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mongodb - aggregating and unwinding foreign ref documents

So for my example database set up:

db.lists.insertMany([
_id: "1", name: "list1", included_lists: ["2"], items: ["i1"] ,
_id: "2", name: "list2", included_lists: , items: ["i2", "i3"]
])


db.items.insertMany([
_id: "i1", name: "item1", details: [, , ] ,
_id: "i2", name: "item2", details: [, , ] ,
_id: "i3", name: "item3", details: [, , ]
])


I'm currently getting my items data via:

db.lists.aggregate([
"$match": "_id": "$in": ["1", "2"] ,

"$lookup":
"from": "items",
"localField": "items",
"foreignField": "_id",
"as": "item"

,
"$unwind": "$item" ,

"$facet":
"results": [
"$skip": 0 ,
"$limit": 10 ,

"$project":
name: 1,
item: 1


],
"total": [
"$count": "total" ,
]


]).pretty()


which returns:


"results" : [

"_id" : "1",
"name" : "list1",
"item" :
"_id" : "i1",
"name" : "item1",
"details" : [


,


,



]

,

"_id" : "2",
"name" : "list2",
"item" :
"_id" : "i2",
"name" : "item2",
"details" : [


,


,



]

,

"_id" : "2",
"name" : "list2",
"item" :
"_id" : "i3",
"name" : "item3",
"details" : [


,


,



]


],
"total" : [

"total" : 3

]



What I'm trying to do, is remove the "$match": "_id": "$in": ["1", "2"] , as I want to remove the query needed to get the array of ids, and instead just get all the ids from list _id and its included_lists ids. Then have return all the items return like my result.

"$match": "_id": "$in": ["1", "2"] ,

_id

included_lists

items

This question is similar to: mongodb - unwinding nested subdocuments but I've reasked due to ambiguity and lack of db documents.

_id

included_lists

"2"

1 Answer
1

you can do it with graph lookup and then group

db.lists.aggregate([
"$match": "_id": "$in": ["1"] ,

$graphLookup:
from: "lists",
startWith: "$_id" ,
connectFromField: "included_lists",
connectToField: "_id",
as: "connected",

,

$unwind:"$connected",
$group:_id:"$connected._id",items:$first:'$connected.items',name:$first:'$connected.name',

"$lookup":
"from": "items",
"localField": "items",
"foreignField": "_id",
"as": "item"

,
"$unwind": "$item" ,

"$facet":
"results": [
"$skip": 0 ,
"$limit": 10 ,

"$project":
name: 1,
item: 1


],
"total": [
"$count": "total" ,
]






]).pretty()

$match

items

$unwind

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