Formatting dates with $dateToString in nested arrays - arrays

Question

I have a collection of documents where each document represents a location of charging stations. I'm trying to use $map and $dateToString to transform each last_updated field into a string and drop the milliseconds portion of the datetime. There can be up to 3 last_updated fields on a location. A top level last_updated, a last_updated for each evse within an evses array, and a last_updated field within each connector of each evse. It is also possible for the evses array to not be present.
Here is an example of 2 locations:
[
{
"id" : "A",
"name" : "Meades Park",
"evses" : [
{
"uid" : "B",
"connectors" : [
{
"id" : "C",
"standard" : "IEC_62196_T1",
"last_updated" : ISODate("2021-02-18T23:54:56.000Z")
}
],
"last_updated" : ISODate("2021-02-18T23:54:56.000Z")
},
{
"uid" : "D",
"connectors" : [
{
"id" : "E",
"standard" : "IEC_62196_T1",
"last_updated" : ISODate("2021-02-18T23:54:56.000Z")
}
],
"last_updated" : ISODate("2021-02-18T23:54:56.000Z")
}
],
"last_updated" : ISODate("2021-12-14T23:42:06.000Z")
},
{
"id" : "F",
"name" : "5th Avenue",
"last_updated" : ISODate("2022-01-12T13:12:01.000Z")
}
]
I have my query working for the top level last_updated field and the evses.last_updated field, but I am having trouble modifying the evses.connectors.last_updated field. This is my query:
db.collection.aggregate([
{
$addFields: {
last_updated: { $dateToString: { format: '%Y-%m-%dT%H:%M:%SZ', date: '$last_updated' } },
evses: {
$map: {
input: '$evses',
as: 'evse',
in: {
{
$mergeObjects: [
'$$evse',
{ last_updated: { $dateToString: { format: '%Y-%m-%dT%H:%M:%SZ', date: '$$evse.last_updated' } } }
]
}
}
}
}
}
}
])
Is it possible to do another $map within the $map.in object? I was able to get this working by turning in into an array, but this changed the way the data was returned.
Here is an example of my query using $map.in as an array:
db.collection.aggregate([
{
$addFields: {
last_updated: { $dateToString: { format: '%Y-%m-%dT%H:%M:%SZ', date: '$last_updated' } },
evses: {
$map: {
input: '$evses',
as: 'evse',
in: [
{
$mergeObjects: [
'$$evse',
{ last_updated: { $dateToString: { format: '%Y-%m-%dT%H:%M:%SZ', date: '$$evse.last_updated' } } }
]
},
{
$map: {
input: '$$evse.connectors',
as: 'connector',
in: {
$mergeObjects: [
'$$connector',
{ last_updated: { $dateToString: { format: '%Y-%m-%dT%H:%M:%SZ', date: '$$connector.last_updated' } } }
]
}
}
}
]
}
}
}
])
In this case the returned documents look like this:
[
{
"id" : "A",
"name" : "CHARGEPOINT WVCC 1684DELL 1",
"evses" : [
[
{
"uid" : "B",
"connectors" : [
{
"id" : "C",
"standard" : "IEC_62196_T1",
"last_updated" : ISODate("2021-02-18T23:54:56.000+0000")
}
],
"last_updated" : "2021-02-18T23:54:56Z"
},
[
{
"id" : "C",
"standard" : "IEC_62196_T1",
"last_updated" : "2021-02-18T23:54:56Z"
}
]
],
[
{
"uid" : "D",
"connectors" : [
{
"id" : "E",
"standard" : "IEC_62196_T1",
"last_updated" : ISODate("2021-02-19T22:15:43.000+0000")
}
],
"last_updated" : "2021-02-19T22:15:43Z"
},
[
{
"id" : "E",
"standard" : "IEC_62196_T1",
"last_updated" : "2021-02-19T22:15:43Z"
}
]
]
],
"last_updated" : "2021-12-14T23:42:06Z"
},
{
"id" : "F",
"name" : "5th Avenue",
"last_updated" : "2022-01-12T13:12:01Z",
evses: null
}
]
Is it possible to perform a $map within another $map without duplicating the evses.connectors array and nesting them in another array?

Answer 1

Your query should be as below:
Remove the [] from in for the $map.
Merge objects for $$evse, last_updated document and connectors document.
db.collection.aggregate([
{
$addFields: {
last_updated: {
$dateToString: {
format: "%Y-%m-%dT%H:%M:%SZ",
date: "$last_updated"
}
},
evses: {
$map: {
input: "$evses",
as: "evse",
in: {
$mergeObjects: [
"$$evse",
{
last_updated: {
$dateToString: {
format: "%Y-%m-%dT%H:%M:%SZ",
date: "$$evse.last_updated"
}
}
},
{
connectors: {
$map: {
input: "$$evse.connectors",
as: "connector",
in: {
$mergeObjects: [
"$$connector",
{
last_updated: {
$dateToString: {
format: "%Y-%m-%dT%H:%M:%SZ",
date: "$$connector.last_updated"
}
}
}
]
}
}
}
}
]
}
}
}
}
}
])
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