nodejs /Mongo - multiple finds not working - node.js

Question

Still a NooB to Node/Mongo and am stuck on this.
I have two mongo collections, Tenants and Rent. Rent collection has the tenant _id in the schema. The following function is searching through all active tenants and for each of those pulling out some attributes for the latest rent document.
The first part of the function populates the tenant object with the results. all working good.
The second .then starts to iterate through the tenant object pulling out the _id to use in the Rent query. (join).
the issue is the for loop seems to iterate through and print the _id correctly, but the second find query seems to only print out the last document in the object. I am just not sure why this is happening
thanks in advance
app.get('/chargerenttest/:date', (req,res) => {
//check date is valid
var rentChargeDate = new Date(req.params.date);
var tenant = "";
//for each active tenant
Tenant .find({
activeTenant : true
})
.then ((tenant) => {
if (!tenant) {
return res.status(404).send();
}
console.log("found tenents")
return tenant
})
.then ((tenant) => {
for (var i in tenant) {
console.log(i)
console.log(tenant[i]._id)
Rent
.find({
"paymentType" :"Rent",
"tenantID" : tenant[i]._id,
"activeEntry": true})
.limit(1)
.sort({datePaid: -1})
// sort in decending date ( latested on top)
.then ((rent) => {
lastPayment = rent[0].datePaid;
lastAmountPaid = rent[0].amountPaid;
console.log("--------",i)
console.log("tenant",tenant[i]._id)
console.log("rentamount",tenant[i].rentAmount)
console.log("lastpayment", lastPayment)
});
}
})
})

Answer 1

Your query can be simplified by running an aggregate operation that makes use of a pipeline with the $lookup operator which allows you to perform a left outer join to another collection in the same database to filter in documents from the "joined" collection for processing.
Consider running the following pipeline:
Rent.aggregate([
{
"$match": {
"paymentType": "Rent",
"activeEntry": true
}
},
{
"$lookup": {
"from": "tenants",
"localField": "tenantID",
"foreignField": "_id",
"as": "tenants"
}
},
{ "$match": { "tenants": { "$ne": [] }, "tenants.activeTenant": true } },
//{ "$unwind": "$tenants" },
{ "$sort": { "datePaid": -1 } },
{ "$limit": 1 }
]).exec((err, rent) => {
if (err) throw err;
lastPayment = rent[0].datePaid;
lastAmountPaid = rent[0].amountPaid;
tenant = rent[0].tenants[0];
console.log("tenant",tenant._id)
console.log("rentamount",tenant.rentAmount)
console.log("lastpayment", lastPayment)
});

Answer 2

This module #coolgk/mongo could make joining multiple collections a lot simpler.
Examples
SQL to Mongo Join
Left Join
SELECT * FROM a LEFT JOIN b ON a.b_id = b.id
becomes
model.find({}, {
join: [ { on: 'b_id' } ]
})
Result:
[{
_id: '5a8bde4ae2ead929f89f3c42',
a_name: 'aname1',
b_id: {
_id: '5a8bde4ae2ead929f89f3c41',
b_name: 'bname1'
}
}, { ... }, ... ]
Inner Join with Constraints
SELECT * FROM a, b WHERE a.b_id = b.id AND b.b_name = 'bname1'
becomes
model.find({}, {
join: [ { on: 'b_id', filters: { b_name: 'bname1' } } ]
})
Result:
[{
_id: '5a8bdfb05d44ea2a08fa8a4c',
a_name: 'aname2',
b_id: {
_id: '5a8bdfb05d44ea2a08fa8a4b',
b_name: 'bname2'
}
}]
Inner Join on Mulitple Collections
SELECT * FROM a, b, c WHERE a.b_id = b.id AND b.c_id = c.id AND c.c_name = 'cname3'
becomes
modela.find({}, {
join: [{
on: 'b_id',
join: [{
on: 'c_id',
filters: { c_name: 'cname3' }
}]
}]
})
Result:
[{
_id: '5a8bdfc1b07af22a12cb1f0b',
a_name: 'aname3',
b_id: {
_id: '5a8bdfc1b07af22a12cb1f0a',
b_name: 'bname3',
c_id: {
_id: '5a8bdfc1b07af22a12cb1f09',
c_name: 'cname3'
}
}
}]