How to use aggregate in mongoosejs with this example - node.js

Question

I am here to ask a question about mongo aggregate function to achieve this example.
Scenario
I have 3 Mongo Schema i.e House, family and educations which as :
House: {
_id: ObjectId,
state: Number,
houseNumber: Number
}
Family: {
_id: ObjectId,
houseId: ObjectId,//ref: house
name: String,
gender: String
}
Education: {
_id: ObjectId,
familyId: ObjectId,//ref: Family
level: String, //might be one of ["primary","secondary","higher_secondary"]
}
Expected Output:
{
state1: {
primary: {
male: 3,
female: 4
},
secondary: {
male: 4,
female: 8
}
},
state2: {
primary: {
male: 5,
female: 4
},
secondary: {
male: 4,
female: 6
}
}
}
I want to group all the education level by gender and then ward.
What I did:
I am newbie in mongo world and recently shifted from sql to no-sql. I had done this:
let edu = await Education.find({level: "primary"}).populate({
path: "family",
match: {gender: "male"},
select: "house",
populate: {
path: "house",
match: {state: 1},
select: "_id"
}
});
let count = (await edu.filter(each => !isEmpty(each.family) && !isEmpty(each.family.house)).length) || 0;
By doing this I get count of male member who has studied primary from state 1. but I cannot afford to call this function one by one for each data.
As requestd the sample data are:
house = [
{
_id: AA1,
state: 1,
houseNumber: 101
},
{
_id: AA2,
state: 1,
houseNumber: 102
},
{
_id: AA3,
state: 2,
houseNumber: 201
}
];
family = [
{
_id: BB1,
houseId: AA1, //ref: house
name: "John",
gender: "male"
},
{
_id: BB2,
houseId: AA1, //ref: house
name: "Solena",
gender: "female"
},
{
_id: BB3,
houseId: AA2, //ref: house
name: "Efrain",
gender: "male"
},
{
_id: BB4,
houseId: AA3, //ref: house
name: "Naruto",
gender: "male"
}
];
education = [
{
_id: CC1,
familyId: AA1, //ref: Family
level: "primary"
},
{
_id: CC2,
familyId: AA2, //ref: Family
level: "secondary"
},
{
_id: CC3,
familyId: AA3, //ref: Family
level: "primary"
},
{
_id: CC4,
familyId: AA4, //ref: Family
level: "secondary"
}
];
P.S expected output is not relevant output to the sample data. And ObjectId has been replaced with some unique reference.
Any lead from here guyz?

Answer 1

You can use below aggregation query in 4.x version.
Query the family collection and join to education collection to get the level followed by join to house collection to get the state.
Once you have all the data group by state, level and gender to count all the matches followed by other groups for formatting result. Last stage to promote the aggregated result into its own document.
Last two groups formatting the results from previous stage into named key value document. First group to format the results into gender and count grouped by state. Second group to format the previously combined gender and count with education key.
Finally replace root stage to format the combined gender, count and education doc with state key.
Also added output after each stage for clarity.
db.family.aggregate(
[
{"$lookup":{
"from":"education",
"localField":"_id",
"foreignField":"familyId",
"as":"education"
}},
{"$unwind":"$education"},
{"$lookup":{
"from":"house",
"localField":"houseId",
"foreignField":"_id",
"as":"state"
}},
{"$unwind":"$state"},
{"$group":{
"_id":{
"state":"$state.state",
"education":"$education.level",
"gender":"$gender"
},
"count":{"$sum":1}
}},//{"_id":{"state" :1,"education" :"secondary","gender":"female"},"count":1}
{"$group":{
"_id":{"state":"$_id.state","education":"$_id.education"},
"gandc":{"$mergeObjects":{"$arrayToObject":[[["$_id.gender","$count"]]]}}
}},//{"_id":{"state":1,"education":"primary"},"gandc":{"male":2}}
{"$group":{
"_id":"$_id.state",
"egandc":{"$mergeObjects":{"$arrayToObject":[[["$_id.education","$gandc"]]]}}
}},//{"_id":1,"egandc":{"primary":{"male":2},"secondary":{"female":1}}}
{"$replaceRoot":{"newRoot":{"$arrayToObject":[[[{"$toString":"$_id"},"$egandc"]]]}}} ])
])
//{"1":{"primary":{"male" : 2 },"secondary":{"female":1}}}