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 <mattyb...@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.mcderm...@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. > > >
