ko.mapping create function, extend object

Question

Is it possible to modify the (for lack of a better term) schema of an object during the mapping process? I would imagine it is, I just can't seem to get it to work. I'm trying something like this:

var data = {
    itemOne: 'someData',
    itemTwo: 'moreData'
}

var mapping = {
    "newItem": {
          create: function(options) {
            return ko.observable(false);
          }
    }
};

ko.mapping.fromJS(data, mapping, _model.observableArrayPart);

Answer 1

Here is a sample that shows customizing how your array is creating and defining a key for it, so that you can apply updates using the mapping plugin: http://jsfiddle.net/rniemeyer/LHeQZ/

var data = [
    { id: 1, first: "Bob", last: "Smith" },
    { id: 2, first: "Jim", last: "Jones" },
    { id: 3, first: "Delete", last: "Me" }
];

var updatedData = [
    { id: 1, first: "Robert", last: "Smith" },
    { id: 2, first: "James", last: "Jones" },
    { id: 4, first: "New", last: "Guy" }
];

var Person = function(data) {
    this.id = data.id;
    this.first = ko.observable(data.first);
    this.last = ko.observable(data.last);
    this.full = ko.computed(function() {
        return this.first() + " " + this.last();
    }, this);        
};


var dataMappingOptions = {
    key: function(data) {
        return data.id;        
    },
    create: function(options) {
        return new Person(options.data);
    }        
};


var viewModel = {
    people: ko.mapping.fromJS([]),
    loadInitialData: function() {
        ko.mapping.fromJS(data, dataMappingOptions, viewModel.people);        
    },
    loadUpdatedData: function() {
        ko.mapping.fromJS(updatedData, dataMappingOptions, viewModel.people);  
    }        
};

ko.applyBindings(viewModel);