Node js mongodb updating array with index in variable

Question

Node js mongodb updating array with index in variable

I have a mongoDB document, which, when in object form, you would access the desired array like this:

map.layers.1.data.INDEX

And this is what I currently have:

//Where = index, to = change to this
selector["data.layers.1.data."+where];
mDB.update({"_id":msg.island+msg.map}, {$set:{selector:to}} , function(err, doc) {
    console.log(doc);
});

(I made my map with Tiled.) Where data is an array, and I want to update just that one array index. But that index has to come from a variable. Is there a way to do this in mongoDB?

I'm currently reading whole document then replacing wanted data and then updating whole document. And that's not good, fast or necessary(I hope).

javascript
arrays
node.js
mongodb

Answer 1

Not sure I understood your description - an example document would be helpful - but I'll wing it. Assuming your documents look like

{
    "data" : {
        "layer" : [
            { "data" : [ 2, 5] },
            { "data" : [ 99 ] },
            { "data" : [ 0, 1, 2, 3 ] },
            { "data" : [ -1, "truffles", 6 ] },
        ]
    }
}

then you could update a fixed index of the array data.layer.2.data stored as the value of a variable myIndex like so in the mongo shell (similar to node but synchronous, no callback)

var myIndex = complicatedprocedureforgeneratingtheindex() // myIndex = 1
var mySet = {}
mySet["data.layer.2.data." + myIndex] = to
db.map.update(myQuery, { "$set" : mySet })
db.map.find(myQuery)
{
    "data" : {
        "layer" : [
            { "data" : [ 2, 5] },
            { "data" : [ 99 ] },
            { "data" : [ 0, 99, 2, 3 ] },
            { "data" : [ -1, "truffles", 6 ] },
        ]
    }
}

Roughly (i.e. ideas are there but no copy paste b/c of undefined variables)

Answer 2

This is exactly the answer!

In order to update an array with an given index, you have to define an object seperately, before the update:

set = {};

and then specify the index as a property of the object with [] embraces.

set['example.nested.object.' + i] = foo;

Then just update your MongoDB

Collection.update($set: set);

Should work.