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https://issues.apache.org/jira/browse/SLING-3886?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14112785#comment-14112785
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Stefan Seifert commented on SLING-3886:
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allowing to separate interface from implementation has in itself a virtue
benefiting testability/mockability and separating API from implementation in
context of one single application.
but you are right, unlike in OSGi it is not possible to have multiple
implementations of the same interface, or to be more precise the adaptTo API
provides no way to select between different implementations currently. but that
could be an extension in the future, either be enhancing the adaptTo API, or in
context of multitenancy support where the sling models implementation could
return different implementations for different tenants or configuration scopes.
but this would be a separate story, the multitenancy stuff is still in an early
stage of discussion.
> Sling Models: support adapters for models different from the implementation
> class
> ---------------------------------------------------------------------------------
>
> Key: SLING-3886
> URL: https://issues.apache.org/jira/browse/SLING-3886
> Project: Sling
> Issue Type: New Feature
> Components: Extensions
> Reporter: Stefan Seifert
> Labels: models
> Fix For: Sling Models Implementation 1.0.8, Sling Models API 1.0.4
>
> Attachments: 140827_SLING-3886_adapters_support.patch
>
>
> currently, as adapter (adaption target) only the implementation class itself
> that is annotated with the @Model annotation is supported (which can be
> either an interface or a class).
> if the model is not just a simple model but a class with more complex
> business logic the following scenario is required:
> * a "service" interface is defined
> * this service interface ist not directly mapped to injected values, but
> provides higher-level method
> * an implementation class with @Model annotation is implemented which gets
> the required values injectd internally, but implements the interface for
> outside access
> this is currently not possible with sling models.
> the attached patch extends the following features:
> * extends the @Model annotation with an optional "adapters" attribute
> * if defined, only the listed adapters are registered for the adapter
> factory, not the implementation class itself (unless it is listed the
> "adapters" attribute as well)
> * in the adapters attribute only the implementation class itself or
> interfaces that it implements or superclasses can be defined
> * with this the scenario above is perfectly possible
> * unit tests included which simulate the bundle add/remove usecases which is
> required to do the indirect implementation class mapping
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