Multi tool use

Clash Royale CLAN TAG

Mongodb: reverse document tree as a view (using C# driver)

I'm trying the following (simplistic scenario):

I have two documents that look like this (cinema has timeslots, timeslot has a movie):

{
"_id":"5b5dd8932dc7aa1e180f8c23",
"Name":"Cinema 1",
"TimeSlots":[
{
"Start":"2018-07-29T16:00:00.000Z",
"End":"2018-07-29T18:30:00.000Z",
"Movie":{
"_id":"5b5dd8932dc7aa1e180f8c24",
"Name":"Movie 1"
}
},
{
"Start":"2018-07-29T15:00:00.000Z",
"End":"2018-07-29T17:15:00.000Z",
"Movie":{
"_id":"5b5dd8932dc7aa1e180f8c25",
"Name":"Movie 2"
}
}
]
}

{
"_id":"5b5dd8932dc7aa1e180f8c26",
"Name":"Cinema 2",
"TimeSlots":[
{
"Start":"2018-07-29T18:00:00.000Z",
"End":"2018-07-29T20:30:00.000Z",
"Movie":{
"_id":"5b5dd8932dc7aa1e180f8c24",
"Name":"Movie 1"
}
},
{
"Start":"2018-07-29T19:00:00.000Z",
"End":"2018-07-29T21:15:00.000Z",
"Movie":{
"_id":"5b5dd8932dc7aa1e180f8c25",
"Name":"Movie 2"
}
}
]
}


I'd like to reverse the tree structure (so I have movies that have timeslots, which are linked to cinemas). In C# using LINQ I would do the following:

var movies = cinemas
.SelectMany(cinema => cinema.TimeSlots)
.Select(timeSlot => timeSlot.Movie)
.Distinct(new MovieEqualityComparer())
.Select(movie =>
{
movie.TimeSlots = cinemas
.SelectMany(cinema => cinema.TimeSlots)
.Where(timeSlot => timeSlot.Movie.Id == movie.Id)
.ToList();

return movie;
})
.ToList();


I'm wondering how one would achive this using the aggregate functions and a aggregate pipeline. I've tried several options including $project, $unwind and $group but I don't seem to be able to achieve the result I want. Any help is appriciated.

$project

$unwind

$group

This is what I have so far:

[
{
$unwind:{ path:'$TimeSlots' }
},
{
$unwind:{ path:'$TimeSlots.Movie' }
},
{
$group:{
_id:'$TimeSlots.Movie._id',
movies:{ $addToSet:'$TimeSlots.Movie' } }
},
{ $project: { movieId: '$_id'} } }
]


Which results into a similar result of my LINQ query up until the distinct.

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