How do I add a property to a breeze entity in the ViewModel, to assist with View display?

Question

How do I add a knockoutobserable property to a breeze entity - IsSelected(), in the ViewModel, to assist with View display?

IsSelected is not a field in the entity nor should it be, however I need to flag entites as selected for UI DOM manipulation (adding/removing css classes, etc.)

IsSelected is really a UI thing, but this is where the MVVM pattern gets cloudy for me.

Answer 1

You can extend your breeze entities by using the metadataStore.registerEntityTypeCtor method

In some of my projects I have a separate function to extend each entity.

So you will end up with something like this.

function extendProduct(metadataStore) {
    var ctor = function () {

    };
    var initialiser = function (entity) {
        entity.isSelected= ko.observable(false);

        return entity;
    };

    metadataStore.registerEntityTypeCtor('Product', ctor, initialiser);
}

I generally use the initialiser as it gets called after breeze has hydrated the entity by adding all its additional properties etc.

I generally stay away from the contstructor method as it gets called as the very first step in breeze hydrating the entity.