How to select parent based on children's value using mongoose and GraphQL?

I'm trying to achieve something equivalent to a conditional JOIN query, but then with GraphQL. I'm using Mongoose for my db model and MongoDB as database.

I'll illustrate my problem with the following graphQL schema:

type Booking {
    _id: ID!
    client: Client!
    rooms: Room!
    activities: Activity!
    nrOfAdults: Int!
    arrivalDate: String!
    departureDate: String!
}

type Room {
  _id: ID!
  name: String!
  contents: String
  priceNight: Float!
  maxAdults: Int!
  reservations: [Booking]
}

The Mongoose schema:

const bookingSchema = new Schema(
  {
    client: {
      type: Schema.Types.ObjectId,
      ref: 'Client'
    },
    rooms: [{
      type: Schema.Types.ObjectId,
      ref: 'Rooms'
    }],
    nrOfAdults: {
      type: Number,
      required: true
    },
    arrivalDate: {
      type: Date,
      required: true
    },
    departureDate: {
      type: Date,
      required: true
    }
  },
  { timestamps: true }
);

const roomSchema = new Schema({
  name: {
    type: String,
    required: true
  },
  priceNight: {
    type: Number,
    required: true
  },
  maxAdults: {
    type: Number,
    required: true
  },
  reservations: [
    {
      type: Schema.Types.ObjectId,
      ref: 'Booking'
    }
  ]
});

I can query rooms, for example, if I want to get the rooms for 3 or more adults I run:

       Room.find({
         maxAdults: { $gte: 3 }
       });

This works fine.

However, I'd also like to show the available rooms, which means I need to impose a condition on the booking objects which are hold in reservation. I thought this would be fairly easy, using something like:

       Room.find({
         maxAdults: { $gte: 3 },
         reservations: { $elemMatch: { arrivalDate: { $gte: *some date*}}}
       });

But it returns an empty array, while it should return some value, based on the data in mongodb:

To make things a little more clear, I'd like to achieve the same outcome as the following SQL query would give me:

SELECT *
FROM room
JOIN booking ON room.id = booking.roomId
WHERE
room.maxAdults >= 3
AND
(
booking.arrivalDate > CAST('2020-05-15' AS DATE)
OR
booking.departureDare < CAST(2020-05-06' AS DATE)
)

Assuming that you have saved the values similar to what you have mentioned in the mongoose schema.

Explore the how to do join in mongodb. Aim is to do the join before executing the query on the sub fields from the different collection.

Relevant Answer: How do I perform the SQL Join equivalent in MongoDB?

I suggest using aggregate pipeline for accomplishing what you want.

Suggested code :

Room.aggregate([
    {
        $match: {
            maxAdults: { $gte: 3 }
        }
    },
    {
        $lookup: {
            from: "bookings",
            localField: "reservations",
            foreignField: "_id",
            as: "booking"
        }
    },
    {
        $unwind: '$booking'
    },
    {
        $match: {
          booking.arrivalDate: { $gte: *some date* }
        }
    },
])