I have a collection matches like this. I'm using players object {key: ObjectId, key: ObjectID} instead of classic array [ObjectId, ObjectID] for reference players collection
{
"_id": ObjectId("5eb93f8efd259cd7fbf49d55"),
"date": "01/01/2020",
"players": {
"home": ObjectId("5eb93f8efd259cd7fbf49d59"),
"away": ObjectId("5eb93f8efd259cd7fbf49d60")
}
},
{...}
And players collection:
{
"_id": ObjectId("5eb93f8efd259cd7fbf49d59"),
"name": "Roger Federer"
"country": "Suiza"
},
{
"_id": ObjectId("5eb93f8efd259cd7fbf49d60"),
"name": "Rafa Nadal"
"country": "España"
},
{...}
What's the better way to do mongoDB lookup? something like this is correct?
const rows = await db.collection('matches').aggregate([
{
$lookup: {
from: "players",
localField: "players.home",
foreignField: "_id",
as: "players.home"
}
},
{
$lookup: {
from: "players",
localField: "players.away",
foreignField: "_id",
as: "players.away"
},
{ $unwind: "$players.home" },
{ $unwind: "$players.away" },
}]).toArray()
I want output like this:
{
_id: 5eb93f8efd259cd7fbf49d55,
date: "12/05/20",
players: {
home: {
_id: 5eb93f8efd259cd7fbf49d59,
name: "Roger Federer",
country: "Suiza"
},
away: {
_id: 5eb93f8efd259cd7fbf49d60,
name: "Rafa Nadal",
country: "España"
}
}
}
{...}
You can try below aggregation query :
db.matches.aggregate([
{
$lookup: {
from: "players",
localField: "players.home",
foreignField: "_id",
as: "home"
}
},
{
$lookup: {
from: "players",
localField: "players.away",
foreignField: "_id",
as: "away"
}
},
/** Check output of lookup is not empty array `[]` & get first doc & write it to respective field, else write the same value as original */
{
$project: {
date: 1,
"players.home": { $cond: [ { $eq: [ "$home", [] ] }, "$players.home", { $arrayElemAt: [ "$home", 0 ] } ] },
"players.away": { $cond: [ { $eq: [ "$away", [] ] }, "$players.away", { $arrayElemAt: [ "$away", 0 ] } ] }
}
}
])
Test : mongoplayground
Changes or Issues with current Query :
1) As you're using two $unwind stages one after the other, If anyone of the field either home or away doesn't have a matching document in players collection then in the result you don't even get actual match document also, But why ? It's because if you do $unwind on [] (which is returned by lookup stage) then unwind will remove that parent document from result, To overcome this you need to use preservenullandemptyarrays option in unwind stage.
2) Ok, there is another way to do this without actually using $unwind. So do not use as: "players.home" or as: "players.away" cause you're actually writing back to original field, Just in case if you don't find a matching document an empty array [] will be written to actual fields either to "home" or "away" wherever there is not match (In this case you would loose actual ObjectId() value existing in that particular field in matches doc). So write output of lookup to a new field.
Or even more efficient way, instead of two $lookup stages (Cause each lookup has to go through docs of players collection again & again), you can try one lookup with multiple-join-conditions-with-lookup :
db.matches.aggregate([
{
$lookup: {
from: "players",
let: { home: "$players.home", away: "$players.away" },
pipeline: [
{
$match: { $expr: { $or: [ { $eq: [ "$_id", "$$home" ] }, { $eq: [ "$_id", "$$away" ] } ] } }
}
],
as: "data"
}
}
])
Test : mongoplayground
Note : Here all the matching docs from players which match with irrespective of away or home field will be pushed to data array. So to keep DB operation simple you can get that array from DB along with actual matches document & Offload some work to code which is to map respective objects from data array to players.home & players.away fields.
