At which point does one fetch a Backbone Model on which a view depends?

Question

I seem to often end up in a situation where I am rendering a view, but the Model on which that view depends is not yet loaded. Most often, I have just the model's ID taken from the URL, e.g. for a hypothetical market application, a user lands on the app with that URL:

http://example.org/#/products/product0

In my ProductView, I create a ProductModel and set its id, product0 and then I fetch(). I render once with placeholders, and when the fetch completes, I re-render. But I'm hoping there's a better way.

Waiting for the model to load before rendering anything feels unresponsive. Re-rendering causes flickering, and adding "loading... please wait" or spinners everywhere makes the view templates very complicated (esp. if the model fetch fails because the model doesn't exist, or the user isn't authorized to view the page).

So, what is the proper way to render a view when you don't yet have the model?

Do I need to step away from hashtag-views and use pushState? Can the server give me a push? I'm all ears.

Loading from an already-loaded page:

I feel there's more you can do when there's already a page loaded as opposed to landing straight on the Product page.

If the app renders a link to a Product page, say by rendering a ProductOrder collection, is there something more that can be done?

<ul id="product-order-list">
  <li>Ordered 5 days ago. Product 0 <a href="#/products/product0">(see details)</a></li>
  <li>Ordered 1 month ago. Product 1 <a href="#/products/product1">(see details)</a></li>
</ul>

My natural way to handle this link-to-details-page pattern is to define a route which does something along these lines:

routes: {
  'products/:productid': 'showProduct'
  ...
}

showProduct: function (productid) {
  var model = new Product({_id: productid});
  var view = new ProductView({model: model});
  //just jam it in there -- for brevity
  $("#main").html(view.render().el);
}

I tend to then call fetch() inside the view's initialize function, and call this.render() from an this.listenTo('change', ...) event listener. This leads to complicated render() cases, and objects appearing and disappearing from view. For instance, my view template for a Product might reserve some screen real-estate for user comments, but if and only if comments are present/enabled on the product -- and that is generally not known before the model is completely fetched from the server.

Now, where/when is it best to do the fetch?

1. If I load the model before the page transition, it leads to straightforward view code, but introduces delays perceptible to the user. The user would click on an item in the list, and would have to wait (without the page changing) for the model to be returned. Response times are important, and I haven't done a usability study on this, but I think users are used to see pages change immediately as soon as they click a link.

2. If I load the model inside the ProductView's initialize, with this.model.fetch() and listen for model events, I am forced to render twice, -- once before with empty placeholders (because otherwise you have to stare at a white page), and once after. If an error occurs during loading, then I have to wipe the view (which appears flickery/glitchy) and show some error.

Is there another option I am not seeing, perhaps involving a transitional loading page that can be reused between views? Or is good practice to always make the first call to render() display some spinners/loading indicators?

Edit: Loading via collection.fetch()

One may suggest that because the items are already part of the collection listed (the collection used to render the list of links), they could be fetched before the link is clicked, with collection.fetch(). If the collection was indeed a collection of Product, then it would be easy to render the product view.

The Collection used to generate the list may not be a ProductCollection however. It may be a ProductOrderCollection or something else that simply has a reference to a product id (or some sufficient amount of product information to render a link to it).

Fetching all Product via a collection.fetch() may also be prohibitive if the Product model is big, esp. in the off-chance that one of the product links gets clicked.

The chicken or the egg? The collection.fetch() approach also doesn't really solve the problem for users that navigate directly to a product page... in this case we still need to render a ProductView page that requires a Product model to be fetched from just an id (or whatever's in the product page URL).

Answer 1

Alright, so in my opinion there's a lot of ways that you can fix this. I'll list all that I've thought of and hopefully one will work with you or at the very minimum it will inspire you to find your optimal solution.

I'm not entirely opposed to T J's answer. If you just go ahead and do a collection.fetch() on all the products when the website is loading (users generally expect there to be some load time involved) then you have all of your data and you can just pass that data round like he mentioned. The only difference between what he's suggesting and what I normally do is that I usually have a reference to app in all my views. So, for example in my initialize function in app.js I'll do something like this.

initialize: function() {
    var options = {app: this}

    var views = {
        productsView: new ProductsView(options)
    };

    this.collections = {
        products: new Products()
    }

    // This session model is just a sandbox object that I use
    // to store information about the user's session. I would
    // typically store things like currentlySelectedProductId
    // or lastViewedProduct or things like that. Then, I just
    // hang it off the app for ease of access.
    this.models = {
        session: new Session()
    }
}

Then in my productsView.js initialize function I would do this:

initialize: function(options) {
    this.app = options.app;

    this.views = {
        headerView: new HeaderView(options),
        productsListView: new ProductsListView(options),
        footerView: new FooterView(options)
    }; 
}

The subviews that I create in the initialize in productsView.js are arbitrary. I was mostly just trying to demonstrate that I continue to pass that options object to subviews of views as well.

What this does is allows every view, whether it be a top level view or deeply nested subview, every view knows about every other view, and every single view has reference to the application data.

These two code samples also introduce the concept of scoping your functionality as precise as you possibly can. Don't try to have a view that does everything. Pass functionality off to other views so that each view has one specific purpose. This will promote reuse of views as well. Especially complex modals.

