MongoDB retrun array of Items from other arrays, with reduced datapoints - mongodb

Question

I have a user object that looks (roughly) like the example below - a user containg Arrays of Objects for "autos" "boats" and "planes" - each object COULD have an image URL, but many do not, I want an array of ALL the image URLs form a user (regardless of which group they are in) and I want SOME but NOT ALL of the object that is associated with that image.
DATA MODEL
{
user: STRING,
autos: [
{
make: STRING,
model: STRING,
year: NUMBER,
price: NUMBER,
image: STRING
}
],
boats: [
{
make: STRING,
model: STRING,
year: NUMBER,
price: NUMBER,
image: STRING
}
],
planes: [
{
make: STRING,
model: STRING,
year: NUMBER,
price: NUMBER,
image: STRING
}
]
}
This is a reduced "object" in each of these arrays, the real data contains many points that are specific to each of these TYPES, and I cannot change the model at this point.
So I am able to pull back an array of Image URLs from the arrays, and concat them into a single array, But then I just have URLS... what I want is the "make" and "model" and "image URL" for each
Here is the Query I've got
query = [
{
$match: matchCriteria
},
{
$project: {
_id: 0,
image: {
$filter: {
input: {
$concatArrays: [
'$autos.image',
'$boats.image',
'$planes.image'
]
},
cond: {
$and: [ // skip records without image data
{ $eq: [{ $type: "$$this" }, "string"] },
{ $ne: ["$$this", ""] }
]
}
}
}
}
}
];
this gives me data looking like this
"data": [
"https://www.yourPics.com/see?image=image4",
"https://www.yourPics.com/see?image=image5",
"https://www.yourPics.com/see?image=image6",
"https://www.yourPics.com/see?image=image1",
"https://www.yourPics.com/see?image=image2",
"https://www.yourPics.com/see?image=image3",
"https://www.yourPics.com/see?image=image7",
"https://www.yourPics.com/see?image=image8",
"https://www.yourPics.com/see?image=image9",
"https://www.yourPics.com/see?image=image10",
"https://www.yourPics.com/see?image=image11"
],
But I WANT something that looks like this
"data": [
{
make:"some make4",
model:"some model4",
image: "https://www.yourPics.com/see?image=image4"
},
{
make:"some make5",
model:"some model5",
image: "https://www.yourPics.com/see?image=image5"
},
{
make:"some make6",
model:"some model6",
image: "https://www.yourPics.com/see?image=image6"
},
...
],
Any help is greatly appreciated.

Answer 1

I'm not sure why you're concating just the image attribute of those objects. Doing that, you will certainly end up with just an array of images. Why not concat the entire arrays? As in:
$concatArrays: ["$autos", "$boats"]
So I have put this Playground together for you. Using this project:
{
$project: {
items: {
$filter: {
input: {
$concatArrays: [
"$autos",
"$boats"
]
},
as: "items",
cond: {
$and: [
{
$ne: [
"$$items.image",
undefined
]
},
{
$ne: [
"$$items.image",
""
]
}
]
}
}
}
}
}
You will get this result:
[
{
"_id": ObjectId("5a934e000102030405000000"),
"items": [
{
"image": "https://pont.com",
"make": "Pontiac",
"model": "Sunfire",
"year": "2004"
},
{
"image": "https://aluma.com",
"make": "Aluma",
"model": "X4",
"price": "100,000",
"year": "2021"
}
]
}
]
From here, excluding the keys you don't want (e.g year, price) is a trivial matter. Just project only what you want:
{
$project: {
_id: 0,
"items.make": 1,
"items.model": 1,
"items.image": 1
}
}
Playground: https://mongoplayground.net/p/qFIwLhuXR84