Flatten Array using Jolt Transformation

June 26, 2022

This is input JSON which has array, which can contain one or more objects.
inside the object lang is array. It will always have one object which is fix. I want to flatten it.

[
  {
    "name": "James",
    "id": 1,
    "lang": [
      {
        "primary": "python",
        "secondary": "c++"
      }
    ]
  },
  {
    "name": "Kevin",
    "id": 2,
    "lang": [
      {
        "primary": "scala",
        "secondary": "java"
      }
    ]
  }
]

I want to flatten the JSON like this – expected output

[
  {
    "name": "James",
    "id": 1,
    "primary": "python",
    "secondary": "c++"
  },
  {
    "name": "Kevin",
    "id": 2,
    "primary": "scala",
    "secondary": "java"
  }
]

Im tryin to build specification like this but its not working

[
  {
    "operation": "shift",
    "spec": {
      "*": {
        "name": "[&1].name",
        "id": "[&1].id",
        "lang": {
          "*": {
            "primary": "lang\\[&2\\]\\.primary",
            "secondary": "lang\\[&2\\]\\.secondary"
          }
        }
      }
    }
  }
]

>Solution :

No need to escape for the square bracket characters
Increment from [&2] to [&3] as the value on the right hand
side(in order to traverse the colon following the innermost "*" )
Try to think symbolically(no need to repeat the literals, but use
ampersands to replicate them)

such as

[
  {
    "operation": "shift",
    "spec": {
      "*": {
        "*": "[&1].&", // the rest of the attributes(other than "lang" array)
        "lang": {
          "*": {
            "*": "[&3].&"
          }
        }
      }
    }
  }
]

the demo on the site http://jolt-demo.appspot.com/ is