Select a same field from a list of similar nested fields in mongoose

Question

I have a schema.

const placeSchema = new Schema({
    description: {
      fr: String,
      en: String,
    },
    comment: {
      fr: String,
      en: String,
    },
    ...
    ...
});

const Place= mongoose.model('Place', placeSchema);

module.exports = Place;

If I want to get only 'en' value I am currently using

await Place.find({}, '-description.fr -comment.fr ...')

If the number of similar fields increases so does the length of the query. Is there a way to select all the similar fields like maybe $field.fr?

Answer 1

Technically yes there is a way. using $objectToArray and doing some structure manipulation.

It would look something like this:

db.collection.aggregate([
  {
    $match: {} //match your document.
  },
  {
    $addFields: {
      rootArr: {
        $objectToArray: "$$ROOT"
      }
    }
  },
  {
    $unwind: "$rootArr"
  },
  {
    $match: {
      "rootArr.v.en": {
        $exists: true
      }
    }
  },
  {
    $group: {
      _id: "$_id",
      data: {
        $push: {
          k: "$rootArr.k",
          v: "$rootArr.v.en"
        }
      }
    }
  },
  {
    $replaceRoot: {
      newRoot: {
        $arrayToObject: "$data"
      }
    }
  }
])

Mongo Playground

It's a little "hacky" thought, how strict are your schema needs? Have you considered building it under the following structure?:

const placeSchema = new Schema({
    data: [
        {
            lang: String,
            description: String,
            comment: String,
            ...
        }
    ]
});