aggregation.txt

# Example for finding user preferred ratings
db.ratings.aggregate([ 
    { 
        $match: {
            "_id.user_id": ObjectId("5e7a74ceea26cb1fcf0e5d71")
        }
    }, 
    { 
        $lookup: { 
            from: "movies", 
            localField: "_id.movie_id", 
            foreignField: "_id", 
            as: "movies"
        }
    }, 
    {
        $project: {
            "rating": 1,
            "movies._id": 1,
            "movies.directors": 1
        }
    },
    { 
        $unwind: "$movies"
    }, 
    { 
        $unwind: "$movies.directors"
    }, 
    { 
        $group: { 
            _id: "$movies.directors.id", 
            name: {
                $first: "$movies.directors.name"
            },
            rating: {
                $avg : "$rating"
            }
        }
    }, 
    {
        $sort: {
            rating: -1
        }
    }, 
    {
        $limit: 3
    }
])