Problems with `linkTo` which uses `needs` in application controller/templates

[rlivsey]

tldr - fiddle me this: http://jsfiddle.net/rlivsey/bjfDk/

The app has a contextual navigation bar for the current project in the application template:

+------------------------------------------------+
|   {{#if currentProject}} project nav {{/if}}   |
|------------------------------------------------|
|+----------------------------------------------+|
||                                              ||
||                                              ||
||                {{outlet}}                    ||
||                                              ||
||                                              ||
|+----------------------------------------------+|
+------------------------------------------------+

This gets the currentProject from the projectController via needs:

App.ApplicationController = Ember.Controller.extend({
    needs: "project",
    currentProjectBinding: "controllers.project"    
});

However is seems that currentProject is always truthy and so the project navigation always appears (I assume because the controller exists, even though it has no content). Binding instead to controllers.project.content toggles as expected, but I don't think we should have to do that?

{{linkTo}}'s in the navigation bar in the application template using currentProject break in a number of ways:

1. the href doesn't update when currentProject changes, but the contents of the link do
2. clicking the links raises "Uncaught RangeError: Maximum call stack size exceeded"

The fiddle shows these issues in action: http://jsfiddle.net/rlivsey/bjfDk/

[sly7-7]

@rlivsey All the errors are as you say related to the fact that currentProject is an ObjectProxy.
In the if helper, you can also used currentProject.id, and in the linkTo, use currentProject.content.
But that's interresting, in fact I don't know what I would when I use needs... the controller itself or the proxied content ? If it's the controller, then explicitely using `currentProjectBinding: 'controllers.project.content' is fine for me.

Concerning the linkTo hrefs... the template should be rerendered in order to make the link up to date, I don't know if it's possible to do that automatically. Perhaps adding an observer in the linkTo helpr can be added if the context change...

[rlivsey]

@sly7-7 yeah it's mainly an issue with having to think about something I'm not sure you should have to think about!

If a proxy doesn't have content, does it exist? I wonder if the {{if}} helper should check if the object has content?

I've fixed the href issue by wrapping them in a {{with}} to force the block to be re-rendered, but I agree it would be good for that to happen automagically.

[AlexanderZaytsev]

I think having an isPresent property on an ObjectProxy will make sense.

That's how you do it in Rails. There, Post.limit(3) will always return true (since it's an ActiveRecord::Relation), so to check if there is actually any content, you need to call any? on it.

A bit unrelated question, why are using needs and currentProjectBinding together?

What about just using it this way?

App.ApplicationController = Ember.Controller.extend({
    needs: "project" 
});

{{#if controllers.project}} project nav {{/if}}

Am I missing something?

[rlivsey]

@AlexanderZaytsev isPresent makes sense and would be quite useful.

As for why the binding, controllers.project feels like it exposes the implementation detail to the template whereas currentProject is the concept I'm asking for and then it's up to whatever controller/view the template is bound to to get it for me. Basically feels more natural when writing the templates.

I can change the implementation from "controllers.project" to "controllers.project.content" in the controller and I don't have to update any of my templates.

I should probably make it a one way binding though as I'm never going to change it from this end.

[sly7-7]

@rlivsey Concerning the Uncaught RangeError: Maximum call stack size exceeded, it appears because clicking on the link cause the router to enter the project route with the projectContoller as context. Then in the model hook, the controller, (the projectController) itself sets its content property to itself...kaboom.

[rlivsey]

Looks like @wycats sorted the truthiness issue, cheers!

@sly7-7 ah that makes sense, I wonder if linkTo should try to detect if it's dealing with a ObjectProxy and try and grab the actual content instead? I assume it's not as simple as just checking for content because a proxy could be wrapped in another proxy, maybe recursively grab content until it reaches the actual object?

[wagenet]

@rlivsey Is there still an issue here?

[rlivsey]

I've update the fiddle to use the latest master of Ember, the {{#if currentProject}} now works to not show the block after fc56b1e, but doesn't seem to ever show now! If you select a project you'll see the block with {{#if currentProjectContent}} show but not the other one.

The link href's don't update when the project changes either.

[wagenet]

@machty, were you planning to submit a PR for this?

[wagenet]

@machty, nevermind, for some reason it's just tomhuda's commit showing up in your branch.

[wagenet]

The issue here is that the boundIf isn't watching for changes to isTruthy so it won't ever reflect the situation where those change. #2011 provides a possible fix for this.