How to use a variable as a field name in mongodb-native findAndModify?

In this code that uses the mongodb-native driver I’d like to increase the value of the field which I specify in a separate variable. The problem is that the field name in the $inc clause will be ‘variable’ in this case, not the contents of the variable. In the query part the variable selected works as expected and finds the correct id.

var selected = 'id_of_the_selected_one';
var variable = 'some_string';
collection.findAndModify(
     {_id : selected}, 
     {},
     {$inc : {variable : 1}},
     {new : true, upsert : true},
     function(err, autoincrement) { /* ... */ }
);

How should I do it so that instead of the word ‘variable’ there will be the contents of the variable?

Here is Solutions:

We have many solutions to this problem, But we recommend you to use the first solution because it is tested & true solution that will 100% work for you.

Solution 1

Set the key of another variable to its value and pass that as an object. Note of action:

var selected = 'id_of_the_selected_one';
var variable = 'some_string';
var action = {};
action[variable] = 1; // the value

collection.findAndModify(
    {_id : selected}, 
    {}, 
    {$inc : action}, 
    {new : true, upsert : true}, 
    function(err, autoincrement) { /* ... */ }
); // Same as {$inc: {'some_string': 1} }

Note: Use and implement solution 1 because this method fully tested our system.
Thank you 🙂

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