I'm having a Model which is structured similar to this:
{
"_id": ObjectId("5c878c5c18a4ff001b981zh5"),
"books": [
ObjectId("5d963a7544ec1b122ab2ddc"),
ObjectId("5d963be01f663d168f8ea4dc"),
ObjectId("5d963bcb1f663d168f8ea2f4"),
ObjectId("5d963bdf1f663d16858ea7c9"),
}
Now I want to use the aggregation framework to get a list of only the populated books, like:
{ _id: ObjectId("5d963a7544ec1b122ab2ddc"), title: ...., ... },
..
.aggregate([
{
$lookup: {
from: 'books',
let: { books: '$books' },
pipeline: [{ $match: { $expr: { _id: { $in: ['_id', '$$books'] } } } }],
as: 'bookInfos'
}
},
{ $unwind: '$bookInfos' },
{ $replaceRoot: { newRoot: '$bookInfos' } }
])
I am not too sure about your question, but I think this might be what you're looking for.
So this query worked for me:
{
$match: {
_id: user._id,
},
},
{
$lookup: {
from: "books",
localField: "books",
foreignField: "_id",
as: "booksInfo",
},
},
{ $unwind: "$booksInfo" },
{
$replaceRoot: {
newRoot: "$booksInfo",
},
},
Thanks #zishone. Somehow your query returned all the books available in the db and not only the ones from the User Model, but it works as desired when looking up the documents with local and foreignField.
Related
I have these collections:
author
[
{
_id: "63c242130b17d5516e0cb499",
author_name:'Vyom',
book_ids:["63c242330b17d5516e0cb49a","63c242410b17d5516e0cb49b"]
}
]
book
[
{
_id:"63c242330b17d5516e0cb49a",
author_id:'63c242130b17d5516e0cb499',
book_name:'True Love',
genere:'horror'
},
{
_id:"63c242410b17d5516e0cb49b",
author_id:'63c242130b17d5516e0cb499',
book_name:'Monster Strike',
genere:'romance'
},
]
I want to fetch details of books in author collection aggregation if book_ids exists.
For this I tried as:
db.author.aggregate([
{
$match: {
_id: ObjectId("63c242130b17d5516e0cb499")
}
},
{
$lookup:{
from: 'book',
localField: '_id',
foreignField: 'author_id',
as: 'book_details'
}
},
{
$addFields:{
book_info: {
$map: {
input: '$book_details'
as: 'el'
in: {
$match: {_id:ObjectId('$$el._id')},
$paroject: {book_name: 1},
}
}
}
}
}
])
But it throws:
Unrecognized error: '$match'.
Expected O/P:
[
{
_id: "63c242130b17d5516e0cb499",
author_name:'Vyom',
book_ids:["63c242330b17d5516e0cb49a","63c242410b17d5516e0cb49b"],
book_info: [
{
_id:"63c242330b17d5516e0cb49a",
book_name:'True Love',
},
{
_id:"63c242410b17d5516e0cb49b",
book_name:'Monster Strike',
}
]
}
]
Is there any other way to loop and get details? I tried looking for other solutions but was unable to find.
I don't see why you need a $set stage to format the element in the book_details array for the book_info field.
You can use $lookup with pipeline to join both collections and format the array of documents returned.
db.author.aggregate([
{
$match: {
_id: ObjectId("63c242130b17d5516e0cb499")
}
},
{
$lookup: {
from: "book",
localField: "book_ids",
foreignField: "_id",
as: "book_info",
pipeline: [
{
$project: {
_id: 1,
book_name: 1
}
}
]
}
}
])
Demo # Mongo Playground
db.authors.aggregate([
{
$lookup: {
from: "books",
localField: "book_ids",
foreignField: "_id",
as: "books"
}
},
{
$match: { "books": { $ne: [] } }
},
{
$project: {
_id: 1,
author_name: 1,
books: {
_id: 1,
author_id: 1,
book_name: 1,
genre: 1
}
}
}
])
This pipeline will give you the result where all the authors' book details will be there if they have any books
I have two collections in my mongoDb database, one called media, one called users.
