Referencing objects across VM boundaries

Whenever objects in an OO system need to be referenced outside their enclosing VM or VM session we have a problem. For instance, how to display a link to that specific object in the system in the text of an email message that it's being sent to an user? A different instance of the same problem is the scenario where a client application requests objects from a server application running in a different process (frequently in a different machine) and then submits the objects back after they were changed in some meaningful way by the user. A common solution to the first problem and a partial solution to the second one is to assign unique identifiers to every object that needs to be referenced across VM boundaries. A complete solution to the second one also requires some way to reconcile the state of the objects in the system after they have travelled back and forth. With the event system now exposed by db4o it is possible to start thinking of a reusable solution to the problems outlined above. The ... Read the rest of entry »

External Callbacks

Overview External Callbacks enable you to add Listeners to an ObjectContainer for the following db4o events Query Started Query Finished Creating (first time an object is about to be saved) Created (after the object is saved) Activating Activated Deactivating Deactivated Updating Updated Deleting Deleted All of the event types are defined in the EventRegistry interface, so keep an eye on that interface for any changes. Benefits Do not have to pollute your object model with persistence code With the old callbacks, you had to add methods to your objects like objectOnDelete() Multiple event handlers can be registered on particular events With the old callbacks, you could only have a single method on your objects C ... Read the rest of entry »