How to transform data using Jolt spec in nifi

I want this data to be transformed in a given way using the jolt spec of Nifi.

Conditions are if studentId and loc_id are the same then we will combine their info and will pass the rest as it is. There are empty fields as well "".

Data

[
  {
    "studentId": "2222",
    "loc_id": "L1",
    "topId": "Lotus",
    "SubID1": "A1",
    "SubID2": "B1"
  },
  {
    "studentId": "2222",
    "loc_id": "L1",
    "topId": "tulip",
    "SubID1": "A2",
    "SubID2": ""
  },
  {
    "studentId": "3333",
    "loc_id": "L3",
    "topId": "Rose",
    "SubID1": "A3",
    "SubID2": ""
  },
  {
    "studentId": "4444",
    "loc_id": "L3",
    "topId": "Rose",
    "SubID1": "A5",
    "SubID2": "B7"
  }
]

Data after jolt spec: First two data have same studentId and loc_id so we have combined their info and rest two have passed as it is with an addition of visit list

[
  {
    "studentId": "2222",
    "loc_id": "L1",
    "VisitList": [
      {
        "topId": "Lotus",
        "SubID1": "A1",
        "SubID2": "B1"
      },
      {
        "topId": "tulip",
        "SubID1": "A2",
        "SubID2": ""
      }
    ]
  },
  {
    "studentId": "3333",
    "loc_id": "L1",
    "VisitList": [
      {
        "topId": "Rose",
        "SubID1": "A3",
        "SubID2": ""
      }
    ]
  },
  {
    "providerId": "4444",
    "specillity": "L3",
    "VisitList": [
      {
        "topId": "Rose",
        "SubID1": "A5",
        "SubID2": "B7"
      }
    ]
  }
]

Solution

You can use this spec:

[
  {
    "operation": "shift",
    "spec": {
      "*": {
        "@": "@(1,studentId).@(1,loc_id)"
      }
    }
  },
  {
    "operation": "cardinality",
    "spec": {
      "*": {
        "*": "MANY"
      }
    }
  },
  {
    "operation": "shift",
    "spec": {
      "*": {
        "*": {
          "*": {
            "studentId": "[#4].&",
            "loc_id": "[#4].&",
            "topId|SubID*": "[#4].VisitList[&1].&"
          }
        }
      }
    }
  },
  {
    "operation": "cardinality",
    "spec": {
      "*": {
        "studentId": "ONE",
        "loc_id": "ONE"
      }
    }
  }
]

1 - shift: You should create a unique root for every object. In this case, we create it by combining 2 values like this: @(1,studentId).@(1,loc_id).

2 - cardinality: change every object that has 1 object to an array. We should do this to prepare our input for the next shift operation.

3 - shift: create your desired output.

4 - cardinality: change studentId and loc_id to a string in all objects.