MongoDB $geoNear Aggregation on another collection

Question

I have a database with two collections like so:

[
  {
    "name": "Person A",
    "location": {"type": "Point", "coordinates": [180, 90]}
  },
  {
    "name": "Person B",
    "location": {"type": "Point", "coordinates": [-180, -90]}
  }
]

[
  {
    "name": "Store A",
    "location": {"type": "Point", "coordinates": [180, 90]}
  },
  {
    "name": "Store B",
    "location": {"type": "Point", "coordinates": [-180, -90]}
  }
]

For each person, I want to find the nearest place. I could get it to find the nearest place for one specific pair of coordinates, not for the entire collection. Is there any way to do that without using foreach ? This is the closest I got following the MongoDB documentation :

// Current $geoNear:
{
  // Instead of having to give constants of a single
  // point, I want to compare against all coordinates
  // of another collection.              ↓
  near: {"type":"Point","coordinates":[-180, 90]},
  distanceField: 'distance',
  maxDistance: 50,
  spherical: true
}

Answer 1

This can be achieved using aggregation.

[{
$lookup: {
  from: "places",
  let: {
    "personPoint": "$location"
  },
  as: "nearestPlace",
  pipeline: [
    {
      $geoNear: {
        near: "$$personPoint",
        spherical: true,
        distanceField: "distance",
        maxDistance: 50,
        
      }
    },
    {
      $unwind: "$location"
    },
    
  ]
 }
},
{
 $unwind: {
  path: "$nearestPlace",
  preserveNullAndEmptyArrays: true
 }
}]

I couldn't test it on playground because of geo index. So might require some minor fix. If anyone can make it work on playground heres the link https://mongoplayground.net/p/aROX976gYzC