java - working - hibernate.hbm2ddl.auto validate
Hibernate hbm2ddl.auto possible values and what they do? (9)
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">
I really want to know more about the update, export and the values that could be given to
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?
validate: It validates the schema and makes no changes to the DB.
Assume you have added a new column in the mapping file and perform the insert operation, it will throw an Exception "missing the XYZ column" because the existing schema is different than the object you are going to insert. If you alter the table by adding that new column manually then perform the Insert operation then it will definitely insert all columns along with the new column to the Table. Means it doesn't make any changes/alters the existing schema/table.
update: it alters the existing table in the database when you perform operation.
You can add or remove columns with this option of hbm2ddl.
But if you are going to add a new column that is 'NOT NULL' then it will ignore adding that particular column to the DB. Because the Table must be empty if you want to add a 'NOT NULL' column to the existing table.
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.
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.
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?
I dedicated a blog post for the most common Hibernate DDL generation strategies:
hibernate.hbm2ddl.auto="update"is convenient but less flexible if you plan on adding functions or executing some custom scripts.
- The most flexible approach is to use Flyway.
However, even if you use Flyway, you can still generate the initial migration script using hbm2ddl. In this article, you can see how you can combine the JPA Entity Model with jOOQ Table Model.
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.
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.
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.
validate: validate the schema, do not change happens to the database. update: update the schema with currently execute query. create: creates new schema every time, and destroy previous data. create-drop: drop the schema when the application is stopped or SessionFactory is closed explicitly.