MongoDB aggregation: group and push multiple attributes - mongodb

Question

I am having a problem with my query using MongoDB aggregation.
I have a collection as follows:
[
{
id: 1,
name: 'cash',
amount: 10,
},
{
id: 2,
name: 'IPT',
amount: 10,
terminal_type: 'inside',
card: {
id: 1,
name: 'visa',
},
},
{
id: 2,
name: 'IPT',
amount: 10,
terminal_type: 'outside',
card: {
id: 1,
name: 'visa',
},
},
]
Expected result:
[
{
id: 1,
name: 'cash',
amount: 10,
},
{
id: 2,
name: 'IPT',
amount: 20,
cards: [
{
id: 1,
name: 'visa',
amount: 20,
},
],
terminals: [
{
name: 'inside',
amount: 10,
},
{
name: 'outside',
amount: 10,
},
],
},
]
What I have tried:
{
$group: {
_id: {
id: '$id',
card_id: '$card.id',
terminal_type: '$terminal_type',
},
name: {$first: '$name'},
amount: {$sum: '$amount'},
card_name: {$sum: '$card.name'},
}
},
{
$group: {
_id: {
id: '$id',
card_id: '$_id.card_id',
},
name: {$first: '$name'},
amount: {$sum: '$amount'},
card_name: {$first: '$card_name'},
terminals: {
$push: {
{ $cond: [
{$ifnull: ['$terminal_type', false]},
{
type: '$terminal_type',
amount: '$amount',
},
'$$REMOVE',
]
}
}
}
}
},
{
$group: {
_id: '$_id.id',
name: {$first: '$name'},
amount: {$sum: '$amount'},
cards: {
$push: {
{ $cond: [
{$ifnull: ['$id.card_id', false]},
{
id: '$_id.card_id',
name: '$card_name',
amount: '$amount',
},
'$$REMOVE',
],
},
},
terminals: // This is the problem where I can't figure out how get this value
}
}
I considered to unwind terminals before the last group pipeline but I ended up getting duplicate documents which make the sum for the amount incorrect. Can anyone help me to solve this or point me to where I can read and understand more about this? Thank you very much.

Answer 1

One option to go is to $group and then $reduce:
db.collection.aggregate([
{$group: {
_id: "$id",
name: {$first: "$name"},
amount: {$sum: "$amount"},
terminals: {$push: {name: "$terminal_type", amount: "$amount"}},
cards: {$push: {id: "$card.id", name: "$card.name", amount: "$amount"}},
cardIds: {$addToSet: "$card.id"},
terminalNames: {$addToSet: "$terminal_type"}
}},
{ $project: {
_id: 0, id: "$_id", name: 1, amount: 1,
cards: {
$map: {
input: "$cardIds",
as: "card",
in: {
id: "$$card",
amount: {$reduce: {
input: "$cards",
initialValue: 0,
in: {$add: [
"$$value",
{$cond: [{$eq: ["$$card", "$$this.id"]},"$$this.amount", 0]}
]}
}},
name: {$reduce: {
input: "$cards",
initialValue: "",
in: {$cond: [{$eq: ["$$this.id", "$$card"]}, "$$this.name", "$$value"]}
}}
}
}},
terminals: {
$map: {
input: "$terminalNames",
as: "terminal",
in: {
name: "$$terminal",
amount: {$reduce: {
input: "$terminals",
initialValue: 0,
in: {$add: [
"$$value",
{$cond: [{$eq: ["$$terminal", "$$this.name"]}, "$$this.amount", 0]}
]}
}}
}
}
}
}}
])
See how it works on the playground example
Another option may be to use $unwind as you mentioned:
db.collection.aggregate([
{$group: {
_id: "$id",
name: {$first: "$name"},
amount: {$sum: "$amount"},
terminals: {$push: {
type: "terminal",
name: "$terminal_type",
key: "$terminal_type",
amount: "$amount"
}},
cards: {$push: {
type: "card",
id: "$card.id",
key: "$card.id",
name: "$card.name",
amount: "$amount"
}}
}},
{$project: {amount: 1, name: 1, docs: {$concatArrays: ["$cards", "$terminals"]}}},
{$unwind: "$docs"},
{$group: {
_id: {_id: "$_id", type: "$docs.type", key: "$docs.key"},
amount: {$sum: "$docs.amount"},
name: {$first: "$docs.name"},
dataAmount: {$first: "$amount"},
dataName: {$first: "$name"}
}},
{$group: {
_id: "$_id._id",
amount: {$first: "$dataAmount"},
name: {$first: "$dataName"},
terminals: {$push: {
$cond: [
{$and: [{$eq: ["$_id.type", "terminal"]}, {$gt: ["$name", null]}]},
{amount: "$amount", name: "$name"},
"$$REMOVE"
]
}},
cards: {$push: {
$cond: [
{$and: [{$eq: ["$_id.type", "card"]}, {$gt: ["$name", null]}]},
{amount: "$amount", name: "$name", id: "$_id.key"},
"$$REMOVE"
]
}}
}}
])
See how it works on the playground example