Find how many listings does the host have in the first records

Write a MongoDB query to find how many listings does the host have in the first records in the listingsAndReviews collection.

Structure of 'listingsAndReviews' collection:

 {
    _id: '10059872',
    listing_url: 'https://www.airbnb.com/rooms/10059872',
    name: 'Soho Cozy, Spacious and Convenient',
    summary: 'Clean, fully furnish, Spacious 1 bedroom flat just off the escalator in Mid Levels. 2 minutes From Soho Bar and Restaurants. Located in a quiet alley 1 minute from Sun Yat Sen',
    space: '',
    description: 'Clean, fully furnish, Spacious 1 bedroom flat just off the escalator in Mid Levels. 2 minutes From Soho Bar and Restaurants. Located in a quiet alley 1 minute from Sun Yat Sen',
    neighborhood_overview: '',
    notes: '',
    transit: '',
    access: '',
    interaction: '',
    house_rules: '',
    property_type: 'Apartment',
    room_type: 'Entire home/apt',
    bed_type: 'Real Bed',
    minimum_nights: '4',
    maximum_nights: '20',
    cancellation_policy: 'flexible',
    last_scraped: ISODate("2019-03-11T04:00:00.000Z"),
    calendar_last_scraped: ISODate("2019-03-11T04:00:00.000Z"),
    first_review: ISODate("2015-12-19T05:00:00.000Z"),
    last_review: ISODate("2018-03-27T04:00:00.000Z"),
    accommodates: 3,
    bedrooms: 1,
    beds: 2,
    number_of_reviews: 3,
    bathrooms: Decimal128("1.0"),
    amenities: [
      'Air conditioning',
      'Kitchen',
      'Smoking allowed',
      'Doorman',
      'Elevator',
      'Heating',
      'Family/kid friendly',
      'Essentials',
      '24-hour check-in',
      'translation missing: en.hosting_amenity_50'
    ],
    price: Decimal128("699.00"),
    weekly_price: Decimal128("5000.00"),
    extra_people: Decimal128("0.00"),
    guests_included: Decimal128("1"),
    images: {
      thumbnail_url: '',
      medium_url: '',
      picture_url: 'https://a0.muscache.com/im/pictures/4533a1dc-6fd8-4167-938d-391c6eebbc19.jpg?aki_policy=large',
      xl_picture_url: ''
    },
    host: {
      host_id: '51624384',
      host_url: 'https://www.airbnb.com/users/show/51624384',
      host_name: 'Giovanni',
      host_location: 'Hong Kong, Hong Kong',
      host_about: '',
      host_thumbnail_url: 'https://a0.muscache.com/im/pictures/264b82a7-756f-4da8-b607-dc9759e2a10f.jpg?aki_policy=profile_small',
      host_picture_url: 'https://a0.muscache.com/im/pictures/264b82a7-756f-4da8-b607-dc9759e2a10f.jpg?aki_policy=profile_x_medium',
      host_neighbourhood: 'Soho',
      host_is_superhost: false,
      host_has_profile_pic: true,
      host_identity_verified: false,
      host_listings_count: 1,
      host_total_listings_count: 1,
      host_verifications: [ 'email', 'phone', 'reviews', 'jumio', 'government_id' ]
    },
    address: {
      street: 'Hong Kong, Hong Kong Island, Hong Kong',
      suburb: 'Central & Western District',
      government_area: 'Central & Western',
      market: 'Hong Kong',
      country: 'Hong Kong',
      country_code: 'HK',
      location: {
        type: 'Point',
        coordinates: [ 114.15027, 22.28158 ],
        is_location_exact: true
      }
    },
    availability: {
      availability_30: 0,
      availability_60: 0,
      availability_90: 0,
      availability_365: 0
    },
    review_scores: {
      review_scores_accuracy: 10,
      review_scores_cleanliness: 10,
      review_scores_checkin: 10,
      review_scores_communication: 10,
      review_scores_location: 10,
      review_scores_value: 8,
      review_scores_rating: 100
    },
    reviews: [
      {
        _id: '56904633',
        date: ISODate("2015-12-19T05:00:00.000Z"),
        listing_id: '10059872',
        reviewer_id: '5302612',
        reviewer_name: 'Octavio',
        comments: 'The host canceled this reservation 11 days before arrival. This is an automated posting.'
      },
      {
        _id: '223175530',
        date: ISODate("2018-01-01T05:00:00.000Z"),
        listing_id: '10059872',
        reviewer_id: '48436743',
        reviewer_name: 'Ross',
        comments: 'Giovanni was very helpful and responsive to my questions. This is a great apartment that is very convenient for exploring Hong Kong.'
      },

      {
        _id: '247251577',
        date: ISODate("2018-03-27T04:00:00.000Z"),
        listing_id: '10059872',
        reviewer_id: '111288273',
        reviewer_name: 'Christian',
        comments: 'The host canceled this reservation 8 days before arrival. This is an automated posting.'
      }
    ]
  },
.......

Query:

db.listingsAndReviews.aggregate([
{ $match: {} },
{ $project: { host_listings_count: "$host.host_listings_count" } },
{ $limit: 1 }
])

Output:

[ { _id: '10009999', host_listings_count: 1 } ]

Explanation:

The said query in MongoDB returns an object that contains the host_listings_count field, which is the number of listings the host has in the first record in the listingsAndReviews collection.

The first stage of the aggregation pipeline $match matches all documents in the collection.

The second stage of the aggregation pipeline $project projects the host_listings_count field from the host subdocument.

The last stage of the aggregation pipeline $limit: 1 limits the results to only the first document.

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