MongoDB Aggregation function - mongodb

Question

I have the following JSON Documents in Mongo collection named "Movies"
{
"_id": "5ed0c9700b9e8b0e2c542054",
"movie_name": "Jake 123",
"score": 20,
"director": "Jake"
},
{
"_id": "5ed0a9840b9e8b0e2c542053",
"movie_name": "Avatar",
"director": "James Cameroon",
"score": 50,
"boxoffice": [
{
"territory": "US",
"gross": 2000
},
{
"territory": "UK",
"gross": 1000
}
]
},
{
"_id": "5ed0a9630b9e8b0e2c542052",
"movie_name": "Titanic",
"score": 100,
"director": "James Cameroon",
"boxoffice": [
{
"territory": "US",
"gross": 1000
},
{
"territory": "UK",
"gross": 500
}
],
"actors": [
"Kate Winselet",
"Leonardo De Caprio",
"Rajinikanth",
"Kamalhaasan"
]
}
I run the below query which finds the maximum collection of a country of various movies. My intention is to find the maximum collection and the corresponding territory.
db.movies.aggregate([
{$match: {"boxoffice" : { $exists: true, $ne : []}}},
{$project: {
"title":"$movie_name", "max_boxoffice": {$max : "$boxoffice.gross"},
"territory" : "$boxoffice.territory" } }
])
I get the result as follows. How do I get the correct territory that corresponds to the collection?
{
"_id" : ObjectId("5ed0a9630b9e8b0e2c542052"),
"title" : "Titanic",
"max_boxoffice" : 1000,
"territory" : [
"US",
"UK"
]
},
{
"_id" : ObjectId("5ed0a9840b9e8b0e2c542053"),
"title" : "Avatar",
"max_boxoffice" : 2000,
"territory" : [
"US",
"UK"
]
}
Expected output:
Avatar and Titanic has collected more money in US. I wanted territories to display the values of them
{
"_id" : ObjectId("5ed0a9630b9e8b0e2c542052"),
"title" : "Titanic",
"max_boxoffice" : 1000,
"territory" : "US"
},
{
"_id" : ObjectId("5ed0a9840b9e8b0e2c542053"),
"title" : "Avatar",
"max_boxoffice" : 2000,
"territory" : "US"
}

Answer 1

For this specific requirement, you can use $set (aggregation). $set appends new fields to existing documents. and we can include one or more $set stages in an aggregation operation to achieve this like:
db.movies.aggregate([
{
$match: { "boxoffice": { $exists: true, $ne: [] } }
},
{
$set: {
boxoffice: {
$filter: {
input: "$boxoffice",
cond: { $eq: ["$$this.gross", { $max: "$boxoffice.gross" }]}
}
}
}
},
{
$set: {
boxoffice: { $arrayElemAt: ["$boxoffice", 0] }
}
},
{
$project: {
"title": "$movie_name",
"max_boxoffice": "$boxoffice.gross",
"territory": "$boxoffice.territory"
}
}
])
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