| # 20. Refactoring and "Schema Evolution" ## 20.1. Introduction By Refactoring, we mean anything that will change the shape of the class as it is stored on the disk. In the context of other databases (where the database structure is said to be a "Schema"), refactoring is also called Schema Evolution. ## 20.2. What db4objects does today automatically or easily Db4o automaticaly handles the most common refactoring or schema evolution changes for you. - Changing the interface or API to a class - Adding a field - Removing a field In addition, Db4o can rename classes and fields simply: - Db4o.configure().objectClass("package.class").rename("newPackage.newClass"); - Db4o.configure().objectClass("package.class").objectField("oldField").rename("newField"); If you modify a field's type, db4o will internally create a new field of the same name, but with the new type. The values of the old typed field will still be present, but be hidden. If you change the type back to the old type the old values will still be there. ## 20.3. What is not yet automated If you want to move a class to a new place in the inheritence hierarchy, you will need to follow the following procedure: - Create the new class in the proper location using a temporary name - Write manual code to create objects of the new class from the old ones - Delete the old objects - Run Defragment - Rename the temporary class name back to the correct name -- generated by Doctor courtesy of db4objects Inc.