What are the possible values of the Hibernate hbm2ddl.auto configuration and what do they do – Dev

The best answers to the question “What are the possible values of the Hibernate hbm2ddl.auto configuration and what do they do” in the category Dev.

QUESTION:

I really want to know more about the update, export and the values that could be given to hibernate.hbm2ddl.auto
I need to know when to use the update and when not? And what is the alternative?

These are changes that could happen over DB:

  • new tables
  • new columns in old tables
  • columns deleted
  • data type of a column changed
  • a type of a column changed its attributes
  • tables dropped
  • values of a column changed

In each case what is the best solution?

ANSWER:

There’s also the undocumented value of “none” to disable it entirely.

ANSWER:

From the community documentation:

hibernate.hbm2ddl.auto Automatically validates or exports schema DDL to the database when the SessionFactory is created. With create-drop, the database schema will be dropped when the SessionFactory is closed explicitly.

e.g. validate | update | create | create-drop

So the list of possible options are,

  • validate: validate the schema, makes no changes to the database.
  • update: update the schema.
  • create: creates the schema, destroying previous data.
  • create-drop: drop the schema when the SessionFactory is closed explicitly, typically when the application is stopped.
  • none: does nothing with the schema, makes no changes to the database

These options seem intended to be developers tools and not to facilitate any production level databases, you may want to have a look at the following question; Hibernate: hbm2ddl.auto=update in production?

ANSWER:

First, the possible values for the hbm2ddl configuration property are the following ones:

  • none – No action is performed. The schema will not be generated.
  • create-only – The database schema will be generated.
  • drop – The database schema will be dropped.
  • create – The database schema will be dropped and created afterward.
  • create-drop – The database schema will be dropped and created afterward. Upon closing the SessionFactory, the database schema will be dropped.
  • validate – The database schema will be validated using the entity mappings.
  • update – The database schema will be updated by comparing the existing database schema with the entity mappings.

The hibernate.hbm2ddl.auto="update" is convenient but less flexible if you plan on adding functions or executing some custom scripts.

So, The most flexible approach is to use Flyway.

However, even if you use Flyway, you can still generate the initial migration script using hbm2ddl.

ANSWER:

The configuration property is called hibernate.hbm2ddl.auto

In our development environment we set hibernate.hbm2ddl.auto=create-drop to drop and create a clean database each time we deploy, so that our database is in a known state.

In theory, you can set hibernate.hbm2ddl.auto=update to update your database with changes to your model, but I would not trust that on a production database. An earlier version of the documentation said that this was experimental, at least; I do not know the current status.

Therefore, for our production database, do not set hibernate.hbm2ddl.auto – the default is to make no database changes. Instead, we manually create an SQL DDL update script that applies changes from one version to the next.