MongoDB - Mongoose : Aggregate generation, $match $group $project - node.js

Question

I'm newbie in the mongoDB world. I'm developping a website on nodeJS with expressJS and mongoose as DB.
I'm studying graphic orientation and I am generated a DB with this modele
:
var userSchema = new Schema({
profile:{
sexe: String, // ('male' or 'female')
age: String, // ('kid', 'adult', 'old')
rank: String, // ('low', 'middle', 'high')
},
design:{
luminosity: String, // ('light', 'dark')
color: String, // ('blue', 'green', 'pink', 'orange')
shape: String, // ('rounded', 'squared')
font: String, // ('serif', 'sans serif')
}
});
On different page, I want to display some statistics, for exemple, on the page luminosity, where user chooses between light or dark. I want to display him what people mostly pick.
For example, with the section sexe : what mostly pick female (68% of them choose light, for example).
I think the best way to get all the numbers to create the statistics is to use aggregate.
As newbie, it destroys my mind to generate the perfect query, I am really lost in this framework !
Would love your advice !

Answer 1

Your aggregation operation will be dependant on the $cond operator in the $group pipeline step to evaluate the counts based on the page luminosity and/or page color. Use the $sum accumulator operator to return the sum on each evaluated group, something like the following:
var pipeline = [
{
"$group": {
"_id": "$profile.sexe",
"light_count": {
"$sum": {
"$cond": [ { "$eq": [ "$design.luminosity", "light" ] }, 1, 0 ]
}
},
"dark_count": {
"$sum": {
"$cond": [ { "$eq": [ "$design.luminosity", "dark" ] }, 1, 0 ]
}
},
"blue_count": {
"$sum": {
"$cond": [ { "$eq": [ "$design.color", "blue" ] }, 1, 0 ]
}
},
"green_count": {
"$sum": {
"$cond": [ { "$eq": [ "$design.color", "green" ] }, 1, 0 ]
}
},
"pink_count": {
"$sum": {
"$cond": [ { "$eq": [ "$design.color", "pink" ] }, 1, 0 ]
}
},
"orange_count": {
"$sum": {
"$cond": [ { "$eq": [ "$design.color", "orange" ] }, 1, 0 ]
}
}
}
},
{
"$project": {
"_id": 0, "gender": "$_id",
"luminosity": {
"light": "$light_count",
"dark": "$dark_count"
},
"color": {
"blue": "$blue_count",
"green": "$green_count",
"pink": "$pink_count",
"orange": "$orange_count"
}
}
}
];
User.aggregate(pipeline)
.exec(function (err, result){
// handle error
if (err) throw Error;
console.log(result);
})