JoltTransformJSON processor in NiFi(json without any parent tag)

Question

I need to transform a JSON data using the JoltTransformJSON inside Nifi, here's my spec which I am using for the transformation:

[{
"operation": "shift",
"spec": {
    "*": {
        "Header": {
            "readOn": "created_date_time",
            "fileName": "readFile"
        },
        "Data": {
            "id": "Id",
            "first_name": "First_Name",
            "last_name": "Last_Name",
        }
    }
}}]

My input data:

[{
"Header": {
    "readOn": "2017/04/18 10:55:05",
    "fileName": "sample1.csv",
    "recordNum": 1
},
"Data": {
    "last_name": "Martin",
    "id": 21,
    "first_name": "Clarence"
}
}, {
"Header": {
    "readOn": "2017/04/18 10:55:05",
    "fileName": "sample.csv",
    "recordNum": 2
},
"Data": {
    "last_name": "Graham",
    "id": 22,
    "first_name": "Walter"
}
}]

Output what I m getting:

{
"created_date_time": ["2017/04/18 10:55:05", "2017/04/18 10:55:05"],
"readFile": ["sample1.csv", "sample2.csv"],
"Id": [21, 22],
"First_Name": ["Clarence", "Walter"],
"Last_Name": ["Martin", "Graham"]
}

The required output:

[{
"recordNum": 1,
"Header": {
    "created_date_time": "2017/04/18 10:55:05",
    "readFile": "getusroi.csv"
},
"Data": {
    "Last_Name": "Martin",
    "Id": 21,
    "First_Name": "Clarence"
}
}, {
"recordNum": 2,
"Header": {
    "created_date_time": "2017/04/18 10:55:05",
    "readFile": "getusroi.csv"
},
"Data": {
    "Last_Name": "Graham",
    "Id": 22,
    "First_Name": "Walter"
}
}]

Question: Can someone guide me where all I need to change my jolt spec to achieve the desired transformed output.

Answer 1

The trick is to walk back up the tree until you get to the element in the array, then you can reference that index in the target. Try this spec:

[
  {
    "operation": "shift",
    "spec": {
      "*": {
        "Header": {
          "recordNum": "[&2].recordNum",
          "readOn": "[&2].&1.created_date_time",
          "fileName": "[&2].&1.readFile"
        },
        "Data": {
          "id": "[&2].&1.Id",
          "first_name": "[&2].&1.First_Name",
          "last_name": "[&2].&1.Last_Name"
        }
      }
    }
  }
]