Hibernate's hbm2ddl Tool
Hi again,
The Hibernate hbm2ddl is a tool allows us to create, update, and validate a database schema using Hibernate mappings configuration. The .hbm files are Hibernate mapping files, but since the schema export/validation is done using the the internal configuration Hibernate creates for the entities mapping, we can use still use hbm2ddl when working with JPA. As usual in here I write about the JPA environment, just remember that the hbm2ddl can also be invoked from command line or using Ant task.
Setup
To invoke Hibernates hbm2ddl during the creation of the entity manager factory set the 'hibernate.hbm2ddl.auto' property to one of
create
Hibernate will create the database when the entity manager factory is created (actually when Hibernate's SessionFactory is created by the entity manager factory). If a file named import.sql exists in the root of the class path ('/import.sql') Hibernate will execute the SQL statements read from the file after the creation of the database schema. It is important to remember that before Hibernate creates the schema it empties it (delete all tables, constraints, or any other database object that is going to be created in the process of building the schema).
create-drop
Same as 'create' but when the entity manager factory (which holds the SessionFactory) is explicitly closed the schema will be dropped.
update
Hibernate creates an update script trying to update the database structure to the current mapping. Does not read and invoke the SQL statements from import.sql. Useful, but we have to be careful, not all of the updates can be done performed ? for example adding a not null column to a table with existing data.
validate
Validates the existing schema with the current entities configuration. When using this mode Hibernate will not do any changes to the schema and will not use the import.sql file.
The Hibernate hbm2ddl is a tool allows us to create, update, and validate a database schema using Hibernate mappings configuration. The .hbm files are Hibernate mapping files, but since the schema export/validation is done using the the internal configuration Hibernate creates for the entities mapping, we can use still use hbm2ddl when working with JPA. As usual in here I write about the JPA environment, just remember that the hbm2ddl can also be invoked from command line or using Ant task.
Setup
To invoke Hibernates hbm2ddl during the creation of the entity manager factory set the 'hibernate.hbm2ddl.auto' property to one of
· create
· create-drop
· update
· validate
Here is an example:<persistence> <persistence-unit name="sampleContext" transaction-type="RESOURCE_LOCAL"> <provider>org.hibernate.ejb.HibernatePersistence</provider> <properties> <property name="hibernate.connection.driver_class" value="org.apache.derby.jdbc.ClientDriver"> <property name="hibernate.connection.username" value="app"> <property name="hibernate.connection.password" value="app"> <property name="hibernate.connection.url" value="jdbc:derby://localhost:1527/HibernateTestDB;create=true"> <property name="hibernate.hbm2ddl.auto" value="validate"> </properties> </persistence-unit> </persistence>
The Options and Their Meanings
create
Hibernate will create the database when the entity manager factory is created (actually when Hibernate's SessionFactory is created by the entity manager factory). If a file named import.sql exists in the root of the class path ('/import.sql') Hibernate will execute the SQL statements read from the file after the creation of the database schema. It is important to remember that before Hibernate creates the schema it empties it (delete all tables, constraints, or any other database object that is going to be created in the process of building the schema).create-drop
Same as 'create' but when the entity manager factory (which holds the SessionFactory) is explicitly closed the schema will be dropped. update
Hibernate creates an update script trying to update the database structure to the current mapping. Does not read and invoke the SQL statements from import.sql. Useful, but we have to be careful, not all of the updates can be done performed ? for example adding a not null column to a table with existing data.validate
Validates the existing schema with the current entities configuration. When using this mode Hibernate will not do any changes to the schema and will not use the import.sql file.Mode | Reads import.sql | Alters Database Structure | Comments |
update | No | Yes | |
create | Yes | Yes | Empties the database before creating it |
create-drop | Yes | Yes | Drops the database when the SessionFactory is closed |
validate | No | No |
Comments
keep them coming.ty
thanks again.
There might be a way to export the DDL commands but I am not familiar with any.
Eyal
Thanks,
Gurudutta
The default value is just not to do anything - just to leave the schema as is.
Eyal
It is still the only valuable information of hbm2ddl.auto after 4 years.
Stathis Alexopoulos
How do we go about dropping the column with hbm2ddl tool?
Boy, that is NOT the behavior I'm seeing. Not only is it still replacing my schema, it's replacing it with an OLD schema. Grrr.
Thanks for this post.
Worked for me.
I got a Hibernate Exception, showing …. “Wrong column type in . for column Created_by_User_ID. Found: bigint, expected: int”
A couple of questions:
1. Where does the “import.sql”, exist or gets created?
2. Is there a way to get a report of all the inconsistencies that exist as Unit test execution stops when it hits the first problem;
I have to correct it, execute UT again to get the next inconsistency.
Would prefer to get a full report, instead.
TIA !!
~g1