Extending entities on a per view basis with breeze.js in SPA - breeze

Question

Trying to figure out how to extend entities that I query from breeze.js on a per-view basis in a single page application. Right now breeze is acting as the gate-keeper when it comes to extending (a.k.a materializing) them and I’m wondering what other options are available to allow me to do this. I initially started with knockout’s mapping plugin but found that it refused to handle child collections for some reason so I moved to using breeze’s constructor function and initializer methodology. The problem with this is that you can only define one custom "model" for an entity. I am looking for approaches that would allow a custom "model" of an entity on a per-view basis. I’ve already ruled out multiple managers. Querying meta-data multiple times is a huge unnecessary hit just to get this working.
This diagram visualizes what I’m trying to achieve. Both View 1 and View 2 ultimately query Entity B and both views require their own specific customization of the "model" of Entity B. Since View 1 loads first it’s custom "model" of Entity B "wins" and View 2 doesn’t have the opportunity to customize it. When View 2 eventually runs it’s query, any entities of type B that were already loaded by View 1 will have the custom "model" that View 1 defined which will make View 2 explode during binding. Any entities not already loaded by View 1 will now have View 2's custom "model" which would eventually crash View 1 if it could even get that far down the road. See this post.
My thought was to manually create my own custom "model" for each view that has an Entity observable and I could then iterate over every entity returned from a breeze query and new up this custom "model" and pass in the current item, assigning it to the Entity property. I don't really want to do this because I now have I'll have tons of iteration code everywhere and I'd much rather use knockout's mapping plugin. Pseudo code:
function view1EntityBModel(entity) {
var self = this;
self.Entity = ko.observable(entity);
self.myCustomProperty = ko.observable();
...
}
function view2EntityBModel(entity) {
var self = this;
self.Entity = ko.observable(entity);
self.isExpanded = ko.observable(false);
...
}
I was wondering if there are any other solutions available to achieve this same goal?
Or even better does anyone know how to make the knockout mapping plugin working on child collections?
I think the problem here is that by the time the mapping plugin gets a-hold of the breeze data the Children collection has already been converted into an observable array and the mapping plugin doesn't know that it needs to "call" the Children() property in order to get back a list.
var categoryMapper = {
create: function (options) {
return new categoryModel(options.data);
},
Children: { // this doesn't fire for the children
create: function (options) {
return new categoryModel(options.data);
}
}
}
function categoryModel(data) {
var self = this;
ko.mapping.fromJS(data, {}, self);
}

Answer 1

Guessing that you've moved on by now, but thought I'd offer a recommendation for others in a similar position.
Our solution to a similar situation borrows from the breeze.js TempHire sample solution which implements a client side repository/uow pattern. The solution uses an EntityMananagerProvider to manage multiple EntityManagers. The EntityMananagerProvider makes a single call for metadata, which is then used to create new child EntityManagers - satisfying your concern regarding multiple metadata calls. You can then use custom models/uow/repositories to extend the child manager for specific views.