https://community.cloudera.com/t5/Support-Questions/Unable-to-return-a-scalar-value-for-the-expression-from-NIFI/m-p/213677#M175601 <P>I'm using nifi to process json using Apache NIFI. </P><P>This is the input json:</P><P>{"key": "C919", "cells": [["year","2017",1497999002676770]]}</P><P>I'm using the following jsonpath expression: </P><P>$.cells[?(@[0]=='year')][1]</P><P>And in evaluatejsonpath processor, I got the following error:</P><P> EvaluateJsonPath[id=015c1006-dd8a-1d92-5eb2-9ed9822065f8] Unable to return a scalar value for the expression $['cells'][?][1] for FlowFile 69572. Evaluated value was [1999]. Transferring to failure.</P><P>But the return value is a scalar value here, It is 1999. And if I change the json expression to $.cells[?(@[0]=='year')][1][0]. It not allowed and throws error. </P><PRE>EvaluateJsonPath[id=015c1006-dd8a-1d92-5eb2-9ed9822065f8] EvaluateJsonPath[id=015c1006-dd8a-1d92-5eb2-9ed9822065f8] failed to process session due to com.jayway.jsonpath.InvalidPathException: Filter: [0] can only be applied to arrays. Current context is: 1999: com.jayway.jsonpath.InvalidPathException: Filter: [0] can only be applied to arrays. Current context is: 1999</PRE><P>Is it a bug in NIFI?</P> Wed, 21 Jun 2017 21:57:24 GMT jinxuanwu2013 2017-06-21T21:57:24Z https://community.cloudera.com/t5/Support-Questions/Unable-to-return-a-scalar-value-for-the-expression-from-NIFI/m-p/213677#M175601 <P>I'm using nifi to process json using Apache NIFI. </P><P>This is the input json:</P><P>{"key": "C919", "cells": [["year","2017",1497999002676770]]}</P><P>I'm using the following jsonpath expression: </P><P>$.cells[?(@[0]=='year')][1]</P><P>And in evaluatejsonpath processor, I got the following error:</P><P> EvaluateJsonPath[id=015c1006-dd8a-1d92-5eb2-9ed9822065f8] Unable to return a scalar value for the expression $['cells'][?][1] for FlowFile 69572. Evaluated value was [1999]. Transferring to failure.</P><P>But the return value is a scalar value here, It is 1999. And if I change the json expression to $.cells[?(@[0]=='year')][1][0]. It not allowed and throws error. </P><PRE>EvaluateJsonPath[id=015c1006-dd8a-1d92-5eb2-9ed9822065f8] EvaluateJsonPath[id=015c1006-dd8a-1d92-5eb2-9ed9822065f8] failed to process session due to com.jayway.jsonpath.InvalidPathException: Filter: [0] can only be applied to arrays. Current context is: 1999: com.jayway.jsonpath.InvalidPathException: Filter: [0] can only be applied to arrays. Current context is: 1999</PRE><P>Is it a bug in NIFI?</P> Wed, 21 Jun 2017 21:57:24 GMT https://community.cloudera.com/t5/Support-Questions/Unable-to-return-a-scalar-value-for-the-expression-from-NIFI/m-p/213677#M175601 jinxuanwu2013 2017-06-21T21:57:24Z https://community.cloudera.com/t5/Support-Questions/Unable-to-return-a-scalar-value-for-the-expression-from-NIFI/m-p/213678#M175602 <P>The answer in <A target="_blank" href="https://stackoverflow.com/questions/23608050/getting-a-single-value-from-a-json-object-using-jsonpath">this StackOverflow post</A> refers to documentation saying an array will be returned; this appears to be happening after the JSONPath is evaluated (which is why appending a [0] does not work). The post also implies the answer: in NiFi, you can choose "json" as the Return Type and "flowfile-attribute" as the Destination in EvaluateJsonPath (let's say your dynamic property has key "my.attr" and a value of your JSONPath expression above), then follow that processor with an UpdateAttribute processor, setting "my.attr" to the following:</P><PRE>${my.attr:jsonPath('$[0]')}</PRE><P>This will overwrite the original "my.attr" value by hoisting the value out of the array. If you need that value back in the content, you can follow this with a ReplaceText processor to replace the Entire Text with the value of "my.attr".</P> Wed, 21 Jun 2017 23:33:22 GMT https://community.cloudera.com/t5/Support-Questions/Unable-to-return-a-scalar-value-for-the-expression-from-NIFI/m-p/213678#M175602 mburgess 2017-06-21T23:33:22Z