how to map and mergeObjects of an array of an array - mongodb

Question

I want to apply a mergeObjects and map of an Array of an Array:
I am able to complete the mapping and merging when I am one level of Array in but if the Array has another array, I am unsure how to apply another map/merge object.
{
_id: "123",
date: "1900-01-01T11:00:00.0000000",
name: "joe",
birthdayservice: [
{
"date": "1999-01-01",
"team" : [
{
"requestedDate": "1999-01-01"
},
{
"requestedDate": "1999-05-01"
}
},
{
"date": "1998-01-01",
"team" : [
{
"requestedDate": "1999-01-01"
},
{
"requestedDate": "1999-05-01"
}
}
]
}
I am able to map through the first array in birthdayservice to converte date to an ISO_Date/todate such as:
{
"$addFields": {
"birthdayservice": {
$map: {
input: "$birthdayservice", //this is an array
in: {
"$mergeObjects": [
"$$this",
{
"date": {
"$toDate": "$$this.date"
}
}
]}
}
}
}
}
but when I get into more of a nested value, I get
$mergeObjects requires object inputs, but input is an array
{
"$addFields": {
"birthdayservice": {
$map: {
input: "$birthdayservice", //this is an array
in: {
"$mergeObjects": [
"$$this",
{
"date": {
"$toDate": "$$this.date"
}
}
]}
}
}
}
},
{
"$addFields": {
"birthdayservice": {
$map: {
input: "$birthdayservice.team", //also an array
in: {
"$mergeObjects": [
"$$this",
{
"requestedDate": {
"$toDate": "$$this.requestedDate"
}
}
]}
}
}
}
}
My end goal is to relace the date string fields to a date convert
birthdayservice.date
birthdayservice.team.requestedDate
Both to ISO_Dates as below:
{
_id: "123",
date: "1900-01-01T11:00:00.0000000",
name: "joe",
birthdayservice: [
{
"date": ISO_Date("1999-01-01T11:00:00.0000000Z"),
"team" : [
{
"requestedDate": ISO_Date("1999-01-01T11:00:00.0000000Z")
},
{
"requestedDate": ISO_Date("1999-05-01T11:00:00.0000000Z")
}
},
{
"date": "1998-01-01",
"team" : [
{
"requestedDate": ISO_Date("1999-01-01T11:00:00.0000000Z")
},
{
"requestedDate": ISO_Date("1999-05-01T11:00:00.0000000Z")
}
}
]
}

Answer 1

Query
this converts the all date strings to dates inside birthdayservice and teams array
map birthdayservice
convert the "date"
nested map to convert the dates in the team
the way the field is changed value is by mergeObjects
(in mongodb5 we have also setField to do this)
Test code here
aggregate(
[{"$set":
{"birthdayservice":
{"$map":
{"input":"$birthdayservice",
"in":
{"$mergeObjects":
["$$bs",
{"date":{"$toDate":"$$bs.date"},
"team":
{"$map":
{"input":"$$bs.team",
"in":
{"$mergeObjects":
["$$t", {"requestedDate":
{"$toDate":"$$t.requestedDate"}}]},
"as":"t"}}}]},
"as":"bs"}}}}])