How to write a $match on a $lookup document in MongoDB - mongodb

Question

I have two MongoDB collections that look like this:
Products Specials
---------- ----------
_id _id
name product_id
country zip
price percent_discount
out_of_stock
I'm using GraphQL as well so I wrote up an aggregate pipeline that returns the data in this structure:
specials {
_id
product {
_id
name
country
price
}
zip
percent_discount
out_of_stock
}
This aggregate pipeline I wrote works great and looks like this:
let response = await Specials.aggregate([
{
$lookup: {
from: 'products',
localField: 'product_id',
foreignField: '_id',
as: 'product'
}
},
{
$unwind: '$product'
},
{
$match: {
zip: zip
}
}
])
return response;
Now I'm trying to add a filter into this. The filter should match the name or country in the product collection preferably with regex. So I tried writing something like this but it's yielding over 8000 results when there should be only 2-3:
let response = await Specials.aggregate([
{
$match: { zip: zip }
},
{
$lookup: {
from: "products",
let: { product_id: "$product_id" },
pipeline: [
{
$match: {
$expr: {
$and: [
{
_id: "$$product_id"
},
{
$or: [
{
name: filter
},
{
country: filter
}
]
}
]
}
}
}
],
as: "product"
}
},
{
$unwind: "$product"
}
])

Answer 1

If you're using Mongo version 4.2+ you can use $regexMatch
let response = await Specials.aggregate([
{
$lookup: {
from: "products",
let: { product_id: "$product_id" },
pipeline: [
{
$match: {
$expr: {
$and: [
{
$eq: ["$$product_id", "$_id"]
},
{
$or: [
{
$regexMatch: { input: "$name", regex: filterRegex }
},
{
$regexMatch: { input: "$country", regex: filterRegex }
}
]
}
]
}
}
}
],
as: "product"
}
},
{
$unwind: "$product"
},
{
$match: {
$and: [
{
zip: zip
}
]
}
}
])
return response;

Answer 2

This is the following solution that I was able to get working:
let response = await Specials.aggregate([
{
$lookup: {
from: "products",
let: { product_id: "$product_id" },
pipeline: [
{
$match: {
$and: [
{
$or: [
{
name: { $regex: filter }
},
{
country: { $regex: filter }
}
]
},
{
$expr: {
$eq: ["$$product_id", "$_id"]
}
}
]
}
}
],
as: "product"
}
},
{
$unwind: "$product"
},
{
$match: {
$and: [
{
zip: zip
}
]
}
}
])
return response;
** Updated with the working $regex implementation