如何重构条件语句？

Question

I'm on Rails 4 and Im using devise for user management. I have a simple conditional statement in a show view like this

<% if user_signed_in? %>
    <%= link_to "Checkout", user_cart_path(current_user,@cart), method: :patch %>
<% else %>
    <%= link_to "Checkout", signin_path %>
<% end %>

I want to clean up my view and add make the conditional a method.

I have tried adding the method

def checkout_link(current_user)
    if user_signed_in?
        link_to "Checkout", user_cart_path(current_user, self), method: :patch
    else 
        link_to "Checkout", signin_path
    end
end

to my cart model, and replaced the conditional in my show cart view to

<%= @cart.checkout_link(current_user) %>

When I load the cart show page, I get an error

undefined method `user_signed_in?' for #<Cart:0x007fd015525228>

What am I doing wrong? Thanks.

Answer 1

The thing you are doing wrong is concerning your model with the view. This should not be done.

You should place the checkout_link in a view helper method. This will clean up your view, and keep the model only concerned about the data it contains.

Though, in this case, I would just have a single link that leads to the checkout, and if the user is not signed in, have a before_filter redirect them to sign in.

Answer 2

You have two options, you can either add to the view helper or use a decorator.

1. If you add the method to the view, it would look something like this:

     def checkout_link(cart) if user_signed_in? link_to "Checkout", user_cart_path(current_user,cart), method: :patch else link_to "Checkout", signin_path end end 

2. "The decorator wraps the model, and deals only with presentational concerns. In the controller, you decorate the article before handing it off to the view." ¹ If you would like to use a decorator, check out Ryan Bates' Railscast on them: using an existing gem or creating a decorator from scratch .

¹ Quoted from the Draper gem's README. https://github.com/drapergem/draper

Answer 3

You're almost there. You want your checkout_link method to be a "helper method" in a helper file, not in your model file. So, create a file named app/helpers/carts_helper.rb and move your checkout_link method there. Methods in helper files are available to views and controllers.

When I was just learning my way around Rails, I would do:

rails generate scaffold Dummy

specifically to see what files it generated, including helper files. This might be a good place to start.