db.people.insertMany([{_id: 0, name: "Jan", friends: ["Sara", "Martin"], hobbies: "tennis"},
{_id: 1, name: "Martin", friends: ["Ken", "Andrew"], hobbies: "cycling"},
{_id: 2, name: "Sara", friends: ["Ken", "Jenniffer"], hobbies: "travel"},
{_id: 3, name: "Ken", friends: ["Sara", "Andrew"], hobbies: "cycling"}]);

db.createView("peopleViewFacet", "people",
[{$facet: {"peopleWithFriends": [{$project: {name:1, friends:1}}]}},
{$unwind: "$peopleWithFriends"},
{$project: {"_id": "$peopleWithFriends._id", "name": "$peopleWithFriends.name", "friends": "$peopleWithFriends.friends"}}]);

let graphLookupStage = {$graphLookup: {
from: "peopleViewFacet",
startWith: "$friends",
connectFromField: "friends",
connectToField: "name",
maxDepth: 3,
as: "friendsCircle"} };

let projectStage = {$project: {"name": 1, "friends": 1, "socialCircle" : "$friendsCircle.name"}};

// The following aggregation contains a $facet inside a $facet and is expected to give an error, but it works.
db.people.aggregate([
{ "$facet" : {"result" : [ graphLookupStage, projectStage]}}]);

// Result
{ "result" : [ { "_id" : 0, "name" : "Jan", "friends" : [ "Sara", "Martin" ], "socialCircle" : [ "Martin", "Sara", "Ken" ] }, ... }