Supposedly I want to get a an object from my collection, an to this object, I want to add a property that will store an array of object containing ids and title matching one of the property of my object (in my case series).

Example I have this object as a result from my initial query

{
   _id: 13123123123,
   title: "TitleofObject",
   series: "SeriesName",
}

then I want to look on the same collection where the series name is the same for my object (add a new property named sameSeries to store objects matching the series) and the final result of object should look something like this

    _id: 13123123123,
   title: "TitleofObject",
   series: "SeriesName",
   sameSeries: 
    [
      {
      _id: 12312312,
      title: "anothertitleofObject"
      }, 
      {
      _id: 12312342312,
      title: "anothertitleofObject2"
      }
    ]
   

How can I achieve this using the aggregate method?

 const book = await Book.aggregate([
       {
            $match: { _id: id }
       },
])

CodePudding user response：

db.collection.aggregate([
  {
    "$group": { //Group by series
      "_id": "$series",
      "sameSeries": { //Create an object
        $push: { //push the required fields
          "title": "$title",
          "_id": "$_id"
        }
      }
    }
  }
])

playground

db.collection.aggregate([
  {
    "$match": {
      "_id": 13123123123,
      "sameSeries": {
        "$exists": false
      }
    }
  },
  {
    "$lookup": {
      "from": "collection",
      "localField": "series",
      "foreignField": "series",
      "as": "sameSeries"
    }
  }
])

Playground

To skip the parent id, you can do a slice

db.collection.aggregate([
  {
    "$match": {
      "_id": 13123123123,
      
    }
  },
  {
    "$lookup": {
      "from": "collection",
      "localField": "series",
      "foreignField": "series",
      "as": "sameSeries"
    }
  },
  {
    "$project": {
      _id: 1,
      series: 1,
      title: 1,
      sameSeries: {
        "$slice": [
          "$sameSeries",
          -1
        ]
      }
    }
  }
])

Play