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From "Felix Meschberger (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FELIX-3377) Allow a component to update its own service properties
Date Sun, 06 May 2012 09:58:58 GMT

    [ https://issues.apache.org/jira/browse/FELIX-3377?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13269172#comment-13269172

Felix Meschberger commented on FELIX-3377:

> Also, I can't see any reason the bind/unbind and updated methods (and deactivate) shouldn't
be able
> to affect the service properties in the same way. 

My patch allows the "updated" method (I call it the modified method) to return service properties.

Allowing the deactivate method to return service properties makes no sense to me. A service
registered on behalf of a component is defined with default service registration properties.
Those properties may be changed upon component activation. But they should probably be reverted
to the original properties before component activation for symmetry reasons. I don't think
the deactivate method should be able to define yet another set of properties.

I am not sure, whether the bind and unbind methods should be able to affect the service registration
properties. Do you have concrete use cases in mind ?

In any case, I think my mechanism of defining a MethodResult class conveying the result is
more flexible that extending the ActivationParameter which is specific to activate style methods
(activate, deactivate, and modified).

> but I think that we need to distinguish between a method whose return type is Dictionary
but returns null

This distinction may be important for a modified object, right. My patch does not currently
support this, but this would be simple: The BaseMethod.invokeMethod currently checks for the
result of invoking the method. This could be extended to be multi-state:

    * If the method is void, return MethodResult.NONE (maybe rename this to MethodResult.VOID)
    * Else return a MethodResult instance with the actual result, which may in fact be null,
is returned

Consequently the callers (ImmediateComponentManager.createImplementationObject and ImmediateComponentManager.modify)
should be changed to account for this disctinction.
> Allow a component to update its own service properties
> ------------------------------------------------------
>                 Key: FELIX-3377
>                 URL: https://issues.apache.org/jira/browse/FELIX-3377
>             Project: Felix
>          Issue Type: Improvement
>          Components: Declarative Services (SCR)
>    Affects Versions:  scr-1.6.0
>            Reporter: David Jencks
>         Attachments: FELIX-3377-2.diff, FELIX-3377-3.diff, FELIX-3377-4.diff, FELIX-3377-returnDictionary.patch,
> If you just register a service in code, you can give the ServiceRegistration to the service
and it can update its service properties to reflect what it can discover about its environment.
 This proposes that services registered through DS should be able to do this too, by calling
an updateProperties(Dictionary) method on the ComponentContext.  (Since we'd need a spec update
to add the method to ComponentContext, I added a new interface that ComponentContextImpl implements).
> Right now a service could get Config Admin and modify the properties there, but then
(a) the update method is called even though the component itself initiated the changes and
(b) the new property values are persisted which is presumably not desired.
> According to the spec config admin properties override default property values specified
in the component xml.  I think that in order to reduce confusion, once a property has been
set through config admin it should not be possible to update it through this update method.
 This also makes implementing this idea easy.
> IIUC this idea does not make sense for component factories.
> This idea was originally suggested by Erin Schnabel in OSGI bug 2250.

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