mongo $lookup

Mongo Join

Example

db.facility.aggregate([
   {
     $lookup:
       {
         from: "facilities",
         localField: "created_by",
         foreignField: "id",
         as: "maker"
       }
  }
])

Findone

[
   {
     $lookup:
       {
         from: "users",
         localField: "edited_by",
         foreignField: "id",
         as: "editor"
       }
  },
  { "$project": {
            "editor": { "$arrayElemAt": [ "$editor", 0 ] }
        }}
        
]

Also findone

How to use MongoDBs aggregate `$lookup` as `findOne()`

So as you all know, find() returns an array of results, with findOne() returning just a simply object. With Angular, this makes a huge difference. Instead of going {{myresult[0].name}}, I can simply

https://stackoverflow.com/questions/37691727/how-to-use-mongodbs-aggregate-lookup-as-findone

$lookup (aggregation) - MongoDB Manual

Performs a left outer join to an unsharded collection in the same database to filter in documents from the "joined" collection for processing. To each input document, the stage adds a new array field whose elements are the matching documents from the "joined" collection. The stage passes these reshaped documents to the next stage.

https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/