how to combine array of object result in mongodb - node.js

Question

how can i combine match document's subdocument together as one and return it as an array of object ? i have tried $group but don't seem to work.
my query ( this return array of object in this case there are two )
User.find({
'business_details.business_location': {
$near: coords,
$maxDistance: maxDistance
},
'deal_details.deals_expired_date': {
$gte: new Date()
}
}, {
'deal_details': 1
}).limit(limit).exec(function(err, locations) {
if (err) {
return res.status(500).json(err)
}
console.log(locations)
the console.log(locations) result
// give me the result below
[{
_id: 55 c0b8c62fd875a93c8ff7ea, // first document
deal_details: [{
deals_location: '101.6833,3.1333',
deals_price: 12.12 // 1st deal
}, {
deals_location: '101.6833,3.1333',
deals_price: 34.3 // 2nd deal
}],
business_details: {}
}, {
_id: 55 a79898e0268bc40e62cd3a, // second document
deal_details: [{
deals_location: '101.6833,3.1333',
deals_price: 12.12 // 3rd deal
}, {
deals_location: '101.6833,3.1333',
deals_price: 34.78 // 4th deal
}, {
deals_location: '101.6833,3.1333',
deals_price: 34.32 // 5th deal
}],
business_details: {}
}]
what i wanted to do is to combine these both deal_details field together and return it as an array of object. It will contain 5 deals in one array of object instead of two separated array of objects.
i have try to do it in my backend (nodejs) by using concat or push, however when there's more than 2 match document i'm having problem to concat them together, is there any way to combine all match documents and return it as one ? like what i mentioned above ?

Answer 1

What you are probably missing here is the $unwind pipeline stage, which is what you typically use to "de-normalize" array content, particularly when your grouping operation intends to work across documents in your query result:
User.aggregate(
[
// Your basic query conditions
{ "$match": {
"business_details.business_location": {
"$near": coords,
"$maxDistance": maxDistance
},
"deal_details.deals_expired_date": {
"$gte": new Date()
}},
// Limit query results here
{ "$limit": limit },
// Unwind the array
{ "$unwind": "$deal_details" },
// Group on the common location
{ "$group": {
"_id": "$deal_details.deals_location",
"prices": {
"$push": "$deal_details.deals_price"
}
}}
],
function(err,results) {
if (err) throw err;
console.log(JSON.stringify(results,undefined,2));
}
);
Which gives output like:
{
"_id": "101.6833,3.1333",
"prices": [
12.12,
34.3,
12.12,
34.78,
34.32
]
}
Depending on how many documents actually match the grouping.
Alternately, you might want to look at the $geoNear pipeline stage, which gives a bit more control, especially when dealing with content in arrays.
Also beware that with "location" data in an array, only the "nearest" result is being considered here and not "all" of the array content. So other items in the array may not be actually "near" the queried point. That is more of a design consideration though as any query operation you do will need to consider this.

Answer 2

You can merge them with reduce:
locations = locations.reduce(function(prev, location){
previous = prev.concat(location.deal_details)
return previous
},[])