[jira] [Commented] (NIFI-4149) Indicate if EL is evaluated against FFs or not

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/NIFI-4149?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16403550#comment-16403550 ] 

ASF GitHub Bot commented on NIFI-4149:
--------------------------------------

Github user pvillard31 commented on the issue:

    https://github.com/apache/nifi/pull/2205
  
    @joewitt @markap14 
    I finally found time to get back to this one. I updated every component to use the new method with the EL scope, I updated the mock framwork to fail in case scope is not correctly set, I updated the documentation, changed a bit the UI to add the scope in both the processor documentation and the properties tooltip.
    
    A bit like the recent change with the definition of dependencies in poms, this PR is quite impacting and possibly/probably conflicting with opened PRs. Let me know if you have feedbacks/comments.
    
    Note - @markap14, I didn't address your comment to document the variables made available in some processors like in RouteText. I can do it in this PR or in a follow-up JIRA. Just wanted to get the main work done asap, took me quite some time :)


> Indicate if EL is evaluated against FFs or not
> ----------------------------------------------
>
>                 Key: NIFI-4149
>                 URL: https://issues.apache.org/jira/browse/NIFI-4149
>             Project: Apache NiFi
>          Issue Type: Improvement
>          Components: Core Framework
>            Reporter: Pierre Villard
>            Assignee: Pierre Villard
>            Priority: Major
>
> With the addition of EL in a lot of places to improve SDLC and workflow staging, it becomes important to indicate to users if the expression language enabled on a property will be evaluated against the attributes of incoming flow files or if it will only be evaluated against various variable stores (env variables, variable registry, etc).
> Actually, the expression language (without evaluation against flow files) could be allowed on any property by default, and evaluation against flow files would be what is actually indicated in the UI as we are doing today. Adopting this approach could solve a lot of JIRA/PRs we are seeing to add EL on some specific properties (without evaluation against FFs).
> Having expression language to access external values could make sense on any property for any user. However evaluating the expression language against FFs is clearly a more complex challenge when it comes to session management and such.



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