Simplifying graphLookup output in MongoDB - mongodb

Question

I have a collection "people" in the form:
{ "_id" : 1, "name" : "Grandma"}
{ "_id" : 2, "name" : "Mum", "parentID": "1"}
{ "_id" : 3, "name" : "Uncle", "parentID": "1"}
{ "_id" : 4, "name" : "Kid", "parentID": "2"}
{ "_id" : 5, "name" : "Sister", "parentID": "2"}
To get the ancestors of a certain person (let's say Kid), I can use a simple match and graphLookup as follows:
people.aggregate([
{$match: {_id: "3"}},
{$graphLookup:
{
from: "people",
startWith: "$parentID",
connectFromField: "parentID",
connectToField: "_id",
as: "ancestors"
}
}
])
which will return
{ "_id" : 3, "name" : "Kid", "parentID": "2", "ancestors": [
{ "_id" : 1, "name" : "Grandma"},
{ "_id" : 2, "name" : "Mum", "parentID": "1"}]
}
Where I am stuck is how to refactor this output data into a single layered array, such that:
array = [
{ "_id" : 1, "name" : "Grandma"},
{ "_id" : 2, "name" : "Mum", "parentID": "1"},
{ "_id" : 3, "name" : "Kid", "parentID": "2"}
]
(array order isn't important).
Any help would be greatly appreciated!

Answer 1

Just need to change startWith from parentID to _id, this will return ancestors with current document
$project to show required fields
result = people.aggregate([
{ $match: { _id: "3" } },
{
$graphLookup: {
from: "collection",
startWith: "$_id",
connectFromField: "parentID",
connectToField: "_id",
as: "ancestors"
}
},
{
$project: {
_id: 0,
ancestors: 1
}
}
])
Playground
Access array by:
finalResult = result[0]['ancestors']