Idea for a utility method that maps ASP.NET MVC ModelState to "_ValidationErrors" observable array properties on a Knockout view model.

gistfile1.txt

(function (lab, $, undefined) {

    lab.Utils = new (function () {
        return {
            UpdateValidationErrors: function (viewModel, modelState) {
                var keySeparator = new RegExp("[.\\[\\]]+");
                for (var key in modelState) {
                    if (!modelState[key]) {
                        continue;
                    }
                    var errors = modelState[key].Errors;
                    var propertyChain = key.split(keySeparator);
                    var currentObject = viewModel;
                    var currentPropertyName = propertyChain.shift();
                    var targetObject = null;
                    while (currentObject && currentObject[currentPropertyName]) {

                        if (propertyChain.length === 0) {
                            targetObject = currentObject[currentPropertyName];
                            break;
                        }

                        currentObject = ko.utils.unwrapObservable(currentObject[currentPropertyName]);
                        currentPropertyName = propertyChain.shift();
                    }

                    if (targetObject) {
                        targetObject._ValidationErrors($.map(errors, function (item) {
                            return item.ErrorMessage;
                        }));
                        delete modelState[key];
                    }
                }

                // All remaining modelstate errors are "global"
                var globalErrors = [];
                for (key in modelState) {
                    globalErrors = globalErrors.concat($.map(modelState[key].Errors, function (item) {
                        return item.ErrorMessage;
                    }));
                }
                viewModel._ValidationErrors(globalErrors);
            }
        };
    })();

} (window.lab = window.lab || {}, jQuery));