mongo $lookup


## Mongo Join
### Example
```typedb.facility.aggregate([   {     $lookup:       {         from: "facilities",         localField: "created_by",         foreignField: "id",         as: "maker"       }  }])```

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


### Also findone
> [How to use MongoDBs aggregate `$lookup` as `findOne()`](https://stackoverflow.com/questions/37691727/how-to-use-mongodbs-aggregate-lookup-as-findone)

> [$lookup (aggregation) - MongoDB Manual](https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/)
