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• CC seems to be incomplete, over-promising interface
  • while claiming to be "the connection" to the data source it merely provides the conversion between different forms of the item (id → Vaadin Item → url fragment and back);
  • CC doesn't provide any child/parent relations API;
• part of CC's functionality becomes obsolete with Vaadin 8
  
  • Vaadin Items are no longer there, the corresponding CC methods can/should go too;
• It is hard to extend the CC interface. E.g. if we want to add API that provides support for item version look-up or support for item creation - we have to create the extending interface and then cast the CC to the extension;
• CC is not generic (partially cause it is not possible to inject generics with Guice);

Instead of single CC interface we can introduce a concept of a DataSourceSupport:

• it would be based on an arbitrary DS definition attached to app/sub-app/view
• it would manage so-called 'bundles' of utilities that provide various functionality realted to the data source.
  • once an app with JCR DS configured needs e.g. a Vaadin HierarchicalDataProvider, we can ask the DS support to give one. It looks up the bundle corresponding to JCR DS definition and sees if the bundle provides an HDataProvider.
  • Bundles are completely arbitrary, they may contain domain specific utlitites and components

Benefits

• Flexible and versatile provisioning of DS components (properysets, data providers, hierarchy look-ups, to-string converters etc)
  
  

Concerns

• Such solution adds a bit of magic - DSSupport and DS Bundles are yet two more layers of indirection, though still they typically should be concealed behind IoC - maybe that is not a big deal?
• It wouldn't be easy to provision generic DS components via Guice, the #newInstance(...) variant will work just fine.

Vaadin 8 brings in new concepts to the data binding

• no more Item abstraction → no more JcrNodeAdapter
• no more Container → no more JcrContainer

DataProvider

• Container concept replacement: interface for querying the data from a datasource
• Works with domain objects (e.g. JCR Nodes) instead of Items
• Stateless by design (one can implement caching manually though)
  
  

PropertySet

• Item concept replacement
• Unlike Item is more or less stateless component itself - only describes how to interact with the domain object to access [and modify] its properties via funtional primitives (lambdas), e.g. via bean getter/setter method references.

Benefits

• Simpler and slimmer way to connect to the datasources
• Less memory consumption (no additional abstractions over the domain objects)
• Easier to implement various providers (REST, ORM...)
• Supposedly better implementation hierarchical data providers

Concerns

• DataProvider still requires item indexing API
• Size query API still needs to be implemented (bummer for JCR list views)
• Observation of the DataProvider changes is still to be drafted!