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copied!<p>First, db4o handles the 'simple' <a href="http://developer.db4o.com/Documentation/Reference/db4o-7.12/java/reference/html/reference/implementation_strategies/refactoring_and_schema_evolution/automatic_refactoring.html" rel="noreferrer">scenarios like adding or removing a field automatically</a>. When you adding the field, all existing object have the default value stored. When you remove a field, the data of existing object is still in the database and you can still access it. Renaming field etc are <a href="http://developer.db4o.com/Documentation/Reference/db4o-7.12/java/reference/html/reference/implementation_strategies/refactoring_and_schema_evolution/refactoring_api.html" rel="noreferrer">special 'refactoring'-calls</a>.</p> <p>Now your scenario you would do something like this:</p> <ol> <li>Remove the field 'full_name', add the new fields 'first_name' and 'second_name'</li> <li>Iterate over all 'Address'-objects</li> <li>Access the old field via the 'StoredClass'-API</li> <li>Split, change, update etc the value. Set the new values on the new field and store the object.</li> </ol> <p>Let's assume we have a 'Address'-class. The 'full_name' field has been removed. Now we wan't to copy it to the 'firstname' and 'surname'. Then it could go like this (Java):</p> <pre><code> ObjectSet<Address> addresses = db.query(Address.class); StoredField metaInfoOfField = db.ext().storedClass(Address.class).storedField("full_name", String.class); for (Address address : addresses) { String fullName = (String)metaInfoOfField.get(address); String[] splitName = fullName.split(" "); address.setFirstname(splitName[0]); address.setSurname(splitName[1]); db.store(address); } </code></pre> <p>As you suggested, you would write migration-code for each version-bump. It a field isn't part of your class anymore, you have to access it with 'StoredField'-API like above. </p> <p>You can get a list of all 'stored' classes with <code>ObjectContainer.ext().storedClasses()</code>. With <code>StoredClass.getStoredFields()</code> you can get a list of all store fields, no mather is the field doesn't exist anymore in your class. If a class doesn't exist anymore, you can still get the objects and access it via 'GenericObject'-class. </p> <p><strong>Update: For complexer scenarios where a database needs to migrated over multiple-version-steps.</strong></p> <p>For example it in the version v3 the address-object looks completely different. So the 'migration-script' for v1 to v2 hasn't got the fields anymore it requires (firstname and surename in my example). I think there are multiple possibilities for handling this.</p> <ol> <li>(Assuming Java for this idea. Certainly there's an equivalent in .NET). You could make the migration-step a <a href="http://groovy.codehaus.org/" rel="noreferrer">Groovy-script</a>. So each that each script does not interfere with another. Then you define 'classes' the needed classes for the migration there. So each migration has its own migration-classes. With <a href="http://developer.db4o.com/Documentation/Reference/db4o-7.12/java/reference/html/reference/implementation_strategies/aliases.html" rel="noreferrer">aliases</a> you would bind your groovy-migration-classes to the actual java-classes. </li> <li>Creating refactoring-classes for complex scenarios. Also bind this classes with <a href="http://developer.db4o.com/Documentation/Reference/db4o-7.12/java/reference/html/reference/implementation_strategies/aliases.html" rel="noreferrer">aliases</a>.</li> </ol>

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