Documents in the media collection:
{"_id":{"$oid":"6379204a8cf5677554c26c1b"},"_partition":"6378eb74f6613d5d4192da79","name":"silas test"}
{"_id":{"$oid":"6378eb74f6613d5d4192da79"},"_partition":"6378eb74f6613d5d4192da79","name":"test media"}
Document in the users collection:
{
"_id":{
"$oid":"6379ee6c770a8f43afc8e3e4"},
"_partition":"6378eb74f6613d5d4192da79",
"types":[
{
"mediaReference":[
{"$oid":"6379204a8cf5677554c26c1b"}
],
"mediatype":"podcast"
},
{
"mediaReference":[
{"$oid":"6378eb74f6613d5d4192da79"}
],
"mediatype":"movie"
}
],
"username":"silas"
}
Now im looking for a way to use the mongoDb aggregation pipeline to get the following result:
{
"_id":{
"$oid":"6379ee6c770a8f43afc8e3e4"},
"_partition":"6378eb74f6613d5d4192da79",
"types":[
{
"mediaReference":[
{
"_id": {
"$oid":"6379204a8cf5677554c26c1b"
},
"_partition":"6378eb74f6613d5d4192da79",
"name":"silas test"
}
],
"mediatype":"podcast"
},
{
"mediaReference":[
{
"_id": {
"$oid":"6378eb74f6613d5d4192da79"
},
"_partition":"6378eb74f6613d5d4192da79",
"name":"test media"
}
],
"mediatype":"movie"
}
],
"username":"silas"
}
Basically im searching for a way to paste the refferenced document into the mediaReference object inside the users document.
i would appreciate any help
EDIT:
I've found the solution:
db.users.aggregate([{
$unwind: {
path: '$types'
}
}, {
$lookup: {
from: 'media',
localField: 'types.mediaReference',
foreignField: '_id',
as: 'types.mediaReference'
}
}, {
$group: {
_id: '$_id',
merged: {
$first: '$$ROOT'
},
types: {
$push: '$types'
}
}
}, {
$addFields: {
'merged.types': '$types'
}
}, {
$replaceRoot: {
newRoot: '$merged'
}
}])
I have collections like this:
// tasks
[
{_id: '123', _user: '345', _solutions: ['567', '678'] }
]
// solutions
[
{ _id: '567', _task: '123', _user: '345' },
{ _id: '678', _task: '123', _user: '345' }
]
// users
[
{ _id: '345', name: 'Tom' }
]
With this code:
await db
.collection<Task>('tasks')
.aggregate([
{ $match: { _id: id } },
{
$lookup: {
from: 'solutions',
// I guess here should be pipeline
localField: '_solutions',
foreignField: '_id',
as: '_solutions',
},
},
{ $lookup: { from: 'users', localField: '_user', foreignField: '_id', as: '_user' } },
])
I have result as below:
task = {
_id: 5e14e877fa42402079e38e44,
_solutions: [
{
_id: 5e15022ccafcb4869c153e61,
_task: 5e14e877fa42402079e38e44,
_user: 5e007403fd4ca4f47df69913, <-- this should be userObject instead
},
{
_id: 5e164f31cafcb4869c153e62,
_task: 5e14e877fa42402079e38e44,
_user: 5e007403fd4ca4f47df69913, <-- this should be userObject instead
}
],
_user: [
{
_id: 5e007403fd4ca4f47df69913,
_solutions: [Array],
_tasks: [Array],
}
]
}
and I don't know how to $lookup into _solutions._user - so instead of objectId I will have exact user object.
You can run $lookup with custom pipeline for outer lookup and the regular one for users:
db.tasks.aggregate([
{
$match: {
_id: "123"
}
},
{
$lookup: {
from: "solutions",
let: { solutions: "$_solutions" },
pipeline: [
{ $match: { $expr: { $in: [ "$_id", "$$solutions" ] } } },
{
$lookup: {
from: "users",
localField: "_user",
foreignField: "_id",
as: "_user"
}
},
{ $unwind: "$_user" }
],
as: "_solutions",
}
}
])
Mongo Playground
I'm making a blog and have an query about which would give me better performace, simple lookup or lookup with pipeline because sometime simple lookup gave me fast result and sometime pipleline lookup. So, I am bit confused now which one to use or where to use. Suppose I have 2 collection, user and comment collection.
// Users Collection
{
_id: "MONGO_OBJECT_ID",
userName: "Web Alchemist"
}
// Comments Collection
{
_id: "MONGO_OBJECT_ID",
userId: "USER_MONGO_OBJECT_ID",
isActive: "YES", // YES or NO
comment: "xyz"
}
Now I want to Lookup from users collection to comments, which one would be better for this. I made two query which giving me same result.
