how to map and mergeObjects of an array of an array

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")
       }
  }
]
}

Takis · Accepted Answer · 2022-01-11 23:56:48Z

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"}}}}])

answered Jan 11, 2022 at 23:56

Takis

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1 Comment

enavuio Over a year ago

Thank you so much - I was going to ask why such aggravated "$$bs" pointer but realized short for birthdayservice lol. @Takis

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