I have the following Schema:

const PublicationSchema = mongoose.Schema({
    title: {
        type: String,
        required: true
    },
    files:[{ 
        contentType: String, 
        data: Buffer,
        name: String
    }]

})

What I'm trying to do is to get the file with the same index as the query.For example I have this object:

  _id: new ObjectId("637f20ce6ce5c48d9788a1ff"),
  title: 'TEST',
  files: [
    {
      contentType: 'application/pdf',
      name: 'imId1',
      _id: new ObjectId("id1")
    },
    {
      contentType: 'application/pdf',
      name: 'imId2',
      _id: new ObjectId("id2")
    }
  ]

where if I query id2 it only retrieves:

    {
      contentType: 'application/pdf',
      name: 'imId2',
      _id: new ObjectId("id2")
    }

What I was trying to use was const onePublication = await Publication.findOne({ "files._id": req.body.fileId},{}) but this retrieves every field.

I was going to just tell it to not retrieve the other field using field:0 but I realized that this will still retrieve the files in other indexes of the field.

Is there a way to tell it to only retrieve the one with the same index or should I be using another query entirely?

CodePudding user response：

One of the options is to $unwind the array first. $match by your criteria. Then, $replaceRoot to get your array entry.

db.collection.aggregate([
  {
    "$unwind": "$files"
  },
  {
    $match: {
      "files._id": "id2"
    }
  },
  {
    "$replaceRoot": {
      "newRoot": "$files"
    }
  }
])

Mongo Playground

Consider changing your schema to store files as an individual collection, if most of the time you are going to access the array objects only.