observe only specific property of object for every object in an observableArray

Question

I know about 'Drilling down into arrays/objects' from the documentation ( http://knockoutjs.com/documentation/plugins-mapping.html ), but I want this to work for every object in an array of objects, not only for one index like in the example

var data = {
    a: "a",
    b: [{ b1: "v1" }, { b2: "v2" }] 
};
var result = ko.mapping.fromJS(data, { observe: "b[0].b1"});

Is there a way to do this or do I have to run through the array and do it manually anyway? (then I wouldn't need the mapping plugin to begin with).

Answer 1

You cannot do this with the "drilling down" syntax but you can nest the mapping configurations using the create option:

var result = ko.mapping.fromJS(data, {
    observe: " ", // to copy every other property, a in this example 
    b: {
        create: function (options) {
            return ko.mapping.fromJS(options.data, {
                observe: "b1"
            });
        }
    }
});

Demo JSFiddle.

Using this only the b1 properties will be observable: