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Imagine you are developing a Java EE app using Hibernate and JBoss. You have a running server that has some important data on it. You release the next version of the app once in a while (1-2 weeks) and they have a bunch of changes in the persistence layer:
How do you effectively set up a system that updates the database schema and preserves the data? As far as I know (I may be mistaking), Hibernate doesn't perform alter column, drop/alter constraint.
Thank you, Artem B.
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If your database is created/updated automatically by some modeling tool, I think the best you way you should do is to understand those changes and write the "alter table" statements yourself and run it in your deployment.
LiquiBase is your best bet. It has a hibernate integration mode that uses Hibernate's hbm2ddl to compare your database and your hibernate mapping, but rather than updating the database automatically, it outputs a liquibase changelog file which can be inspected before actually running.
While more convenient, any tool that does a comparison of your database and your hibernate mappings is going to make mistakes. See http://www.liquibase.org/2007/06/the-problem-with-database-diffs.html for examples. With liquibase you build up a list of database changes as you develop in a format that can survive code with branches and merges.
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