Now to get back to the actual topic at hand. If you were going to go ahead and load all of the products up front where should you fetch them? Because like you said you don't want a blank page just sitting there in front of your user. So, my advice would be to trick them. Load as much of your page as you possibly can and only block the part that needs the data from loading. That way to the user the page looks like it's loading while you're actually doing work behind the scenes. If you can trick the user into thinking the page is steadily loading then they are much less likely to get impatient with the page load.

So, referencing the initialize from productsView.js, you could go ahead and let the headerView and footerView render. Then, you could do your fetch in the render of the productsListView.

Now, I know what you're thinking. Have I lost my mind. If you do a fetch in the render function then there's no way that the call will have time to return before we hit the line that actually renders the productsViewList template. Well, luckily there's a couple of ways around that. One way would be to use Promises. However, the way I typically do it is to just use the render function as its own callback. Let me show you.

render: function(everythingLoaded) {
    var _this = this;

    if(!!everythingLoaded) {
        this.$el.html(_.template(this.template(this)));
    }
    else {
        // load a spinner template here if you want a spinner

        this.app.collection.products.fetch()
            .done(function(data) {
                _this.render(true);
            })
            .fail(function(data) {
                console.warn('Error: ' + data.status);
            });
    }

    return this;
}

Now, by structuring our render this way the actual template won't load until the data has fully loaded.

While we have a render function here I want to introduce another concept that I use every where. I call it postRender. This is a function where I execute any code that depends on DOM elements being in place once the template has finished loading. If you were just coding a plain .html page then this is code that traditionally goes in the $(document).ready(function() {});. It may be worth noting that I don't use .html files for my templates. I use embedded javascript files (.ejs). Continuing on, the postRender function is a function that I have basically added to my boiler plate code. So, any time I call render for a view in the code base, I immediately chain postRender onto it. I also use postRender as a call back for itself like I did with the render. So, essentially the previous code example would look something like this in my code base.

render: function(everythingLoaded) {
    var _this = this;

    if(!!everythingLoaded) {
        this.$el.html(_.template(this.template(this)));
    }
    else {
        // load a spinner template here if you want a spinner

        this.app.collection.products.fetch()
            .done(function(data) {
                _this.render(true).postRender(true);
            })
            .fail(function(data) {
                console.warn('Error: ' + data.status);
            });
    }

    return this;
},

postRender: function(everythingLoaded) {
    if(!!everythingLoaded) {
        // do any DOM manipulation to the products list after 
        // it's loaded and rendered
    }
    else {
        // put code to start spinner
    }

    return this;
}

By chaining these functions like this we guarantee that they'll run sequentially.

=========================================================================

So, that's one way to tackle the problem. However, you mentioned that you don't want to necessarily load all of the products up front for fear that the request could take too long.

---

Side Note: You should really consider taking out any information related to the products call that could cause the call to take a considerable amount of time, and make the larger pieces of information a separate request. I have a feeling that users will be more forgiving about data taking a while to load if you can get them the core information really fast and if the thumbnails related to each product takes a little longer to load it shouldn't be then end of the world. That's just my opinion.

---

The other way to solve this problem is if you just want to go to a specific product page then just implement the render/postRender pattern that I outlined above on the individual productView. However note that your productView.js will probably have to look something like this:

initialize: function(options) {
    this.app = options.app;
    this.productId = options.productId;

    this.views = {
        headerView: new HeaderView(options),
        productsListView: new ProductsListView(options),
        footerView: new FooterView(options)
    }; 
}

render: function(everythingLoaded) {
    var _this = this;

    if(!!everythingLoaded) {
        this.$el.html(_.template(this.template(this)));
    }
    else {
        // load a spinner template here if you want a spinner

        this.app.collection.products.get(this.productId).fetch()
            .done(function(data) {
                _this.render(true).postRender(true);
            })
            .fail(function(data) {
                console.warn('Error: ' + data.status);
            });
    }

    return this;
},

postRender: function(everythingLoaded) {
    if(!!everythingLoaded) {
        // do any DOM manipulation to the product after it's 
        // loaded and rendered
    }
    else {
        // put code to start spinner
    }

    return this;
}

The only difference here is that the productId was passed along in the options object to the initialize and then that's pulled out and used in the .fetch in the render function.

========================================================================= In conclusion, I hope this helps. I'm not sure I've answered all of your questions, but I think I made a pretty good pass at them. For the sake of this getting too long I'm going to stop here for now and let you digest this and ask any questions that you have. I imagine I'll probably have to do at least 1 update to this post to further flush it out.

Answer 2

You started saying:

I have a listing of items in one Collection view

So what does a collection have..? Models..!

When you do collection.fetch() you retrieve all the models.

When the user selects an item, just pass the corresponding model to the item view, something like:

this.currentView = new ItemView({
  model: this.collection.find(id); // where this points to collection view
                            // and id is the id of clicked model
});

This way, there there won't be any delay/ improper rendering.

What if your collections end point returns huge volume of data..?

Then implement common practices like pagination, lazy loading etc.

---

I construct a Product model with the given ID

To me that sounds wrong. If you have a collection of products, you shouldn't be constructing such models manually.

Have the collection fetch your models before rendering the list view. This way all the problem you mentioned can be avoided.