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From Aldrin Piri <aldrinp...@gmail.com>
Subject Re: NiFi-1660
Date Tue, 22 Mar 2016 16:51:54 GMT
Chris,

Awesome that you are ready to dive in and get this fixed up.  The
functionality is certainly one that would be helpful.
I do find myself a bit torn on whether the inclusion of this as EL is
preferred instead of the extension of EvaluateJsonPath as suggested
in NIFI-1567 [1].  Are there use cases that would not be fulfilled via
enhancements to the existing processor that I might be overlooking?

Thanks!

[1] https://issues.apache.org/jira/browse/NIFI-1567

On Tue, Mar 22, 2016 at 12:45 PM, Matt Burgess <mattyb149@gmail.com> wrote:

> Chris,
>
> Great to hear! For the following steps, I'm assuming it will be a
> one-argument function called "jsonPath" that takes a String containing a
> JSON Path expression to be evaluated on the "subject" of the function. So I
> am picturing it used like:
>
> ${ my.json.attribute:jsonPath("$.path.to.my.data") }
>
> To add such a function to EL, you'll likely want to do something like the
> following:
>
> 1) Add a token for the function name to the Lexer:
>
> https://github.com/apache/nifi/blob/master/nifi-commons/nifi-expression-language/src/main/antlr3/org/apache/nifi/attribute/expression/language/antlr/AttributeExpressionLexer.g#L120
>
> 2) Add the token to the oneArgString rule:
>
> https://github.com/apache/nifi/blob/master/nifi-commons/nifi-expression-language/src/main/antlr3/org/apache/nifi/attribute/expression/language/antlr/AttributeExpressionParser.g#L77
>
> 3) Add a JsonPathEvaluator class (or whatever its called) to the functions
> package:
>
> https://github.com/apache/nifi/tree/master/nifi-commons/nifi-expression-language/src/main/java/org/apache/nifi/attribute/expression/language/evaluation/functions
>
> 4) Add a case to Query.buildFunctionEvaluator() to create and use a new
> JsonPathEvaluator:
>
> https://github.com/apache/nifi/blob/master/nifi-commons/nifi-expression-language/src/main/java/org/apache/nifi/attribute/expression/language/Query.java#L1061
>
> 5) Add unit test(s) to TestQuery to test your function:
>
> https://github.com/apache/nifi/blob/master/nifi-commons/nifi-expression-language/src/test/java/org/apache/nifi/attribute/expression/language/TestQuery.java
>
> Also whatever dependencies you bring in (Jayway, e.g.) will need to be
> added to the EL module's POM:
>
> https://github.com/apache/nifi/blob/master/nifi-commons/nifi-expression-language/pom.xml
> .
> If a parent POM has declared a version already (such as the NiFi parent POM
> declaring jayway 2.0.0 at present), you may want to keep that unless you
> need to override for some reason.
>
> Looking forward to your contribution, please let me/us know if you run into
> any trouble or have any questions.
>
> Cheers,
> Matt
>
>
> On Tue, Mar 22, 2016 at 10:59 AM, McDermott, Chris Kevin (MSDU -
> STaTS/StorefrontRemote) <chris.mcdermott@hpe.com> wrote:
>
> > Hi folks,
> >
> > I’m a newbie NiFi user but long time Java developer.  I’ve entered a Jira
> > issue to extend the expression language to add a function to evaluate a
> > Json path against the subject.  Looking at the code I feel this is very
> > doable, and I am up for task so I’m planning on tackling it.  I’ve read
> the
> > developers guide, etc.  Please, any advice and direction is most welcome.
> >
> > Thanks,
> >
> > Chris McDermott.
> >
>

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