Update Sub-Document properties using a Variable In Key Name

Question

I know how to update objects within an array like the following:

db.bar.update( {user_id : 123456 , "items.item_name" : "my_item_two" } , 
                {$inc : {"items.$.price" : 1} } , 
                false , 
                true);

But, im trying to currently update a object.

model:

  boats: {
        cash: {type: Number, default: 0},
        amount: { type: Number, default: 0}
    },
    murder: {
        attempts: {type: Number, default:0},
        failed_attempts: {type: Number, default:0},
        successfull_attempts: {type: Number, default:0},
        cash: {type: Number, default: 0},
        amount: { type: Number, default: 0}
    },
    orgcrime: {
        cash: {type: Number, default: 0},
        amount: { type: Number, default: 0}
    },

i have a variable called type that contains the word i want to update, for example: murder . I also have a variable called num, that will be updated value.

CurrentStats contains the full model result.

i get the types object by doing:currentStats[type]` , but how can i update it?

i tried with:

var x = {};
        x[type].cash = num;
        x[type].amount = 1;

and {$inc: x} , but that wouldnt work.

How would i go about this?

Neil Lunn · Accepted Answer · 2017-09-21 12:31:30Z

1

You mean to actually form the field names using "Dot Notation", by concatenating the name of the key:

var type = "murder";

var x = { };

x[type + ".cash"] = 1;
x[type + ".amount"] = 2;

db.bar.update({},{ "$inc": x });

Modern ES6 Notation also allows other forms like :

db.bar.update(
  {},
  { 
    "$inc": {
      [type + ".cash"]: 1,
      [`${type}.amount`]: 2
    }
  }
);

Either way forms

{
  "$inc": {
    "murder.cash": 1,
    "murder.amount": 2
  }
}

Which is what you want to update those properties and only those properties when making changes to the document.

answered Sep 21, 2017 at 12:31

Neil Lunn

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