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
There’s also the undocumented value of “none” to disable it entirely.
The configuration property is called
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.
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.
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.
Although it is quite an old post but as i did some research on the topic so thought of sharing it.
As per the documentation it can have four valid values:
create | update | validate | create-drop
Following is the explanation of the behaviour shown by these value:
- create :- create the schema, the data previously present (if there) in the schema is lost
- update:- update the schema with the given values.
- validate:- validate the schema. It makes no change in the DB.
- create-drop:- create the schema with destroying the data previously present(if there). It also drop the database schema when the SessionFactory is closed.
Following are the important points worth noting:
- In case of update, if schema is not present in the DB then the schema is created.
- In case of validate, if schema does not exists in DB, it is not created. Instead, it will throw an error:-
Table not found:<table name>
- In case of create-drop, schema is not dropped on closing the session. It drops only on closing the SessionFactory.
- In case if i give any value to this property(say abc, instead of above four values discussed above) or it is just left blank. It shows following behaviour:-If schema is not present in the DB:- It creates the schema-If schema is present in the DB:- update the schema.
hibernate.hbm2ddl.auto automatically validates and exports DDL to the schema when the sessionFactory is created.
By default, it does not perform any creation or modification automatically on DB. If the user sets one of the below values then it is doing DDL schema changes automatically.
- create – doing creating a schema
<entry key="hibernate.hbm2ddl.auto" value="create">
- update – updating existing schema
<entry key="hibernate.hbm2ddl.auto" value="update">
- validate – validate existing schema
<entry key="hibernate.hbm2ddl.auto" value="validate">
- create-drop – create and drop the schema automatically when a session is starts and ends
<entry key="hibernate.hbm2ddl.auto" value="create-drop">
If you don’t want to use Strings in your app and are looking for predefined constants have a look at
org.hibernate.cfg.AvailableSettings class included in the Hibernate JAR, where you’ll find a constant for all possible settings. In your case for example:
/** * Auto export/update schema using hbm2ddl tool. Valid values are <tt>update</tt>, * <tt>create</tt>, <tt>create-drop</tt> and <tt>validate</tt>. */ String HBM2DDL_AUTO = "hibernate.hbm2ddl.auto";
validate: validates the schema, no change happens to the database.
update: updates the schema with current execute query.
create: creates new schema every time, and destroys previous data.
create-drop: drops the schema when the application is stopped or SessionFactory is closed explicitly.
Hope you learned something from this post.
Follow Programming Articles for more!