Add New key at the end of each object inside an array

Question

I have data from mongodb like this from one collection.

/* 1 */
{
    "_id" : ObjectId("5be94355f220b62c7449dc0f"),
    "districts" : [ 
        {
            "name" : "NORTH AND MIDDLE",
            "code" : 632.0
        }, 
        {
            "name" : "EAST",
            "code" : 603.0
        }, 
        {
            "name" : "SOUTH",
            "code" : 602.0
        }
    ],
    "state" : "ISLANDS"
}

/* 2 */
{
    "_id" : ObjectId("5be94355f220b62c7441dc04"),
    "districts" : [ 
        {
            "name" : "Apple",
            "code" : 512.0
        }, 
        {
            "name" : "Ball",
            "code" : 522.0
        }
    ],
    "state" : "GOLD"
}

/* 3 */
{
    "_id" : ObjectId("5eee07816a011d391a45178"),
    "districts" : [ 
        {
            "name" : "DAM",
            "code" : 478.0
        }, 
        {
            "name" : "DEN",
            "code" : 481.0
        }, 
        {
            "name" : "DOG AND CAT",
            "code" : 461.0
        }
    ],
    "state" : "THE NAGAR AND HAVELI"
}

I was given an excel sheet like below as shown with no other information only 2 columns

My work is to add "Short Name of District" for all districts.

I tried below method

var tc = [
    "NORTH AND MIDDLE",
    "EAST",
    "SOUTH",
    "Apple",
    "Ball ",
    "DAM ",
    "DEN ",
    "DOG AND CAT"
]
 

db.dummy.find({"districts.name":{$in:tc}}).forEach(x => {
    x["districts"].forEach( y => {
        if (   
        y.name == "NORTH AND MIDDLE" ){
            y.short_name  = "NAM"
        }
        if (   
            y.name == "EAST" ){
                y.short_name  = "ET"
            }

        if (   
            y.name == "SOUTH" ){
                y.short_name  = "ST"
            }
    })
})

I got the result

/* 1 */
{
    "_id" : ObjectId("5be94355f220b62c7449dc0f"),
    "districts" : [ 
        {
            "name" : "NORTH AND MIDDLE",
            "code" : 632.0,
            "short_name" : "NAM"
        }, 
        {
            "name" : "EAST",
            "code" : 603.0,
        "short_name" : "ET"
        }, 
        {
            "name" : "SOUTH",
            "code" : 602.0,
        "short_name" : "ST"
        }
    ],
    "state" : "ISLANDS"
}

/* 2 */
{
    "_id" : ObjectId("5be94355f220b62c7441dc04"),
    "districts" : [ 
        {
            "name" : "Apple",
            "code" : 512.0,
        "short_name" : "Al"
        }, 
        {
            "name" : "Ball",
            "code" : 522.0
        "short_name" : "BA"
        }
    ],
    "state" : "GOLD"
}

/* 3 */
{
    "_id" : ObjectId("5eee07816a011d391a45178"),
    "districts" : [ 
        {
            "name" : "DAM",
            "code" : 478.0,
        "short_name" : "DA"
        }, 
        {
            "name" : "DEN",
            "code" : 481.0,
        "short_name" : "DN"
        }, 
        {
            "name" : "DOG AND CAT",
            "code" : 461.0
        "short_name" : "DAC"
        }
    ],
    "state" : "THE NAGAR AND HAVELI"
}

Is this is the only method ?? like using if loop for all districts or any other methods are there like using mongodb aggregate or any other javascript methods. It will be helpful if other methods are there as it will be problem to use if loop when there is 730 districts are there. I dont have experience in working with aggregate frameworks so i thought anyone might know other method.

Aggregation framework is used to process and return computed results from a collection. I think you're looking for bulkwrite method in mongodb apis. docs.mongodb.com/manual/reference/method/… . Also instead of mapping long names to short names using if, you can try to convert csv excel file to a json object. — v1shva
– v1shva, Commented Jun 21, 2020 at 5:23

grodzi · Accepted Answer · 2020-06-21 09:20:32Z

1

You may write a mapping:

const districtNameToShort = {
  'NORTH AND MIDDLE': 'NAM',
  'EAST': 'ET',
  ...
}

Then in your forEach

const districtNameToShort = {
  'NORTH AND MIDDLE': 'NAM',
  'EAST': 'ET'
}
db.dummy.find().forEach(x => {
  db.dummy.update(
    {_id : x._id},
    {$set: {
      districts: x.districts.map(district => {
        district.short_name = districtNameToShort[district.name] || district.name
        return district
      })
    }}
  )
})

edited Jun 21, 2020 at 9:20

answered Jun 21, 2020 at 6:18

grodzi

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5 Comments

Abhishek K V Over a year ago

Failed to execute script. Error: TypeError: redeclaration of const districtNameToShort is coming

grodzi Over a year ago

@AbhishekKV It simply means you copy pasted twice districtName... inside the shell. More importantly what needs to be understood is the usage of mapping to avoid hardcoding the if's. Also: I may if you ask review the update (since I mapped from x.name instead of x.districts.name) but I don't think it is necessary if you understood the idea ?

Abhishek K V Over a year ago

your script will create new key called short_name below state key i.e. outside districts array but i want inside districts array below each district

grodzi Over a year ago

@AbhishekKV no much change, I edited to replace at district level instead

Abhishek K V Over a year ago

Thank you very much now i got to know how mapping works and why error comes in mapping time :)

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