Filter query for fetching product based on categories in MERN application? - mongodb

Question

This is my Product Schema
const product = mongoose.Schema({
name: {
type: String,
},
category:{
type: ObjectId,
ref: Category
}
}
I want to return the product based on filters coming from the front end.
For example: Lets consider there are 2 categories Summer and Winter. When the user wants to filter product by Summer Category an api call would me made to http://localhost:8000/api/products?category=summer
Now my question is, how do I filter because from the frontend I am getting category name and there is ObjectId in Product Schema.
My attempt:
Project.find({category:categoryName})

Answer 1

If I've understood correctly you can try one of these queries:
First one is using pipeline into $lookup to match by category and name in one stage like this:
yourModel.aggregate([
{
"$lookup": {
"from": "category",
"let": {
"category": "$category",
},
"pipeline": [
{
"$match": {
"$expr": {
"$and": [
{
"$eq": [
"$id",
"$$category"
]
},
{
"$eq": [
"$name",
"Summer"
]
}
]
}
}
}
],
"as": "categories"
}
},
{
"$match": {
"categories": {
"$ne": []
}
}
}
])
Example here
Other way is using normal $lookup and then $filter the array returned by join.
yourModel.aggregate([
{
"$lookup": {
"from": "category",
"localField": "category",
"foreignField": "id",
"as": "categories"
}
},
{
"$match": {
"categories": {
"$ne": []
}
}
},
{
"$set": {
"categories": {
"$filter": {
"input": "$categories",
"as": "c",
"cond": {
"$eq": [
"$$c.name",
"Summer"
]
}
}
}
}
}
])
Example here
Note how both queries uses $match: { categories: { $ne : []}}, this is because if the lookup doesn't find any result it returns an empty array. By the way, this stage is optional.
Also you can add $unwind or $arrayElemAt index 0 or whatever to get only one value from the array.
Also, to do it in mongoose you only need to replace "Summer" with your variable.