Loaf does not work correctly with cancancan gem

[tomkr4l]

Describe the problem

When working with cancancan gem, loaf loading breadcrumbs and their paths before load_resource method is called.

Steps to reproduce the problem

class TopicsController < ApplicationController
  load_resource :project #cancacan method
  load_and_authorize_resource through: :project

  breadcrumb @project.name, [@project], only: :index
end

Actual behaviour

@project should be loaded before breadcrumb call, but instead I get NoMethodError undefined method `name' for nil:NilClass and @project is not loaded.

Expected behaviour

@project and @topics should be loaded before breadcrumb method call.

Notes

One method how to solve this problem is to move breadcrumb right inside method e.g.

def index
  breadcrumb @project.name, [@project], only: :index
end

This works fine, but It now allows dry code because I have to repeat same breadcrumbs in all methods where I need to use them.

Describe your environment

• OS version: Ubuntu 16.04
• Ruby version: 2.5.1
• Loaf version: 0.8.0
• Cancancan version: 2.2.0

[piotrmurach]

Hey Tomáš,

Thanks for using loaf!

I don't belive this is an issue with loaf or even connected to cancancan gem. Let me try to explain. First of all, let's forget about cancancan gem for a minute because it is not relevant to this discussion per say.

The breadcrumb at the controller level is a simple wrapper around before_action. Therfore, for the sake of simplicty, let's assume it means the same. Let's also assume that we have implemented our own load_resource method:

def load_resource
  @project = Project.find(params[:id])
end

Knowing the above, let's simplify your issue to the following:

class TopicsController < ApplicationController
  before_action :load_resource # loads @project similar to what cancancan gem would do
  before_action @project.name  # here @project is nil, because we're at class level!

  def index
     @project.name # this is fine since we're referencing an instance which was created
                   # during load_resource call
  end
end

Please read loaf documentation, in particular 2.1.1 controller section. In there you will see that you can evaluted breadcrumb name in the context of controller instance.

[jrochkind]

So would this work as:

class TopicsController < ApplicationController
  load_resource :project #cancacan method
  load_and_authorize_resource through: :project

  breadcrumb -> { @project.name }, -> { [@project] }, only: :index
end

[piotrmurach]

@jrochkind Provided that the proc is evaluated in the context of controller class instance then this would work.

[jrochkind]

which... it is, right? like, that's how loaf works?

[piotrmurach]

It boils down to Rails and before_actionsince breadcrumb call piggybacks on it. I don't remember off top of my head if that's the case or not.