how to replace empty string with null in nested json?

[#1]

Hi guys! I have json like that:

{
"id" : "20",
"user" : {
"name" : "John",
"date" : ""
}
}

I transform this date to Long using nifi langugage ${date:isEmpty():ifElse('',${date:toDate('yyyy-MM-dd HH:mm:ss'):toNumber()})} and after this i do in jolttrasformation something like

[
{
"operation": "shift",
"spec": {
"idTransakcji" : "id",
"date": "user.date",
}
},
{
"operation": "modify-overwrite-beta",
"spec": {
"user": {
"date": "=toLong(@(1,date))"
}
}
}

]

 and it works. But I have problem beacause when I have emptyString in this date i need to transfer it in null(not null in String) and i dont know how to do it using JoltTransformation or something else  so as not to lose what I already have and have null only when there is an empty string.

[#2]

Hi @MWM ,

replacing empty string with null is kind of tricky thing with jolt. Unfortunately there is no direct way that I know of but hopefully my comments will make it easy for you to understand. 

Based on your spec I assume you have the following input:

{
  "idTransakcji": "123",
  "date": "",
  "name": "sam"
}

The jolt spec would be like this ( comments start with //):

[
  {
    "operation": "shift",
    "spec": {
      "idTransakcji": "id",
      "date": {
        // Parse date value 
        // if its empty string ""
        "": {
          //remove the date from the output    	
          "": "user.date"
        },
        //For any values other than ""
        "*": {
          //assign the actual value ($) to user.date
          "$": "user.date"
        }
      },
      // Assign other fields like name under user
      "*": "user.&"
    }
  },
  {
    "operation": "modify-overwrite-beta",
    "spec": {
      "user": {
        // if the date is found it means that we
        // should have a value, therefore convert to long
        "date": "=toLong(@(1,date))"
      }
    }
  },
  {
    "operation": "default",
    "spec": {
      "user": {
        // if the date is not found then set to null
        // default transformation only works when 
        // the key doesnt exist.
        "date": null
      }
    }
  }
]

You can try the spec here : https://jolt-demo.appspot.com/#inception

If that helps please accept solution.

Thanks

[#3 · Accepted solution]

ExecuteGroovyScript alternative with this input

{
  "idTransakcji": "123",
  "date": "",
  "name": "sam"
}

import groovy.json.JsonOutput
import groovy.json.JsonSlurper
import java.nio.charset.StandardCharsets

JsonSlurper jsonSlurper = new JsonSlurper()
JsonOutput jsonOutput = new JsonOutput()

FlowFile flowFile = session.get()
if(!flowFile) return

flowFile = session.write(flowFile, { inputStream, outputStream -> 
                                        Map data = jsonSlurper.parse(inputStream)
                                        data = [
                                            "id": data.idTransakcji,
                                            "user": [
                                                "date": data.date?.isNumber() ? Long.parseLong(data.date) : null,
                                                "name": data.name
                                            ]
                                        ]
                                        outputStream.write(jsonOutput.toJson(data).getBytes(StandardCharsets.UTF_8))
                                  } as StreamCallback)
session.transfer(flowFile, REL_SUCCESS)

[#4]

Hi @SAMSAL your solution is workink, thank you so much!