Mongo Project by referencing external Dictionary

Question

I have a collection in MongoDB:

[
  {
    "uid": "a1"
  },
  {
    "uid": "a2"
  }
]

and a dictionary in my JS code

let dict = { "a1": "ref1", "a1": "ref2" };

I want to do an aggregate that will somehow join the two.

let k = ;

this.model.aggregate([
  {
    $match: {
      uid: { $in: Object.keys(dict) }
    }
  },
  {
    $project: {
      ref: // here is where I want to add the equivalent reference
    }
  }
])

The expected output would be something like this:

[{uid: "a1", ref: "ref1"}, {uid: "a2", ref: "ref2}]

Is there a way to get the reference from the dict into the $project?

Answer 1

I don't know if there is an easier way to do it, but here's how I achieved it:

db.collection.aggregate([
  {
    $match: {
      uid: {
        $in: [
          "a1",
          "a2"
        ]
      }
    }
  },
  {
    "$project": {
      "array": {
        "$objectToArray": {
          "a1": "ref1",
          "a2": "ref2"
        }
      },
      "uid": 1,
      
    }
  },
  {
    "$project": {
      "ref": {
        "$filter": {
          "input": "$array",
          "as": "elem",
          "cond": {
            "$eq": [
              "$$elem.k",
              "$uid"
            ]
          }
        }
      },
      uid: 1,
    },
  },
  {
    "$project": {
      ref: {
        "$arrayElemAt": [
          "$ref.v",
          0
        ]
      },
      uid: 1,
    }
  }
])

See it working here. I hope you get the idea and convert it into the nodejs equivalent version.