MongoDB aggregate pipeline group - mongodb

Question

I am trying to build a pipeline which will search for documents based on certain criteria and will group certain fields to give desired output. Document structure of deals is
{
"_id":"123",
"status":"New",
"deal_amount":"5200",
"deal_date":"2018-03-05",
"data_source":"API",
"deal_type":"New Business",
"account_id":"A1"
},
{
"_id":"456",
"status":"New",
"deal_amount":"770",
"deal_date":"2018-02-11",
"data_source":"API",
"deal_type":"New Business",
"account_id":"A2"
},
{
"_id":"885",
"status":"Old",
"deal_amount":"4070",
"deal_date":"2017-09-22",
"data_source":"API",
"deal_type":"New Business",
"account_id":"A2"
},
Account name is referenced field. Account document goes like this:
{
"_id":"A1",
"name":"Sarah",
},
{
"_id":"A2",
"name":"Amber",
},
The pipeline should search for documents whose 'status' is 'New' and 'deal amount' is more than 2000 and it should group by 'account name'. Pipeline i have used goes like this
db.deal.aggregate([{
$match: {
status: New,
deal_amount: {
$gte: 2000,
}
}
}, {
$group: {
_id: "$account_name",
}
},{
$lookup:{
from:"accounts",
localField:"account_id",
foreignField:"_id",
as:"acc",
}
}
])
I want to show fields deal_amount, deal_type, deal_date and account name only in result.
Expected Result:
{
"_id": "123",
"deal_amount": "5200",
"deal_date": "2018-03-05",
"deal_type": "New Business",
"account_name": "Sarah"
}, {
"_id": "885",
"deal_amount": "4070",
"deal_date": "2017-09-22",
"deal_type": "New Business",
"account_name": "Amber"
},
Do i have to include all the these fields,deal_amount, deal_type, deal_date & account name, in 'group' stage in order to show in result or is there any other ways to do it. Any help is highly appreciated.

Answer 1

Please use this query.
aggregate([{
$match: {
status: "New",
deal_amount: {
$gte: 2000,
}
}
},
{
$lookup:{
from:"accounts",
localField:"account_id",
foreignField:"_id",
as:"acc",
}
},
{
$unwind: {
path: '$acc',
preserveNullAndEmptyArrays: true,
},
},
{
$group: {
_id: "$acc._id",
deal_amount: { $first: '$deal_amount' },
deal_date: { $first: '$deal_date' },
deal_type: { $first: '$deal_type' },
}
}
])
You can do by :
1) using $$ROOT
reference: link
{ $group : {
_id : "$author",
data: { $push : "$$ROOT" }
}}
2) by assign single parameter
{
$group: {
_id: "$account_name",
deal_amount: { $first: '$deal_amount' },
deal_date: { $first: '$deal_date' },
.
.
}
}

Answer 2

Not sure why you need $group stage. You just need to add $project stage to output the account name from the referenced collection.
{
"$project": {
"deal_amount": 1,
"deal_type": 1,
"deal_date": 1,
"account_name": {"$let":{"vars":{"accl":{"$arrayElemAt":["$acc", 0]}}, in:"$$accl.name}}
}
}

Answer 3

One thing to start with, your $gte operator doesn't work on the string field deal_amount, so you might want to change the field to integers or something similar:
// Convert String to Integer
db.deals.find().forEach(function(data) {
db.deals.update(
{_id:data._id},
{$set:{deal_amount:parseInt(data.deal_amount)}});
Then, to get just the fields you need, reshape the document using $project:
db.deals.aggregate([{
$match: {
"status": "New",
"deal_amount" : {
"$gte" : 2000
}
}
},
{
$lookup:{
from:"accounts",
localField:"account_id",
foreignField:"_id",
as:"acc",
}
},
{
$project: {
_id: 1,
deal_amount: 1,
deal_type: 1,
deal_date: 1,
"account_name": {"$let":{"vars":{"accl":{"$arrayElemAt":["$acc", 0]}}, in:"$$accl.name"}}
}
}
]);
For me, this produced:
{
"_id" : "123",
"deal_amount" : 5200.0,
"deal_date" : "2018-03-05",
"deal_type" : "New Business",
"account_name" : "Sarah"
}

Answer 4

db.deal.aggregate([{$match: {status: {$eq: 'New'}, deal_amount: {$gte: '2000'}}}, {$group: {_id: {accountName: '$account_id', type: '$deal_type', 'amount': '$deal_amount'}}}])