JOLT get only one value from an array inside an array

Question

I've been trying to figure out how to get the first value out of an array in my events array in this JSON.

I think I must do something with Cardinality but I can't quite figure it out so any help would be appreciated.

This is what my JSON looks like

{
  "rootid": "19718",
  "clloadm": "2021-06-01T22:40:02",
  "clload": "2021-06-01T21:21:39",
  "date": "2021-05-25T21:52:30",
  "events": [
    {
      "done": {
        "id": "e0",
        "value": "2021-05-29T08:08:19"
      },
      "id": "e0_event",
      "started": {
        "id": "e0",
        "value": "2021-05-29T08:08:19"
      },
      "status": "complete"
    },
    {
      "done": {
        "id": "e1",
        "value": "2021-05-27T02:20:25"
      },
      "id": "e1_event",
      "started": {
        "id": "e1",
        "value": "2021-05-27T02:20:25"
      },
      "status": "complete"
    },
    {
      "done": {
        "id": "e2",
        "value": "2021-05-29T08:08:19"
      },
      "id": "e2_event",
      "started": {
        "id": "e2",
        "value": "2021-05-29T08:08:19"
      },
      "status": "complete"
    },
    {
      "done": {
        "id": "e3",
        "value": "2021-05-29T08:08:19"
      },
      "id": "e3_event",
      "started": {
        "id": "e3",
        "value": "2021-05-29T08:08:19"
      },
      "status": "complete"
    },
    {
      "done": {
        "id": "e4",
        "value": "2021-05-29T08:08:19"
      },
      "id": "e4_event",
      "started": {
        "id": "e4",
        "value": "2021-05-29T08:08:19"
      },
      "status": "complete"
    }
  ],
  "ids": [
    {
      "id": "id",
      "source": "source",
      "value": "value"
    }
  ]
}

My Jolt Spec

[
  {
    "operation": "shift",
    "spec": {
      "*": "&",
      "events": {
        "*": {
          "*": {
            "@id": {
              "e0": { "@(2,value)": "&" },
              "e4": { "@(2,value)": "&" }
            }
          }
        }
      },
      "ids": {
        "*": {
          "@value": "@id"
        }
      }
    }
  }
]

The result I get:

{
  "rootid" : "19718",
  "clloadm" : "2021-06-01T22:40:02",
  "clload" : "2021-06-01T21:21:39",
  "date" : "2021-05-25T21:52:30",
  "e0" : [ "2021-05-29T08:08:19", "2021-05-29T08:08:19" ],
  "e4" : [ "2021-05-29T08:08:19", "2021-05-29T08:08:19" ],
  "id" : "value",
  "new_id" : "value"
}

I would like the result to be more like this where only the first value is selected:

{
  "rootid" : "19718",
  "clloadm" : "2021-06-01T22:40:02",
  "clload" : "2021-06-01T21:21:39",
  "date" : "2021-05-25T21:52:30",
  "e0" : "2021-05-29T08:08:19",
  "e4" : "2021-05-29T08:08:19",
  "id" : "value",
  "new_id" : "value"
}

Edit: I've tried adding the cardinality into my spec, but I can't seem to get the result I want.

[
  {
    "operation": "shift",
    "spec": {
      "*": "&",
      "events": {
        "*": {
          "*": {
            "@id": {
              "e0": { "@(2,value)": "&" },
              "e4": {
                "operation": "cardinality",
                "spec": {
                  "e4": "ONE"
                }
              }
            }
          }
        }
      },
      "ids": {
        "*": {
          "@value": "@id"
        }
      }
    }
  }
]

Barbaros Özhan Barbaros Özhan · Accepted Answer · 2021-07-22T17:03:54

Yes, you just can add a cardinality transformation such as

{
  "operation": "cardinality",
  "spec": {
    "*": "ONE"
  }
}

or optionally use e* wildcard just to restrict the result for the arrays with keys starting with the letter e such as

{
  "operation": "cardinality",
  "spec": {
    "e*": "ONE"
  }
}

Edit : just need to add to the current spec. So, you can use the following :

[
  {
    "operation": "shift",
    "spec": {
      "*": "&",
      "events": {
        "*": {
          "*": {
            "@id": {
              "e0": {
                "@(2,value)": "&"
              },
              "e4": {
                "@(2,value)": "&"
              }
            }
          }
        }
      },
      "ids": {
        "*": {
          "@value": "@id"
        }
      }
    }
  },
  {
    "operation": "cardinality",
    "spec": {
      "e*": "ONE"
    }
  }
]

JOLT get only one value from an array inside an array

1 Answers