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Thursday, May 4. 2006
Hibernate Annotations Schema Handling
With Hibernate's new EJB3 Annotation support, you can easily write classes, add annotations in code, and have Hibernate generate your database schemas for you without needing to manually build any xml config files or build your database schemas yourself. This is really bleeding edge though, so it has some issues. The Hibernate tools classes haven't caught up to the new feature set, for example, so when you try:
java -cp <classpaths> org.hibernate.tool.hbm2ddl.SchemaExport --config=hibernate.xml.cfg
To get the schema out so you can build your database, you get errors like:
org.hibernate.MappingException: An AnnotationConfiguration instance is required to use <blah>
Even when everything is properly setup and you have included the Hibernate Annotations jars in your classpath. Fortunately, there is a simple workaround.
java -cp <classpaths> org.hibernate.tool.hbm2ddl.SchemaExport --config=hibernate.xml.cfg
To get the schema out so you can build your database, you get errors like:
org.hibernate.MappingException: An AnnotationConfiguration instance is required to use <blah>
Even when everything is properly setup and you have included the Hibernate Annotations jars in your classpath. Fortunately, there is a simple workaround.
If you add this option to your hibernate.cfg.xml (or do a similar configuration with the other available options):
<!-- Drop and re-create the database schema on startup -->
<property name="hbm2ddl.auto">create</property>
This will create the database when the application is started.
Doing this would be very dangerous, obviously, on a production database. So I recommend creating a temporary database, then run your code to build a database on the temporary db. Then you can export the database with your db tools, verify the tables and sequences are set up the way you want and build any indexes you need, remove that line from your config file so the system won't nuke your production data, and setup the production database with this set of sql statements.
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I was getting this same error when using the HibernateToolTask with Ant. My solution was to rename the 'configuration' element to 'annotationconfiguration' and that's it.
In addition to change the element in hibernate.cfg.xml, need to change it in HibernateUtil.java
To further clarify what this posting was all about, the complaint here is that there is no easy way to dump the ddl of annotated classes from the command line. This bug was reported, but the hibernate team rejected it, their solution being to use a complicated ant task or write your own program as a wrapper. This defeats the whole point of having an easy class for dumping ddl from the command line.
The rejected bug:
http://opensource.atlassian.com/projects/hibernate/browse/HBX-732
The rejected bug:
http://opensource.atlassian.com/projects/hibernate/browse/HBX-732