mognodb aggregation group by actor - mongodb

Question

I have the following film collection structure:
{
"_id" : ObjectId,
"title" : "movie-1",
"actors" : [
"actor-1",
"actor-2",
"actor-3",
],
"categories" : [
"category-1",
"category-2"
]
}
I want to display result of all actors with associate movies and categories as like as given below:
{
"actor": "actor-1",
"result": {
"category-1": [ "movie-1", "movie-2" ],
"category-2": [ "movie-1", "movie-4" ]
}
}
I have tried aggregation as like as given below:
db.film.aggregate([
{ $unwind: "$actors" },
{ $group: {
_id: "$actors",
data: { $push: { movie: "$title", categories: "$categories" } }
}
},
{
$project: {
_id: 0,
actor: "$_id",
result: {
$reduce: {
input: "$data",
initialValue: {},
in: {
$let: {
vars: { movie: "$$this.movie", categories: "$$this.categories" },
in: {
$arrayToObject: {
$map: {
input: "$$categories",
in: { k: "$$this", v: "$$movie" }
}
}
}
}
}
}
}
}
}
])
But I get all actors list with only one movie with category as like as given below:
{
"actor" : "actor-1",
"result" : {
"category-1" : "movie-1",
"category-2" : "movie-2",
"category-3" : "movie-3"
}
}
How can I solve this problem? Thanks in advance.

Answer 1

You may need to do another $unwind on the categories array after flattening the actors array then group all the flattened docs by the two fields i.e. actor and category fields to create the movie titles list.
Another group to shape the result field is required.
The following pipeline should give you the desired result:
db.film.aggregate([
{ "$unwind": "$actors" },
{ "$unwind": "$categories" },
{ "$group": {
"_id": { "actor": "$actors", "category": "$categories" },
"movies": { "$push": "$title" }
} },
{ "$group": {
"_id": "$_id.actor",
"result": {
"$push": {
"k": "$_id.category",
"v": "$movies"
}
}
} },
{ "$addFields": {
"result": { "$arrayToObject": "$result" }
} }
])

Answer 2

I've used a sledgehammer to crack a nut (c)
Some stages could be replaced by $reduce, done inside $project stage (criticism and suggestions will be welcome)
db.film.aggregate([
{
$unwind: "$actors"
},
{
$group: {
_id: "$actors",
data: {
$push: {
movie: "$title",
categories: "$categories"
}
}
}
},
{
$unwind: "$data"
},
{
$unwind: "$data.categories"
},
{
$group: {
_id: {
actors: "$_id",
categories: "$data.categories"
},
movies: {
$push: "$data.movie"
}
}
},
{
$project: {
_id: 0,
actor: "$_id.actors",
result: {
k: "$_id.categories",
v: "$movies"
}
}
},
{
$group: {
_id: "$actor",
result: {
$push: "$result"
}
}
},
{
$project: {
_id: 0,
actor: "$_id",
result: {
$arrayToObject: "$result"
}
}
},
{
$sort: {
actor: 1
}
}
])
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