Beginner mogndb user - why can't I see the _id of a doc in the compass shell and how to rename an object field in an embedded array

Working with Data Developer Tools
,
#1

I’m learning mongo shell, using the compass UI. I am trying to return the document _id so I can then rename a field within an array of that document.

Firstly, I was trying to get the doc _id but I can’t get it to print in the shell.

I tried targeting it as so

doc._id

all i see in the console is {}.

My other question, the real question is I’m trying to rename a field in an object, that is embedded in an array. my thought was I could get the specific doc ids, then update those docs using a foreach or something.

I’ve spent many hours trying many different tactics but I end up with one of two things happening:

  1. all documents are updated
  2. Only the correct documents are updated but not correctly, for example the ‘new service’ field is added to all service categories not just service_category_1.service_subcategory_2

here is my basic command from the shell:

db.collection.find({"services.tags.region1.service_category_1.service_subcategory_2": {$exists: 1}})
  .forEach( function( doc ) {
    if(doc.services){
      doc.services.forEach(function (service){
        //here, for each instance of  
       //services.tags.region1.service_category_1.service_subcategory_2
      //I want to rename all instances of 'service_subcategory_2' to 'new_service'

      })
    }
  }
  )

I also tried aggregation but I’m not wrapping my head around how it’s supposed to work. I looked here, How to rename a field name inside nested array?

Here is some sample data for one doc:

[{
  "_id": {
    "$oid": "5e7e4bd9d54f1760921a3b01"
  },
  "services": [
    {
      "_id": {
        "$oid": "5e7e4bd9d54f1760921a3b1b"
      },
      "tags": {
        "region_1": {
          "service_category_1": {
            "service_subcategory_2": "true"
          },
          "service_category_2": {
            "service_subcategory_3": "true"
          }
        }
      },
    },
    {
      "_id": {
        "$oid": "5e7e4bd9d54f1760921a3b1d"
      },
      "tags": {
        "region_1": {
          "service_category_1": {
            "service_subcategory_2": "true"
          }
        }
      },
    },
    {
      "_id": {
        "$oid": "5e7e4bd9d54f1760921a3b1f"
      },
      "tags": {
        "region_1": {
          "service_category_1": {
            "service_subcategory_4": "true",
            "service_subcategory_2": "true"
          }
        }
      },
    },
    {
      "_id": {
        "$oid": "5e7e4bd9d54f1760921a3b22"
      },
      "tags": {
        "region_1": {
          "service_category_1": {
            "service_subcategory_4": "true"
          },
          "service_category_2": {
            "service_subcategory_3": "true"
          }
        }
      },
    },
    {
      "_id": {
        "$oid": "5e7e4bd9d54f1760921a3b27"
      },
      "tags": {
        "region_1": {
          "service_category_1": {
            "service_subcategory_5": "true"
          }
        }
      },
    },
    {
      "_id": {
        "$oid": "5e7e4bd9d54f1760921a3b2c"
      },
      "tags": {
        "region_1": {
          "service_category_1": {
            "service_subcategory_5": "true"
          }
        }
      },
    },
    {
      "_id": {
        "$oid": "5e7e4bd9d54f1760921a3b2e"
      },
      "tags": {
        "region_1": {
          "service_category_1": {
            "service_subcategory_5": "true"
          }
        }
      },
    },
    {
      "_id": {
        "$oid": "5e7e4bd9d54f1760921a3b30"
      },
      "tags": {
        "region_1": {
          "service_category_1": {
            "service_subcategory_2": "true"
          }
        }
      },
    },
    {
      "_id": {
        "$oid": "5e7e4bd9d54f1760921a3b32"
      },
      "tags": {
        "region_1": {
          "service_category_1": {
            "service_subcategory_2": "true"
          }
        }
      },
    },
    {
      "_id": {
        "$oid": "61ea350aad77ef002ef20fd8"
      },
      "tags": {
        "region_1": {
          "service_category_3": "true"
        }
      },
    }
  ]
}]