Update a nested array of a record in mongodb collection

Let's say you want to dynamically update an element of an array which belong to a certain collection. So basically you have some model which looks like :

Collection.name = {
   somestring:'some name',
   anArray:[]
}

Reading the docs here :

http://docs.mongodb.org/manual/reference/method/db.collection.update/#update-an-element-by-position and there : http://docs.mongodb.org/manual/reference/operator/update/positional/ or here :

You can get pretty neat information. Unfortunately when using some libs like mongoose or frameworks like meteorjs you can struggle with the fact that you have a dynamic field for the array index and the dot notation fails. So instead of this simple line of code :

db.bios.update(
   { _id: 1 },
   { $set: { "contribs.1": "ALGOL 58" } }
)

You end up with nothing :)

Who comes to the rescue, the object creation !

The idea is to simply create the object setter to update the collection. So instead of writting in plain { "contribs.1": "ALGOL 58" } you will prefer to write down :

var setter = {};
setter['contribs.1'] = 'ALGOL 58';
db.bios.update(
   { _id: 1 },
   { $set: setter}
)

Thus you can rewirte it withe the value from some param :

var setter = {};
setter['contribs'+req.index] = 'ALGOL 58';
db.bios.update(
   { _id: 1 },
   { $set: setter}
)

And voilà it works ! Enjoy !