How to hide parts of the view given a user role on Rails 4

Question

I'm trying to hide parts of my views depending on the User role.

So let's say I want only admins to be able to destroy Products. Besides the code in the controller for preventing regular users from destroying records, I would do the following in the view:

<% if current_user.admin? %>
  <%= link_to 'Delete', product, method: :delete %>
<% end %>

The previous code works, but it's prone to errors of omission, which may cause regular users to see links to actions they are not allowed to execute.

Also, if I decide later on that a new role (e.g. "moderator") can delete Products, I would have to find the views that display a delete link and add the logic allowing moderators to see it.

And if there are many models that can be deleted only by admin users (e.g. Promotion, User) maitenance of all the ifs would be pretty challenging.

Is there a better way of doing it? Maybe using helpers, or something similar? I'm looking for something maybe like this:

<%= destroy_link 'Delete', product %> # Only admins can see it
<%= edit_link 'Edit', promotion %> # Again, only admins see this link
<%= show_link 'Show', comment %> # Everyone sees this one

I found these two questions that are similar to mine, but none of them answered my question:

Show and hide based on user role in rails

Ruby on Rails (3) hiding parts of the view

Allround

Answer 1

I strongly recommend pundit.

It allows you to create "policies" for each model. For your Product model you might have a ProductPolicy that looks something like this

class ProductPolicy < ApplicationPolicy
  def delete?
    user.admin?
  end
end

In your view you can do something like this

<% if policy(@post).delete? %>
  <%= link_to 'Delete', product, method: :delete %>
<% end %>

If later on you want to add a moderator role, just modify the policy method

class ProductPolicy < ApplicationPolicy
  def delete?
    user.admin? || user.moderator?
  end
end

Pegram

+1 for pundit; comparing to "mainstream" CanCan easier to understand as explicit, same ease of use in views and controllers logic, and much more flexible (not tricky at all when used along with rolify) Strongly recommended here as well! – Smitten

Chose this one as correct answer. I didn't like my own answer very much. :P – Allround

Answer 2

So I kind of figured a way to move the IFs out of the view. First, I override the link_to helper in my application_helper.rb:

def link_to(text, path, options={})
  super(text, path, options) unless options[:admin] and !current_user.admin?
end

Then on my views I use it as:

<%= link_to 'Edit Product', product, admin: true, ... %>

This prevents regular users from seeing admin links, but for other html tags with content inside, such as divs, tables etc., an if would still be needed.

Allround

Answer 3

CanCan is another gem that lets you define "Abilities" per user role. In views you can use something like if can? :delete, @post to check if the user may delete that specific post.

Casavant

Answer 4

Using the CanCan and Role gems, what is still needed is a way to Check The Route and see if "current_user" has permissions to access that Route based on their role(s) - then show/hide based on that.

This saves the user clicking on things and getting told they cannot see it - or us having to write per-item "if" logic specifying what roles can see what list-items (which the customer will change periodically, as roles are changed/refined) around every single link in one's menu (consider a bootstrap menu with 50+ items nested in groups with html formatting, etc), which is insane.

If we must put if-logic around each menu-item, let's use the exact same logic for every item by checking the role/permissions we already defined in the Ability file.

But in our menu-list, we have route-helpers - not "controller/method" info, so how to test the user's ability to hit the controller-action specified for the "path" in each link?

To get the controller and method (action) of a path (my examples use the 'users_path' route-helper) ...

Rails.application.routes.recognize_path(app.users_path)
        => {:controller=>"users", :action=>"index"}

Get just the controller-name

    Rails.application.routes.recognize_path(app.users_path)[:controller]
        => "users"

Ability uses the Model for its breakdown, so convert from controller name to it's model (assuming default naming used) ...

    Rails.application.routes.recognize_path(app.users_path)[:controller].classify
        => "User"

Get just the action-name

    Rails.application.routes.recognize_path(app.users_path)[:action]
        => "index"

And since the "can?" method needs a Symbol for the action, and Constant for the model, for each menu-item we get this:

    path_hash = Rails.application.routes.recognize_path(app.users_path)
    model = path_hash[:controller].classify.constantize
    action = path_hash[:action].to_sym

Then use our existing Abilty system to check if the current_user can access it, we have to pass the action as a symbol and the Model as a constant, so ...

    <% if can? action model %>
        <%= link_to "Users List", users_path %>
    <% end %>

Now we can change who can see this resource and link from the Ability file, without ever messing with the menu, again. But to make this a bit cleaner, I extracted out the lookup for each menu-item with this in the app-controller:

def get_path_parts(path)
  path_hash = Rails.application.routes.recognize_path(path)
  model_name = path_hash[:controller].classify.constantize
  action_name = path_hash[:action].to_sym
  return [model_name, action_name]
end
helper_method :get_path_parts

... so I could do this in the view (I took out all the html-formatting from the links for simplicity, here):

<% path_parts = get_path_parts(users_path); if can?(path_parts[1], path_parts[0]) %>
    <%= link_to "Users Listing", users_path %>
<% end %>

... and to make this not take all day typing these per-menu-item if-wraps, I used regex find/replace with capture and wildcards to wrap this around every list-item in the menu-item listing in one pass.

It's far from ideal, and I could do a lot more to make it much better, but I don't have spare-time to write the rest of this missing-piece of the Role/CanCan system. I hope this part helps someone out.

Circumvallate