Aggregate nested arrays - mongodb

Question

I have multiple documents, and I'm trying to aggregate all documents with companyId = xxx and return one array with all the statuses.
So it will look like this:
[
{
"status": "created",
"date": "2019-03-16T10:59:59.200Z"
},
{
"status": "completed",
"date": "2019-03-16T11:00:37.750Z"
},
{
"status": "created",
"date": "2019-03-16T10:59:59.200Z"
},
{
"status": "completed",
"date": "2019-03-16T11:00:37.750Z"
},
{
"status": "created",
"date": "2019-03-16T10:59:59.200Z"
},
{
"status": "completed",
"date": "2019-03-16T11:00:37.750Z"
},
{
"status": "created",
"date": "2019-03-16T10:59:59.200Z"
},
{
"status": "completed",
"date": "2019-03-16T11:00:37.750Z"
}
]
The document look like this:
[
{
"companyId": "xxx",
"position": "",
"section": "",
"comment": "",
"items": [
{
"any": "111",
"name": "some name",
"description": "some description",
"version": "3",
"status": [
{
"status": "created",
"date": "2019-03-16T10:59:59.200Z"
},
{
"status": "completed",
"date": "2019-03-16T11:00:37.750Z"
}
]
},
{
"any": "222",
"name": "some name",
"description": "some description",
"version": "3",
"status": [
{
"status": "created",
"date": "2019-03-16T10:59:59.200Z"
},
{
"status": "completed",
"date": "2019-03-16T11:00:37.750Z"
}
]
}
]
},
{
"companyId": "xxx",
"position": "",
"section": "",
"comment": "",
"items": [
{
"any": "111",
"name": "some name",
"description": "some description",
"version": "3",
"status": [
{
"status": "created",
"date": "2019-03-16T10:59:59.200Z"
},
{
"status": "completed",
"date": "2019-03-16T11:00:37.750Z"
}
]
},
{
"any": "222",
"name": "some name",
"description": "some description",
"version": "3",
"status": [
{
"status": "created",
"date": "2019-03-16T10:59:59.200Z"
},
{
"status": "completed",
"date": "2019-03-16T11:00:37.750Z"
}
]
}
]
}
]
Any suggestion, how to implement this?
Then I want to loop over the array (in code) and count how many items in status created, and completed. maybe it could be done with the query?
Thanks in advance

Answer 1

You can use below aggregation:
db.col.aggregate([
{
$match: { companyId: "xxx" }
},
{
$unwind: "$items"
},
{
$unwind: "$items.status"
},
{
$replaceRoot: {
newRoot: "$items.status"
}
},
{
$group: {
_id: "$status",
count: { $sum: 1 }
}
}
])
Double $unwind will return single status per document and then you can use $replaceRoot to promote each status to root level of your document.
Additionally you can add $group stage to count documents by status.

Answer 2

In addition to the #mickl answer, you can add $project pipeline to get the result as a flat list of status and count.
db.collectionName.aggregate([
{
$match: { companyId: "xxx" }
},
{
$unwind: "$items"
},
{
$unwind: "$items.status"
},
{
$replaceRoot: {
newRoot: "$items.status"
}
},
{
$group: {
_id: "$status",
count: { $sum: 1 }
}
},
{
$project: {
"status":"$_id",
"count":1,
_id:0
}
}
])

Answer 3

If the number of documents on which you are executing the above query is too much then you should avoid using $unwind in the initial stage of aggregation pipeline.
Either you should use $project after $match to reduce the selection of fields or you can use below query:
db.col.aggregate([
{
$match: {
companyId: "xxx"
}
},
{
$project: {
_id: 0,
data: {
$reduce: {
input: "$items.status",
initialValue: [
],
in: {
$concatArrays: [
"$$this",
"$$value"
]
}
}
}
}
},
{
$unwind: "$data"
},
{
$replaceRoot: {
newRoot: "$data"
}
}
])