[
{
$match: { _id: ObjectId("5d68c019c7d56410cc33b01a") }
},
{
$lookup: {
from: "comments",
as: "comments",
localField: "_id",
foreignField: "userId"
}
},
{
$unwind: "$comments"
},
{
$match: {
"comments.isActive": "YES"
}
},
{ $limit: 5},
{
_id: 1, userName: 1, comments: { _id: "$comments._id", comment: "$comments.comment"}
},
{
$group: {
_id: "$_id",
userName: { '$first': '$userName' },
comments: { $addToSet: "comments"}
}
}
]
OR
[
{
$match: { _id: ObjectId("5d68c019c7d56410cc33b01a") }
},
{
$lookup: {
from: "comments",
as: "comments",
let: { userId: "$_id" },
pipeline: [
{
$match: {
$expr: {
$and: [
{ $eq: ['$userId', '$$userId'] },
{ $eq: ['$isActive', 'YES'] }
]
}
}
},
{ limit: 5 },
{
$project: { _id: 1, comment: 1 }
}
]
}
}
]
The idea here is to return an array of documents of the users' followers with the information if this user is a friend of that follower or not.
So far I have:
db.getCollection('users').aggregate([
{ $match: { _id: ObjectId("588877d82523b4395039910a") } },
{ $lookup: {
from: 'users',
localField: 'followers',
foreignField: '_id',
as: 's_followers'
}
},
{
$project: {
"s_followers._id": 1,
"s_followers.isFriend": {
$in: ["s_followers.id",
{ $setIntersection: ["$friends", "$followers"] }
]}
}
}
])
But the "s_followers.id" used in the $in operator doesn't seem to retrieve the _id information from the follower, so it always returns false.
When I use a ObjectId directly, I got the result I want:
"s_followers.isFriend": {
$in: [ObjectId("588877d82523b4395039910a"),
{ $setIntersection: ["$friends", "$followers"] }
]}
But I really need this ID to be a reference to the follower _id.
Expected result would be something like:
{
"_id" : ObjectId("588877d82523b4395039910a"),
"s_followers" : [
{
"_id" : ObjectId("5888687e56be8f172844d96f"),
"isFriend" : true
},
{
"_id" : ObjectId("5888ca27d79b8b03949a6e8c"),
"isFriend" : false
}
]
}
Thanks for your help!
UPD: A different approach (maybe easier), would be to use the ID of the user that I have (the one used on $match), but I would still need to get the reference for the follower's follower array
db.getCollection('users').aggregate([
{ $match: { _id: ObjectId("588877d82523b4395039910a") } },
{ $lookup: {
from: 'users',
localField: 'followers',
foreignField: '_id',
as: 's_followers'
}
}, {
$project: {
"firstName": 1,
"s_followers._id": 1,
"s_followers.firstName": 1,
"s_followers.followers": 1,
"s_followers.isFriend": { $in: [ObjectId("588877d82523b4395039910a"), "$s_followers.followers"] }
}
}
])
UPD2: The user data structure (the part that matters)
{
followers: [{ type: mongoose.Schema.Types.ObjectId, ref: "User" }],
friends: [{ type: mongoose.Schema.Types.ObjectId, ref: "User" }],
}
FOR VERSION 3.4.0+
Ok, just got it, I'll post here the code and my understanding of it:
db.getCollection('users').aggregate([
{ $match: { _id: ObjectId("588877d82523b4395039910a") } },
{ $lookup: {
from: 'users',
localField: 'followers',
foreignField: '_id',
as: 's_followers'
}
}, {
$project: {
"firstName": 1,
"s_followers._id": 1,
"s_followers.firstName": 1,
"s_followers.followers": 1,
}
}, {
$unwind: "$s_followers"
}, {
$project: {
"firstName": "$s_followers.firstName",
"isFriend": { $in: [ObjectId("588877d82523b4395039910a"), "$s_followers.followers"] }
}
}
])
My understanding of it:
$match: match the user I'm intended to get the followers of.
$lookup: found each follower detail
$project: select the information I want to return, also get the follower list of each follower
$unwind: create a different document for each follower
With the array unwinded, I can refer to the follower's followers array, and find my object id in it :)
In my example use followers friends list to check current user is friend or not. as {$arrayElemAt:["$s_followers.friends",0]} if want to find in followers then can use "$s_followers.followers"
You can try it.
db.getCollection('user').aggregate([
{ $match: { _id: ObjectId("5714d190e6128b7e7f8d9008") } },
{$unwind:"$followers"},
{ $lookup: {
from: 'user',
localField: 'followers',
foreignField: '_id',
as: 's_followers'
}
},
{$project:{
firstName:1,
s_followers:{$arrayElemAt:["$s_followers",0]},
isFriend:{$cond:[{
$anyElementTrue:{
$map: {"input": {$arrayElemAt:["$s_followers.friends",0]},
"as": "el",
"in": { "$eq": [ "$$el", "$_id" ] }
}
}
},true,false]}
}
},
{$group:{
_id:"$_id",
s_followers:{$push:{_id:"$s_followers._id",isFriend:"$isFriend"}}
}
}
])