MongoDB Lookup values based on dynamic field name - mongodb-query

Question

I'm pretty sure the below can be done, I'm struggling to understand how to do it in MongoDB.
My data is structured like this (demo data):
db={
"recipes": [
{
"id": 1,
"name": "flatbread pizza",
"ingredients": {
"1010": 1,
"1020": 2,
"1030": 200
}
},
{
"id": 2,
"name": "cheese sandwich",
"ingredients": {
"1040": 1,
"1050": 2
}
}
],
"ingredients": [
{
"id": 1010,
"name": "flatbread",
"unit": "pieces"
},
{
"id": 1020,
"name": "garlic",
"unit": "clove"
},
{
"id": 1030,
"name": "tomato sauce",
"unit": "ml"
},
{
"id": 1040,
"name": "bread",
"unit": "slices"
},
{
"id": 1050,
"name": "cheese",
"unit": "slices"
}
]
}
The output I'm trying to achieve would look like this:
[
{
"id": 1,
"name": "flatbread pizza",
“flatbread”: “1 pieces”,
“garlic”: “2 cloves”,
“tomato sauce”: “200 ml”
},
{
"id": 2,
"name": "cheese sandwich",
“bread”: “1 slices”,
“cheese”: “2 slices”
}
]
I've tried several approaches, and I get stuck at the bit where I need to do a lookup based on the ingredient name (which actually is the id). I tried using $objectToArray to turn it into a k-v document, but then I get stuck in how to construct the lookup pipeline.

Answer 1

This is not a simple solution, and probably can be improved:
db.recipes.aggregate([
{
"$addFields": {
ingredientsParts: {
"$objectToArray": "$ingredients"
}
}
},
{
$unwind: "$ingredientsParts"
},
{
"$group": {
_id: "$id",
name: {
$first: "$name"
},
ingredientsParts: {
$push: {
v: "$ingredientsParts.v",
id: {
$toInt: "$ingredientsParts.k"
}
}
}
}
},
{
"$lookup": {
"from": "ingredients",
"localField": "ingredientsParts.id",
"foreignField": "id",
"as": "ingredients"
}
},
{
$unwind: "$ingredients"
},
{
"$addFields": {
"ingredientsPart": {
"$filter": {
input: "$ingredientsParts",
as: "item",
cond: {
$eq: [
"$$item.id",
"$ingredients.id"
]
}
}
}
}
},
{
$project: {
ingredients: 1,
ingredientsPart: {
"$arrayElemAt": [
"$ingredientsPart",
0
]
},
name: 1
}
},
{
"$addFields": {
units: {
k: "$ingredients.name",
v: {
"$concat": [
{
$toString: "$ingredientsPart.v"
},
" ",
"$ingredients.unit"
]
}
}
}
},
{
$group: {
_id: "$_id",
name: {
$first: "$name"
},
units: {
$push: "$units"
}
}
},
{
"$addFields": {
"data": {
"$arrayToObject": "$units"
}
}
},
{
"$addFields": {
"data.id": "$_id",
"data.name": "$name"
}
},
{
"$replaceRoot": {
"newRoot": "$data"
}
}
])
You can see it works here
As rickhg12hs said, it can be modeled better.