it is one.

In the issue I argued that the documentation is not entirely clear on which of several similar properties have precedence.

The referenced issue suggest other default values of certain properties in some contexts.

I would be glad if the documentation could be improved.

[snicoll]

@FelixRiemann you were referring to several issues into one and the problem of not enabling create-drop with Flyway/Liquibase has been addressed already (which means you don't have to set that ddl.auto either).

As for the documentation, it is not clear what you're asking really. So please clarify and we can see what can be improved in the documentation.

In the future, please comment on a declined issue rather than creating another one. We can always refine and reopen.

[ghost]

There are four properties I am interested in:

• (1) spring.jpa.generate-ddl (boolean)
• (2) spring.jpa.properties.javax.persistence.schema-generation.database.action (one of none, drop, create, drop-and-create)
• (3) spring.jpa.hibernate.ddl-auto (one of none, validate, update, create, create-drop)
• (4) spring.datasource.initialize (boolean)

From the documentation, the following is unclear to me:

1. Both (1) and (2) exist to enable/disable schema generation. I would like to know which of both has precedence.
2. Property (4) governs whether the schema should be generated from DML scripts. What happens if this is enabled together with one of (1) or (2)?
3. Then there is (3), which is similar to (2). What happens if they contradict each other?
4. What happens if (1) and (3) contradict each other (and here by contradict I mean any combination other than (none, none) and (true, create))?
5. If I do not set (3) specifically, will its default value override (1)? In Spring Boot 1.5.9 this is the case, as I pointed out in Schema generation properties not well documented #11678. But even if the default value of (3) will be none when Flyway/Liquibase is detected, as suggested in Default Hibernate auto-DDL to "none" with embedded database when Flyway or Liquibase is detected #9262, the question remains whether (3) overrides (1) if I do not use (3).

In the future, please comment on a declined issue rather than creating another one. We can always refine and reopen.

Will keep that in mind.

[m7stock]

What these questions have in common is that they mix different approaches. I think the documentation of their correlation would be quite complex and sometimes even beyond the control of Spring Boot itself:

Both (1) and (2) exist to enable/disable schema generation. I would like to know which of both has precedence.

spring.jpa.generate-ddl applies properties to the JPA implementation directly, i.e. hibernate.hbm2ddl.auto becomes "update" when spring.jpa.generate-ddl is true. Later, JPA 2.1 schema creation properties are evaluated by Hibernate and javax.persistence.schema-generation.database.action takes precedence over hibernate.hbm2ddl.auto unless it is unset or set to none.

Therefore, I referenced a commit that adds general notes to the documentation.

[wilkinsona]

Superseded by #15859.