MongoDB join two complex collection - mongodb

Question

I got two collections
data
{
_id: ObjectId('123'),
uuid: '123abc'
content: 'hello'
}
{
_id: ObjectId('456'),
uuid: '123abc'
content: 'hi'
}
history
{
_id: ObjectId('xxx'),
uuid: '123abc'
data: [{path: '/hello.json', objectId: '123'}, {path: '/hi.json', objectId: '456'}]
}
I want
{
_id: ObjectId('123'),
uuid: '123abc'
content: 'hello'
path: '/hello.json'
}
{
_id: ObjectId('456'),
uuid: '123abc'
content: 'hi'
path: '/hi.json'
}
Step:
use the uuid to find the second json
use the objectId of the second json data array element to locate the first json
Does anyone who knows how to write the MongoDB operations to join the two collections
the result after the second stage is finished

Answer 1

You can do it with Aggregation Framework:
$lookup - To fetch data from the history collection
$set with $first - To get the first element from the history property, since the $lookup always return an array
$set with $filter - To create a path_element property that has the filtered history based on the document _id.
$project - to project the data as expected output.
db.data.aggregate([
{
"$lookup": {
"from": "history",
"localField": "uuid",
"foreignField": "uuid",
"as": "history"
}
},
{
"$set": {
"history": {
"$first": "$history"
}
}
},
{
$set: {
path_element: {
"$filter": {
"input": "$history.data",
"cond": {
$eq: [
{
$toString: "$_id"
},
"$$this.objectId"
]
}
}
}
}
},
{
$project: {
_id: 1,
uuid: 1,
content: 1,
path: {
"$getField": {
"field": "path",
"input": {
$first: "$path_element"
}
}
}
}
}
])
Working example