Database Versioning with Liquibase

In my experience software developers and database people do not fit too well together. The database guys like to think of their database as a solid piece and dislike changing the schema. In an ideal world the schema is fixed for all time.

Software developers on the other hand tend to think about everything as a subject to change. This is even more true for agile teams embracing refactoring. Liquibase is a tool making database refactorings feasible and revertable. For the cost of only one additional jar-file you get a very flexible tool for migrating from one schema version to another.

Using Liquibase

  • You formulate the changes in XML, plain SQL or even as custom java migration classes. If you are careful and sometimes provide additional information your changes can be made rollbackable so that changing between schema revisions becomes a breeze.
  • To apply the changes you simply run the liquibase.jar as a standalone java application. You can specify tags to update or rollback to or the count of changesets to apply. This allows putting the database in an arbitrary state within changeset granularity.

Additional benefits

  • An important benefit of Liquibase is that you can easily put all your changesets under version control so that they are managed exactly the same as the rest of the application.
  • Liquibase stores the changelog directly in the database in a table called databasechangelog. This enables the developer and the application to check the schema revision of the database and thus find inkonsistent states much easier.

Conclusion
All of the above is especially useful when multiple installations or development/test databases with different verions of the software and therefore database have to be used at the same time. Tracking the changes to the database in the repository and having a small cross platform tool to apply them is priceless in many situations.

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