db={"dashboard":[{"_id":"dashboard1"}],"templatefolders":[{"dashboardId":"dashboard1","folderId":"folder123"}],"folders":[{"_id":"folder123"}]}

db.dashboard.aggregate([{"$lookup":{"from":"templatefolders","localField":"_id","foreignField":"dashboardId","as":"joinDashboard"}},{"$unwind":"$joinDashboard"},{"$lookup":{"from":"folders","localField":"joinDashboard.folderId","foreignField":"_id","as":"joinDashboard.joinFolder"}},{"$group":{"_id":"$_id","joinDashboard":{"$push":"$joinDashboard"}}}])