Use $ and $elemMatch to group entities - mongodb

Question

Considering the following document in my mongo DB instance :
{
"_id": 1,
"people": [
{"id": 1, "name": "foo"},
{"id": 2, "name": "bar"},
/.../
],
"stats": [
{"peopleId": 1, "workHours": 24},
{"peopleId": 2, "workHours": 36},
/.../
}
Each element in my collection represent the work of every employee in my company, each weeks. As an important note, peopleId may change from one week to another !
I would like to get all weeks where foo worked more than 24 hours. As you can see, the format is kinda annoying since the people name and the work hours are separated in my database. A simple $and is not enough.
I wonder if, using some $ and $elemMatch I can achieve doing this query.
Can I use this to group the "people" entities with "stats" entities ?

Answer 1

Query to get foo worked more than 24 hours.
db.collection.aggregate([
{$unwind: { path : "$people"}},
{$unwind: { path : "$stats"}},
{$match: { "people.name" : "foo"}},
{$group: {
_id: "$_id",
peopleIdMoreThan24: { $addToSet: {
$cond : { if : { $and : [ {"$eq" : ["$people.id", "$stats.peopleId" ] },
{"$gt" : ["$stats.workHours", 24] }]} , then : "$people.id", else: "Not satisfying the condition"}}}
}
},
{$unwind: { path : "$peopleIdMoreThan24" }},
{$match: { "peopleIdMoreThan24" : {$nin : [ "Not satisfying the condition"]}}},
]);
Data in collection:-
/* 1 */
{
"_id" : 1,
"people" : [
{
"id" : 1,
"name" : "foo"
},
{
"id" : 2,
"name" : "bar"
}
],
"stats" : [
{
"peopleId" : 1,
"workHours" : 24
},
{
"peopleId" : 2,
"workHours" : 36
}
]
}
/* 2 */
{
"_id" : 2,
"people" : [
{
"id" : 1,
"name" : "foo"
},
{
"id" : 2,
"name" : "bar"
}
],
"stats" : [
{
"peopleId" : 1,
"workHours" : 25
},
{
"peopleId" : 2,
"workHours" : 36
}
]
}
/* 3 */
{
"_id" : 3,
"people" : [
{
"id" : 1,
"name" : "foo"
},
{
"id" : 2,
"name" : "bar"
}
],
"stats" : [
{
"peopleId" : 1,
"workHours" : 25
},
{
"peopleId" : 2,
"workHours" : 36
}
]
}
Output:-
The output has document id and people id of foo worked more than 24 hours.
/* 1 */
{
"_id" : 3,
"peopleIdMoreThan24" : 1
}
/* 2 */
{
"_id" : 2,
"peopleIdMoreThan24" : 1
}