Regroup all elements of nested array of nested array into a single array-CodePudding

I have this collection :

{
  "_id": ObjectId("6045eec8f113547ddd3472d9"),
  "execution": {
    "_id": ObjectId("6045eec8f113547ddd3472d8"),
    "steps": [
      {
        "_id": ObjectId("6045eec8f113547ddd3472d7"),
        "actions": [
          {
            "_id": ObjectId("6045eec8f113547ddd3472d6"),
            "title": "action title"
          }
        ]
      }
    ]
  }
}

and i want to achieve this result:

{
  "_id": ObjectId("6045eec8f113547ddd3472d9"),
  "allActions": [
    {
      "_id": ObjectId("6045eec8f113547ddd3472d6"),
      "title": "action title"
    }
  ]
}

to clarify more, i want to add an array that groups together all "actions" under the "steps" array

db.getCollection("missions").aggregate([
    {
        $match: {
            _id: ObjectId("6045eec8f113547ddd3472d9")
        }
    },
    {
        $addFields: {
            "allActions": "$execution.steps"
        }
    }
])

Could someone help me complete the part of the code that will allow me to achieve the desired output?

CodePudding user response：

You may just use $reduce and $concatArrays to group all the entries in the actions array

db.missions.aggregate([
  {
    $match: {
      _id: ObjectId("6045eec8f113547ddd3472d9")
    }
  },
  {
    $addFields: {
      "allActions": {
        "$reduce": {
          "input": "$execution.steps.actions",
          "initialValue": [],
          "in": {
            "$concatArrays": [
              "$$value",
              "$$this"
            ]
          }
        }
      }
    }
  }
])

Here is the Mongo playground for your reference.