Actually Cayenne allows you to easily implement a generic event
mechanism. IMO this is much more powerful than regular Java Beans
approach, although requires some understanding of how things work.
In "cayenne classic" (DataContext/DataObject) you can implement a
generic event mechanism in one place in a superclass that works
consistently for all objects. You do that by overriding methods in
DataObject interface (writeProperty). No need to put your code in the
individual setters. It is up to you how you fire the events (you can
fire two complimentary events on relationship change if you want).
Another way that works in both DataContext and CayenneContext and
will likely become a default way after 1.2, is overriding
ObjectContext.propertyChanged(..) method to fire the events. This
allows to track all events by context in addition to tracking events
of individual objects. IIRC there are limitations using this with
DataContext, but it should fully work in CayenneContext.
In other words tracking object changes is one of the hidden strengths
of Cayenne. I wish it wasn't so hidden, so if anyone volunteers to do
a tutorial or an example based on real experience, you'll be very
welcome.
Andrus
On Jun 19, 2006, at 12:12 PM, Tomi NA wrote:
I'm wrestling with this issue myself: I've extended the basic
templates so that events are fired on setter calls, but this practice
has the exact shortcomings you pointed out.
Is there a very good reason why cayenne objects don't fire events on a
lower level (circumventing this problem) out of the box?
Alternatively, if I expand my object code generation templates further
so that objectA.removeFrom(objectB) fires a property change event for
it's objectA.getBArray() as well as objectB.getToA() - will this
completely solve the problem?
