Node.js : How to return Object in Query Aggregation?
In my case it return the data like follow
[
{
_id: 5e5e43b356602513c00a41aa,
name: 'example',
email: '[email protected]',
gender: 'male',
hobbies: 'sing,guitarplay',
countryid: 5e4bc85ec0b157304fbd7c50,
cityid: 5e55faa52d138807addca5b7,
date: 2020-03-03T11:46:59.119Z,
cityinfo: [ [Object] ],
statesinfo: [ [Object] ],
countryinfo: [ [Object] ]
}
]
and my code is as follow
router.get('/', ensureAuthenticated, (req, res) => {
Student.aggregate([
{
$lookup: {
from: "cities",
localField: "cityid",
foreignField: "_id",
as: "cityinfo",
}
},
{
$lookup:{
from: 'states',
localField: 'stateid',
foreignField: '_id',
as: 'statesinfo'
}
},
{
$lookup: {
from: "countries",
localField: "countryid",
foreignField: "_id",
as: "countryinfo",
}
},
{
"$project": {
"stateid": 0,
"__v": 0,
"countryinfo._id": 0,
"countryinfo.__v": 0,
"countryinfo.date": 0,
"statesinfo._id": 0,
"statesinfo.date": 0,
"statesinfo.__v": 0,
"statesinfo.countryid": 0,
"cityinfo._id": 0,
"cityinfo.__v": 0,
"cityinfo.date": 0,
"cityinfo.stateid": 0,
}
}
]).then(studentList => {
console.log(studentList);
});
});
so after that i just change my code with following code like follow
router.get('/', ensureAuthenticated, (req, res) => {
Student.aggregate([
{
$lookup: {
from: "cities",
localField: "cityid",
foreignField: "_id",
as: "cityinfo",
}
},
{
$lookup:{
from: 'states',
localField: 'stateid',
foreignField: '_id',
as: 'statesinfo'
}
},
{
$lookup: {
from: "countries",
localField: "countryid",
foreignField: "_id",
as: "countryinfo",
}
},
{
$unwind: "$cityinfo",
},
{
$unwind: "$statesinfo",
},
{
$unwind: "$countryinfo",
},
{
"$project": {
"stateid": 0,
"__v": 0,
"countryinfo._id": 0,
"countryinfo.__v": 0,
"countryinfo.date": 0,
"statesinfo._id": 0,
"statesinfo.date": 0,
"statesinfo.__v": 0,
"statesinfo.countryid": 0,
"cityinfo._id": 0,
"cityinfo.__v": 0,
"cityinfo.date": 0,
"cityinfo.stateid": 0,
}
}
]).then(studentList => {
console.log(studentList);
});
});
now it produce following output
[
{ _id: 5e5e494e3823c216a2c7ab01,
name: 'example',
email: '[email protected]',
gender: 'male',
hobbies: 'sing,guitarplay,cricket',
countryid: 5e4bc85ec0b157304fbd7c50,
cityid: 5e55faa52d138807addca5b7,
date: 2020-03-03T12:10:54.654Z,
cityinfo: { cityname: 'Nathdwara' },
statesinfo: { statename: 'Rajasthan' },
countryinfo: { countryname: 'India' }
}
]
hope it works..
var url = "mongodb://127.0.0.1:27017/";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
var dbo = db.db("progettotestesi12");
dbo.collection('lavoros').aggregate([{
$lookup: {
from: 'tempiobbiettivos',
localField: 'codicearticolo',
foreignField: 'cod_prodotto_su_cdl',
as: 'collegamentotempiobbiettivo'
}
}]).toArray(function(err, result) {
if (err) throw err;
console.log(result[0].collegamentotempiobbiettivo[0].cdl);
res.render('pannello/testdiroman', {
showrisultati: result,
});
});
});
i had the same problem as you can see from the picture, my object was {[]} instead of {}. i managed to return the variable using my aggragation variable collegamentotempiobbiettivo[0]."name of the variable i wanted to recall". example collegamentotempiobbiettivo[0].cld will return B119
I needed to accomplish something similar to the above (i.e. use aggregation pipeline -- in my case to do a "join" using $lookup -- and similarly returning a single (non-array) object only). However, I also needed to return a Promise for consistency. I added a then after the .exec as follows to extract the object:
return myModel
.aggregate([
{ $match: {
_id: ObjectId(args._id)}
},
{
$lookup: {
from: "items",
localField: "_id",
foreignField: "itemId",
as: "items"
}
}
])
.exec(function(err, pipelines) {
if (err) {
console.log('Error: ', err);
return Promise.reject(new InternalError());
}
})
.then(items => items[0]);
Officially, the aggregate command takes a "list" of pipeline arguments as it's main input. This is why the "Array" syntax is preferred. Though it is not strictly implemented this way by the mongoose method you appear to be using, this is likely to change.
The "Official" arguments are
An array representing the pipeline conditions
An options document specifying various options to alter the behavior.
So the mongoose form here is just looking for which item in the "list" is a function() and considers everything beforehand to be pipeline. But this will have to change in the future. Your question though seems to be more about "expecting" the different form to produce either a "document" or an "array" in response. But this will not happen.
You don't really and there is a good reason why. The aggregation framework either performs manipulation on collection content just as with $project or otherwise "groups" information such as with $group.
The only ways in which you generally expect only "one" result to return is when you either specifically $match to obtain only one result or otherwise $limit the response to one or even if your $group is on a singular or null value.
It is generally expected to be a "collection" of results or here represented as an array. Modern MongoDB servers and driver implementations can in fact return a "cursor", so the results can be larger than the 16MB BSON limit with newer versions. But still basically a list.
So it's always an array at present with something like "mongoose", which it looks like you are using. Just return the "first element" when it is all you want. Possibly even limit to 1 as well:
MyModel.aggregate(
[
{ "$match": ... },
{ "$group": ... },
{ "$limit": 1 }
], function(err, result) {
console.log(result[0]);
});
Which is essentially all that methods like .findOne() are doing under the covers anyway.