How to apply $lookup with conditions in mongodb? - mongodb

Question

I am using mongodb databases and want to apply $lookup on 2 collections but with specific conditions.
I have one collection named Company like this
new Schema({
name: String,
benefit: String,
benefitDesc: String,
company_url: String,
logoUrl: String,
coverUrl: String,
desc: String,
createdAt: String,
categoryId: { type: Schema.Types.ObjectId, ref: 'categories' },
})
And another collection named Referrallinks like this
new Schema({
referral_link: String,
referral_code: String,
isLink: Number,
offer_name: String,
offer_desc: String,
user_email: String,
companyId: { type: Schema.Types.ObjectId, ref: 'companies' },
addedByAdmin: { type: Boolean, default: true },
number_of_clicks: Number,
referral_country: String,
link_status: String,
categoryId: { type: Schema.Types.ObjectId, ref: 'categories' },
number_of_clicks: { type: Number, default: 0 },
createdAt: String,
updatedAt: String,
userId: { type: Schema.Types.ObjectId, ref: 'users' }
})
Now when i apply this $lookup
Company.aggregate([{
$lookup: {
from: 'referrallinks',
localField: '_id',
foreignField: 'companyId',
as: 'referrals'
}
}])
So i am getting all companies with referrals as array like this
[
{name : '', benefit : '', benefiDesc : '', referrals : []},
{name : '', benefit : '', benefiDesc : '', referrals : []},
{name : '', benefit : '', benefiDesc : '', referrals : []},
.....
]
But i want to have only referrals in each company's referrals array that have link_status value Approved.
**Note : ** I also want to have category object with company and tried this aggregation but it gives error
{
from: "referrallinks",
let: { company_id: "$_id" },
pipeline: [{
$match: {
$expr: {
$and: [
{ $eq: [ "$$company_id", "$companyId" ] },
{ $eq: [ "$link_status", "Approved" ] }
]
}
},
{
$lookup : {
from : "categories",
let : {"category_id" : "$categoryId"},
pipeline : [
{
$match : {
$expr : {
$eq : ["category_id","$_id"]
}
}
}
],
as : "company"
}
}
}],
as: "referrals"
}
How can i achieve this?

Answer 1

Use $lookup with custom pipeline to specify additional filtering condition:
Company.aggregate([{
$lookup: {
from: "referrallinks",
let: { company_id: "$_id" },
pipeline: [{
$match: {
$expr: {
$and: [
{ $eq: [ "$$company_id", "$companyId" ] },
{ $eq: [ "$link_status", "Approved" ] }
]
}
}
}],
as: "referrals"
}
}])
EDIT: to run nested $lookup your code should look like below:
Company.aggregate([{
$lookup: {
from: "referrallinks",
let: { company_id: "$_id" },
pipeline: [
{
$match: {
$expr: {
$and: [
{ $eq: [ "$$company_id", "$companyId" ] },
{ $eq: [ "$link_status", "Approved" ] }
]
}
}
},
{
$lookup: {
from: "categories",
localField: "categoryId",
foreignField: "_id",
as: "company"
}
}
],
as: "referrals"
}
}])