Strategies for handling updates in existing JPA persistence classes

Hi All,

Good Afternoon.

We are doing a project in which we have planned to use JPA Persistence. We think that once the project goes live, there is a small chance that changes in the data model might be required.

My query is that what are the different strategies available to handle such a change. Particularly I have following questions:

1. With updated JPA classes, what are the best practices to incorporate them in the existing database schema?

2. With JPA, are there any best practices to, archive old data, update database schema, and again migrate the database to the new schema?

3. What are the various kinds of changes (broadly speaking) that will make such a migration impossible?

Thanks and Love to all
Ravi