Mongodb: Insert key:value into object

In my playing with Mongodb over the past few weeks I am developing more and more complex applications, in my latest project i would like to insert a key:value into an object. I am using mongojs & node.js.

I am generating a dynamic key (ie: hash = 3gx83h7) for my new key:value to be pushed into the object paths. I know I can do the following:

db.applications.update({'apikey':key,'uid':user._id}, {'$set':{'paths.hash':0}},function(err){
    if(!err){}
});

But that will push a key:value similar to this:

paths:{
    hash:0
}

How can i push in my generated hash as the key?

You need to assemble the key name programmatically so that hash's value is used:

var setValue = {};
setValue['paths.' + hash] = 0;

db.applications.update(
    {'apikey': key, 'uid': user._id}, 
    {'$set': setValue}, 
    function(err){
        if(!err){}
    }
);