Embed root field in a subdocument within an aggregation pipeline - mongodb

Question

Maybe someone can help me with Mongo's Aggregation Pipeline. I am trying to put an object in another object but I'm new to Mongo and ist very difficult:
{
"_id" : ObjectId("5888a74f137ed66828367585"),
"name" : "Unis",
"tags" : [...],
"editable" : true,
"token" : "YfFzaoNvWPbvyUmSulXfMPq4a9QgGxN1ElIzAUmSJRX4cN7zCl",
"columns" : [...],
"description" : "...",
"sites" : {
"_id" : ObjectId("5888ae2f137ed668fb95a03d"),
"url" : "www.....de",
"column_values" : [
"University XXX",
"XXX",
"false"
],
"list_id" : ObjectId("5888a74f137ed66828367585")
},
"scan" : [
{
"_id" : ObjectId("5888b1074e2123c22ae7f4d3"),
"site_id" : ObjectId("5888ae2f137ed668fb95a03d"),
"scan_group_id" : ObjectId("5888a970a7f75fbd49052ed6"),
"date" : ISODate("2017-01-18T16:00:00Z"),
"score" : "B",
"https" : false,
"cookies" : 12
}
]
}
I want to put every object in the "scan"-array into "sites". So that it looks like this:
{
"_id" : ObjectId("5888a74f137ed66828367585"),
"name" : "Unis",
"tags" : [...],
"editable" : true,
"token" : "YfFzaoNvWPbvyUmSulXfMPq4a9QgGxN1ElIzAUmSJRX4cN7zCl",
"columns" : [...],
"description" : "...",
"sites" : {
"_id" : ObjectId("5888ae2f137ed668fb95a03d"),
"url" : "www.....de",
"column_values" : [
"University XXX",
"XXX",
"false"
],
"list_id" : ObjectId("5888a74f137ed66828367585"),
"scan" : [
{
"_id" : ObjectId("5888b1074e2123c22ae7f4d3"),
"site_id" : ObjectId("5888ae2f137ed668fb95a03d"),
"scan_group_id" : ObjectId("5888a970a7f75fbd49052ed6"),
"date" : ISODate("2017-01-18T16:00:00Z"),
"score" : "B",
"https" : false,
"cookies" : 12
}
]
}
}
Is there a step in the aggregation pipeline to perform this task?

Answer 1

With a single pipeline I don't see any other way but specifying each field individually as:
db.collection.aggregate([
{
"$project": {
"name": 1, "tags": 1,
"editable": 1,
"token": 1, "columns": 1,
"description": 1,
"sites._id": "$sites._id",
"sites.url": "$sites.url" ,
"sites.column_values": "$sites.column_values" ,
"sites.list_id": "$sites.list_id",
"sites.scan": "$scan"
}
}
])
With MongoDB 3.4 and newer, you can use the $addFields pipeline step instead of specifying all fields using $project. The advantage is that it adds new fields to documents and outputs documents that contain all existing fields from the input documents and the newly added fields:
db.collection.aggregate([
{
"$addFields": {
"sites._id": "$sites._id",
"sites.url": "$sites.url" ,
"sites.column_values": "$sites.column_values" ,
"sites.list_id": "$sites.list_id",
"sites.scan": "$scan"
}
}, { "$project": { "scan": 0 } }
])