Aggregate document multilevel - node.js

Question

Now consider the case , i have one document containing below collection like structure.
Below is the order collection
{
"_id" : ObjectId("5788fcd1d8159c2366dd5d93"),
"color" : "Blue",
"code" : "1",
"category_id" : ObjectId("5693d170a2191f9020b8c815"),
"description" : "julia tried",
"name" : "Order1",
"brand_id" : ObjectId("5b0e52f058b8287a446f9f05")
}
There is also a collection for Brand and Category. This is the
Category collection
{
"_id" : ObjectId("5693d170a2191f9020b8c815"),
"name" : "Category1",
"created_at" : ISODate("2016-01-11T20:32:17.832+0000"),
"updated_at" : ISODate("2016-01-11T20:32:17.832+0000"),
}
Brand Collection
{
"_id" : ObjectId("5b0e52f058b8287a446f9f05"),
"name" : "brand1",
"description" : "brand1",
"updated_at" : ISODate("2017-07-05T09:18:13.951+0000"),
"created_at" : ISODate("2017-07-05T09:18:13.951+0000"),
}
Now after aggregation applied, it should result in below format:
{
'brands': [
{
_id: '*******'
name: 'brand1',
categories: [
{
_id: '*****',
name: 'category_name1',
orders: [
{
_id: '*****',
title: 'order1'
}
]
}
]
}
]
}

Answer 1

You can try below aggregation:
db.brand.aggregate([
{
$lookup: {
from: "order",
localField: "_id",
foreignField: "brand_id",
as: "orders"
}
},
{
$unwind: "$orders"
},
{
$lookup: {
from: "category",
localField: "orders.category_id",
foreignField: "_id",
as: "categories"
}
},
{
$unwind: "$categories"
},
{
$group: {
_id: "$_id",
name: { $first: "$name" },
description: { $first: "$description" },
updated_at: { $first: "$updated_at" },
created_at: { $first: "$created_at" },
categories: { $addToSet: "$categories" },
orders: { $addToSet: "$orders" }
}
},
{
$addFields: {
categories: {
$map: {
input: "$categories",
as: "category",
in: {
$mergeObjects: [
"$$category", {
orders: [ {
$filter: {
input: "$orders",
as: "order",
cond: { $eq: [ "$$category._id", "$$order.category_id" ] }
}
} ]
} ]
}
}
}
}
},
{
$project: {
orders: 0
}
}
])
Basically you have to use $lookup twice to "merge" data from all these collections based on brand_id and category_id fields. Since you expect orders in categories in brands you can use $unwind for both arrays and then use $group to get following shape:
{
"_id" : ObjectId("5b0e52f058b8287a446f9f05"),
"name" : "brand1",
"description" : "brand1",
"updated_at" : ISODate("2017-07-05T09:18:13.951Z"),
"created_at" : ISODate("2017-07-05T09:18:13.951Z"),
"categories" : [
{
"_id" : ObjectId("5693d170a2191f9020b8c814"),
"name" : "Category1",
"created_at" : ISODate("2016-01-11T20:32:17.832Z"),
"updated_at" : ISODate("2016-01-11T20:32:17.832Z")
}
],
"orders" : [
{
"_id" : ObjectId("5788fcd1d8159c2366dd5d93"),
"color" : "Blue",
"code" : "1",
"category_id" : ObjectId("5693d170a2191f9020b8c814"),
"description" : "julia tried",
"name" : "Order1",
"brand_id" : ObjectId("5b0e52f058b8287a446f9f05")
}
]
}
Now you have brand1 with all its subcategories and all orders that should be placed in one of those categories. The only thing is how to "nest" orders in categories. One way to do that might be $map where you can merge each category with all orders that match that category (using $mergeObjects you don't have to specify all properties from categories object).
To match category with orders you can perform $filter on orders array.
Then you can drop orders since those are nested into categories so you don't need them anymore.
EDIT: 3.4 version
In MongoDB 3.4 you can't use $mergeObjects so you should specify all properties for `categories:
db.brand.aggregate([
{
$lookup: {
from: "order",
localField: "_id",
foreignField: "brand_id",
as: "orders"
}
},
{
$unwind: "$orders"
},
{
$lookup: {
from: "category",
localField: "orders.category_id",
foreignField: "_id",
as: "categories"
}
},
{
$unwind: "$categories"
},
{
$group: {
_id: "$_id",
name: { $first: "$name" },
description: { $first: "$description" },
updated_at: { $first: "$updated_at" },
created_at: { $first: "$created_at" },
categories: { $addToSet: "$categories" },
orders: { $addToSet: "$orders" }
}
},
{
$addFields: {
categories: {
$map: {
input: "$categories",
as: "category",
in: {
_id: "$$category._id",
name: "$$category.name",
created_at: "$$category.created_at",
updated_at: "$$category.updated_at",
orders: [
{
$filter: {
input: "$orders",
as: "order",
cond: { $eq: [ "$$category._id", "$$order.category_id" ] }
}
}
]
}
}
}
}
},
{
$project: {
orders: 0
}
}
])