How do i add an active class to a dynamic link? - ruby-on-rails

Question

I have a sidebar that holds a list of posts. I need the corresponding post on my sidebar to have an active class. What i have currently does not work so what is the best way to do this?
def is_active?(path)
current_page?(path) ? "active" : ""
end
<% #posts.each do |post| %>
<%= link_to post.title, post, class: is_active?(posts_path) %>
<% end %>

Answer 1

As I said in my comment, methods ending by ? should return a boolean value. If you decide to go against the convention this will make things harder for us.
I suggest you actually use an active_link_to like it is explained in that question.
However the main problem was that you didn't generate the URL properly for each post :
is_active?(posts_path)
The posts_path is the path to the index and not the individual post resource. You should use something like post_path(post)
You want to do something like this :
First your is_active? method, because it has a ? should return a boolean
def is_active?(path)
current_page?(path)
end
Then you can use it this way (you need to get the URL of the post using the post_path(post) helper)
<% #posts.each do |post| %>
<%= link_to post.title, post, class: ('active' if is_active?(post_path(post))) %>
<% end %>
EDIT : because is_active? does the same thing as current_page? you should simply replace the is_active? code by an alias declaration
alias :is_active? current_page?

Answer 2

I had to develop such a solution some years before. I implemented the following as helper methods to detect an active link. Be aware that this is not the best solution I think. I had to provide a full url. Fell free to edit the code to use a path or a parameter hash instead.
# Returns true or false if the page is displayed that belongs to the given url.
def link_selected?(url)
request_method = request.method.to_sym
begin
url_params = Revolution::Application.routes.recognize_path(
url, {:method=>request_method}
)
rescue Exception => e
{}
end
begin
request_params = Revolution::Application.routes.recognize_path(
request.url, {:method=>request_method}
)
rescue
{}
end
return true if url_params == request_params
return false
end
def is_active?(url)
return link_selected?(url) ? 'active' : nil
end