add property to nested array in mongodb document

Question

I have a mongodb document with the following structure

> db.user.find().limit(1);
{ "_id" : "1", "foo" : { "bars" : [
    {
        "name" : "bar1"
    },
    {
        "name" : "bar2"
    },
], ... }, ... }

I want to add a new property to each bar. I've got my script iterating over the bars array, but I can't get the new property in there, how can I do this?

var users = db.user.find({"foo.bars":{$exists:true}});

users.forEach(function(user) {
    user.foo.bars.forEach(function(bar)
    {
       printjson(bar);
       //how can I specify the current 'bar' in this update?
       //db.experience.update({_id: user._id}, {$set: {"what goes here?" : "newbarValue"}});
    });
});

Answer 1

So says the preacher man:

var users = db.user.find({"foo.bars":{$exists:true}});

users.forEach(function(user) {
    var id = user._id;

    var foo_bars = user.foo.bars;
    var new_foo_bars = [];

    for(var i = 0; i < foo_bars.length; i++) {
        var foo_bar = foo_bars[i];
        foo_bar['newkey'] = 'newvalue';
        new_foo_bars.push(foo_bar);
    }

    db.user.update({"_id":id}, {$set:{"foo.bars":new_foo_bars}});
});

Answer 2

I have noticed that you are scrolling through the array on the client side there in JS.

If you were to form a new "bars" array from the old one then push it in as a whole new value this would mean you only do one DB call and the code is quite elegant.

If MongoDB does not support it normally it is better to just do the work on the client side.