Related
I have two collections that I want to join with $lookup based on two id fields. Both fields are from type guid and looke like this in mongodb compass: 'Binary('cavTZa/U2kqfHtf08sI+Fg==', 3)'
This syntax in the compass aggregation pipeline builder gives the expected result:
{
from: 'clients',
localField: 'ClientId',
foreignField: '_id',
as: 'ClientData'
}
But i want to add some projection and tried to change it like this:
{
from: 'clients',
'let': {
id: '$_id.clients'
},
pipeline: [
{
$match: {
$expr: {
$eq: [
'$ClientId',
'$$id'
]
}
}
},
{
$project: {
Name: 1,
_id: 0
}
}
],
as: 'ClientData'
}
But the result here is that every client from collection 'clients' is added to every document in the starting table. I have to use MongoDB 3.6 so the new lookup syntax from >=5.0 is not available.
Any ideas for me? Does $eq work for binary stored guid data?
In the first example, you say that the local field is ClientId and the foreign field is _id. But that's not what you used in your second example.
This should work better:
{
from: 'clients',
'let': {
ClientId: '$ClientId'
},
pipeline: [
{
$match: {
$expr: {
$eq: [
'$$ClientId',
'$_id'
]
}
}
},
{
$project: {
Name: 1,
_id: 0
}
}
],
as: 'ClientData'
}
I just need following output
{
message: "Details are:",
status: 1,
data:[
{
leadId: "92106",
projectName: "Sales Rep Mobile App with Shopify Backend"
projectOverview: "<any description>"
notificationsData:[
{
_id:"6076e2593580d805814c338e",
content:"<strong>User Jangid</strong> posted a comment about this message on estimation portal.",
estimationId:"5f75a496c70f05559088d971",
commentId:"6076e2583580d805814c338b",
commentData:{
_id:"6076e2583580d805814c338b",
content:"<p>hello krishna this is and this is second </p>\n"
}
},
{
_id:"6077c7c75c1bfc051f8dff3e",
content:"<strong>User Nunna</strong> posted a comment about this message on estimation portal.",
estimationId:"5f75a496c70f05559088d971",
commentId:"6077c7c35c1bfc051f8dff3b",
commentData:{
_id:"6077c7c35c1bfc051f8dff3b",
content:"<p>hey hiiii</p>\n\n<p> </p>\n"
}
},
],
userName:"user Nunna",
profileImage:"profile url",
isViewed:true,
isSortByStatus:2,
isNotifyEst:1
}
]
}
In the above example i have multiple list of same type of collection
and this list is i aggregate with Estimation Collection
These Above Data if fetched based on Estimation Collection
so based on this Estimation Collection's _id i need to fetch notification and based on commentId that fetched inside notification collection i need to fetch comments collection data.
i already do aggregation with some more collection i only need the notification and comment data inside notificationData array
Yes i Achieve this i use following query for that
let estData = await Estimations.aggregate([
{
$lookup: {
from: "notifications", as: "notificationsData",
let: {
estimation_id: "$_id"
},
pipeline: [
{
$match: {
$expr: {
$and: [
{ $eq: ['$estimationId', "$$estimation_id"] },
{ $eq: ['$userId', ObjectId(this.req.currentUser._id)] },
{ $eq: ['$isViewed', false] },
]
}
},
},
{
$lookup:
{
from: "comments",
localField: "commentId",
foreignField: "_id",
as: "commentData"
}
},
{ "$unwind": "$commentData" },
],
}
},
{
$project: {
projectName: 1,
"notificationsData.content": 1,
"notificationsData.estimationId": 1,
"notificationsData._id": 1,
"notificationsData.commentId": 1,
"notificationsData.commentData.content": 1,
"notificationsData.commentData._id": 1,
leadId: 1,
projectOverview: 1
}
},
])
in the above query i get notificationData based on estimationId and commentData data based on commentId that is specified inside notificationData
so here it is solution that i do and works fine.
I would like unmatched data from the USERS collection. Here I have two collections 1) USERS, 2) COMPANY.I am able to get the matched data from both USERS using aggregate function. but in this case I want data from USERS table which are not assigned to a company.
