Hibernate question hbm2ddl.auto possible values and what they do

Question

I really want to know more about the update, export and the values that could be given to 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 it attributes
• tables have been dropped
• values of a column has changed

In each case what is the best solution?

Answer 1

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.

Answer 2

I would use liquibase for updating your db. hibernate's schema update feature is really only o.k. for a developer while they are developing new features. In a production situation, the db upgrade needs to be handled more carefully.

Answer 3

Hi,
A while ago I wrote a detailed explanation on my blog, IMO it might help you. Take a look in here.
Eyal

Answer 4

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 at the end of the session.

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 5

I was in a great trouble about this. Your post helped me lot. Thanks