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From neykov <...@git.apache.org>
Subject [GitHub] incubator-brooklyn pull request: Feature: transform state
Date Wed, 24 Sep 2014 12:59:42 GMT
Github user neykov commented on the pull request:

    https://github.com/apache/incubator-brooklyn/pull/177#issuecomment-56665694
  
    Completed the review. Very useful functionality. I like the YAML approach to defining
the transformers. 
    
    I'd like to put down in writing some thoughts, not directly related to this PR. 
      * There are use-cases where access to the whole collection of items is needed. A single
transformer could need multiple passes or a more complex strategy for updates. For example
creating, deleting items, splitting classes, transforms related to object IDs (references).
      * The person administering the brooklyn instance most certainly doesn't know enough
of the entity internals and changes to be able to write the transforms needed for updating
to a new version. He can see that there is a problem with rebinding and even check the error
message and pass it on. It is the entity creators' obligation and ability to create the transforms.
Would be great if we allow bundling the transforms along with the entities in the same deliverable.
This way the administrator could pass the problem to the entity developer who will create
a new version of the package and push it back to the brooklyn instance to resolve the rebinding
problem. For entities not distributed with brooklyn this is even more important.
      * If we bundle the transforms with the entities and don't have a person hand picking
them for each specific installation then we have the issues of ordering and which ones to
apply. When third party entities get involved then it becomes even more complex.
      * We have discussed a functionality which, as a part of CI, to test rebinding against
a real-world storage location for early warning. Not sure if this is a good idea, having a
step as part of the maven build which automatically serializes each new entity it finds and
during testing tries to rebind it.


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