USERS table
{
_id: "AAA",
fullName:"John Papa"
},
{
_id: "BBB",
fullName:"Robin Son"
}
COMPANY table
{
_id: "1sd1s",
Name:"Lumbar Company"
User:"AAA"
},
{
_id: "23s1dfs3",
Name:"Patricia"
User:"AAA"
}
$lookup works like LEFT OUTER JOIN so it will remove empty array when there's no match. Then you can use $size to get only empty arrays:
db.users.aggregate([
{
$lookup: {
from: "company",
localField: "_id",
foreignField: "User",
as: "companies"
}
},
{
$match: {
$expr: {
$eq: [ { "$size": "$companies" }, 0 ]
}
}
}
])
Mongo Playground
I've got an Object Mission referring to another object Position with a key _p_position.
Mission objects look like:
{
_id: "ijjn97678",
_p_position: "Position$qwerty123",
...
}
Position objects look like:
{
_id: "qwerty123",
...
}
I don't know if it is Mongo or Parse convention but as one can see a Position$ is added on relational position attribute in missions.
I'd like to aggregate both into a single Object to get a results similar to the following:
{
_id: "ijjn97678",
_p_position: "Position$qwerty123",
positions: [
{
_id: "qwerty123"
}
]
}
using:
missions.aggregate([
{
$lookup: {
as: "position",
from: "Position",
foreignField: "_id",
localField: "_p_position",
},
},
])
But I need to remove Position$ from _p_position. Is there a way I can compute "_p_position" before it is used to find a matching Position's id ?
PS: I only have reading rights on DB
You can use $addFields to add another field which will be then passed to $lookup stage. To get the part that's following the dollar sign you need: $indexOfBytes and $substr operators. Additionally dollar sign itself is a special character in Aggregation Framework (represents a field reference) so you need $literal to force it to be considered as regular field
db.missions.aggregate([
{
$addFields: {
value: {
$let: {
vars: { index: { $indexOfBytes: [ "$_p_position", { $literal: "$" } ] } },
in: { $substr: [ "$_p_position", { $add: [ "$$index", 1 ] } , { $strLenBytes: "$_p_position" } ] }
}
}
}
},
{
$lookup: {
from: "Position",
localField: "value",
foreignField: "_id",
as: "position"
}
}
])
I'm relatively new to mongodb aggregations and I have a tiny problem:
I want to make a join between two collections. The problem is, that the foreign field is placed in an inner array. That means that I have to unwind the array in order to make a proper $match. In my $match, I use an $epxr and an $eq in order to make the join on the unwinded documents (which is intended and therefor not a problem). The $expr is needed to access variables from the orginal collection:
[
...
{
$lookup: {
from: 'foreignCollection',
as: 'field',
let: {
localField: '$someComparisonField'
},
pipeline: [
{
$unwind: '$arr'
},
{
$match: {
$expr: {
$eq: [ '$arr.foreignField', '$$localField' ]
}
}
}
]
}
}
]
However field is always an empty array in my result set. I seriously don't know what I'm doing wrong :D
Can someone help me?
Edit:
As requested, some sample data for the two involved collections:
orginalCollection:
{
...
someComparisonField: 1
},
{
...
someComparisonField: 2
}
foreignCollection:
{
...
arr: [
{
...
foreignField: 1
},
{
...
foreignField: 1
},
{
...
foreignField: 2
},
]
},
{
...
arr: [
{
...
foreignField: 1
},
{
...
foreignField: 2
},
{
...
foreignField: 2
},
]
},
{
...
arr: [
{
...
foreignField: 2
},
{
...
foreignField: 1
},
{
...
foreignField: 2
},
]
},
Edit 2:
I forgot to add a small detail: with $eq in the inner pipeline, I am accessing a fixed index which means that the foreignField actually looks like this: foreignField: [ <value> ].
With some investigation, I came to the following conclusion:
Before reading further, I recommend reading both of my edits to the questions. Especially my 2nd edit.
It seems like $eq within an $expr simply can't compare a fixed index.
This expression simply doesn't work somehow:
{
$expr: {
$eq: [ '$arr.foreignField.0': '$$localField' ]
}
}
To work arround this, I created an projection before this stage which extracts the value from the desired fixed index and stores it in a new field. So now the particular stages from the inner pipeline look like this:
...
{
$project: {
value: { $arrayElemAt: [ '$arr.foreignField', 0 ] }
}
},
{
$match: {
$expr: {
$eq: [ '$value', '$$localField' ]
}
}
}
...