[jboss-as7-dev] Default values in the model

Emanuel, Or chat yesterday about the downsides of storing default values in the in-memory management model got me thinking a bit. Downsides: 1) The in-memory model no longer represents the user configuration values; it also stores defaults. This is an issue when marshalling back to xml; you either have to make the xml verbose by writing back all the defaults, or you don't write back defaults and lose the fact the user included the value in the original. 2) Possible versioning issues in a domain where different hosts run different versions; i.e. if the version on the domain controller host stores and pushes to servers a default value that a server running an earlier version doesn't understand. This would really be a bug, since a change in a default value should spur an increment in the subsystem's schema and appropriate handling by the parser. But still, storing defaults increases the chances of this kind of bug cropping up. Possible solution: What's been requested previously is that management clients be able to see the default values, without having to go read the resource description metadata to find them. That request can be satisfied via the read-resource and read-attribute handlers. There is no need to store the default in the model; those handlers can read the resource description metadata to find the default if the model doesn't have a value stored. That will slow those handlers down a little bit since the description has to be generated and read, but those handlers aren't called as part of our internal operations (e.g. boot) so doing it that way won't slow down boot, deployment etc. An issue that doing it this way raises is a client calling read-resource or read-attribute doesn't know if the returned value is the actual user config or is a default. A solution to that is to have those operations accept a new parameter "defaults" which if false does not include the defaults. I'm not sure what the best default value for that "default" param would be. My instinct is "true". WDYT? -- Brian Stansberry Principal Software Engineer JBoss by Red Hat