Excract only the lookup's return (mongoose)

Question

So I have two collections in my mongodb.

   // Collection 1, named Event
   {
        "_id": "625335297fcc20782bcdf085",
        "title": "Evento 1",
        "description": "lorem ipsum evento 1",
        "img": "nao implementado",
        "value": 0,
        "remainingVacancies": 14,
        "isSingleDay": false,
        "dateByDay": [
            {
                "initialDate": "2022-04-10T21:17:09.785Z",
                "finalDate": "2022-04-10T21:17:09.785Z",
                "_id": "62534955171ecadae7ff6cd4"
            },
            {
                "initialDate": "2022-04-10T21:17:09.785Z",
                "finalDate": "2022-04-10T21:17:09.786Z",
                "_id": "62534955171ecadae7ff6cd5"
            }
        ],
        "__v": 0
    }

and

   // Collection 2, named Presentation
   {
        "_id": "62549d4d3b41827fe7593332",
        "title": "Apresentação 1",
        "description": "lorem ipsum 11 testee",
        "img": "nao implementado",
        "value": 0,
        "remainingVacancies": 14,
        "isSingleDay": true,
        "dateByDay": [
            {
                "initialDate": "2022-04-11T21:27:41.823Z",
                "finalDate": "2022-04-11T21:27:41.823Z",
                "_id": "62549d4d3b41827fe7593333"
            }
        ],
        "eventId": "625335297fcc20782bcdf085",
        "__v": 0
    }

I've tried to use lookup aggregation in Event like this:

Event.aggregate([
    {
      $match: {
        _id: mongoose.Types.ObjectId(_id)
      },
    },
    {
      $lookup: {
        from: 'presentations',
        localField: '_id',
        foreignField: 'eventId',
        as: 'registeredPresentations'
      },
    },
    {
      $unwind: "$registeredPresentations"
    },
    {
      $project: {
        _id: 0,
        registeredPresentations: 1
      }
    },
  ]);

It returns this output

   {
        "registeredPresentations": {
            "_id": "6254900aa5b5977e99498ee0",
            "title": "Apresentação 1",
            "description": "lorem ipsum 22 testee",
            "img": "nao implementado",
            "value": 0,
            "remainingVacancies": 14,
            "isSingleDay": true,
            "dateByDay": [
                {
                    "initialDate": "2022-04-11T20:31:06.324Z",
                    "finalDate": "2022-04-11T20:31:06.324Z",
                    "_id": "6254900aa5b5977e99498ee1"
                }
            ],
            "eventId": "625335297fcc20782bcdf085",
            "__v": 0
        }
    },

But since I have multiples presentations related in one Event, I don't want the value returns as a object of "registeredPresentations". What I want is use lookup to extract the return without the "registeredPresentations" in the output, just like that:

   {
        "_id": "62549d4d3b41827fe7593332",
        "title": "Apresentação 1",
        "description": "lorem ipsum 11 testee",
        "img": "nao implementado",
        "value": 0,
        "remainingVacancies": 14,
        "isSingleDay": true,
        "dateByDay": [
            {
                "initialDate": "2022-04-11T21:27:41.823Z",
                "finalDate": "2022-04-11T21:27:41.823Z",
                "_id": "62549d4d3b41827fe7593333"
            }
        ],
        "eventId": "625335297fcc20782bcdf085",
        "__v": 0
    },

There's a way to extract this value without the "registeredPresentations" in the output?

score 0 · Accepted Answer · answered Apr 12 '22 at 01:13

0

Use $replaceWith

db.orders.aggregate([
  {
    $match: {
      _id: "625335297fcc20782bcdf085"
    }
  },
  {
    $lookup: {
      from: "presentations",
      localField: "_id",
      foreignField: "eventId",
      as: "registeredPresentations"
    }
  },
  {
    $unwind: "$registeredPresentations"
  },
  {
    $project: {
      _id: 0,
      registeredPresentations: 1
    }
  },
  {
    $replaceWith: "$registeredPresentations"
  }
])

mongoplayground

answered Apr 12 '22 at 01:13

YuTing

6,555
2
6
16

Your answer is not essentially different from the accepted answer and the other solutions in the marked duplicate and not very useful since it does not add any new value or information. Please avoid writing duplicate answers as this will ensure all questions and answers on the site remain useful not scattered/duplicated. – chridam Apr 14 '22 at 09:19

Excract only the lookup's return (mongoose)

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