routing/url mapping broken for link_to tag in rails app

Ive been trying to get this to work for 3 days now. I cant seem to understand why it doesn work. When the user clicks that link_to tag on the view it should execute the csv function in the controller. Instread I get an exception.

Here are the relevant files

Controller file: (users_controller.rb)

def csv 

end

(Routes.rb):

resources :users

View: (show.html.erb)

 <%= link_to 'Click HERE to open file', @user.image.url  %><br/><br/><br/>
 <%= label_tag(:q, "Parse CSV File:") %><br/>
 <%= link_to 'CSV', csv_user_path %>
 <% end %>

When I click on the "link_to 'CSV'.. tag above. It gives me this exception:

 NameError in Users#show 
 Showing /Users/AM/Documents/RailsWS/bmc_mam/app/views/users/show.html.erb where line #47 raised:
Extracted source (around line #47):

44:         
45:  <%= label_tag(:q, "Parse CSV File:") %><br/>
46:  
47: <%= link_to 'CSV', csv_user_path %>
48:             
49:         
50:

The browser URL is as follows when the exception occurs:

http://localhost:3000/users/28

Its clearly getting to the function but the URL mapping /routing is clearly messed up. I m wondering how to fix it.....Ive tried several approaches over the past few days, none seem to be working. This is the closest Ive gotten to making it work as in ...

Thanks in advance for your help.

After post answer posted below by @Gavin Miller:

I cahnged my routes.rb file to this:

get 'csv' => 'users#csv'
resources :users

Now Im getting this exception:

NameError in Users#show

Showing /Users/AM/Documents/RailsWS/bmc_mam/app/views/users/show.html.erb where line #47    raised:

undefined local variable or method `csv_user_path' for #<#  <Class:0x00000104e7f6f8>:0x00000103a23c68>

Extracted source (around line #47):

44:         
45:             <%= label_tag(:q, "Parse CSV File:") %><br/>
46:             
47:             <%= link_to 'CSV', csv_user_path %>
48:             
49:         
50:

Solution

Just declaring resources :users is only going to infer the 7 standard RESTful actions¹. if you want csv to be accepted as a route, you'll have to explicitly define it:

get 'csv' => 'controller#action'

where controller == users and action == csv.

Re-addressing the edited question... You'll need to pass a user object to the csv_user_path function:

<%= link_to 'CSV', csv_user_path(@user) %>

It also appears like you'd like the url to be associated with the user, so you can declare it as a member to get a url like: http://localhost:3000/users/28/csv for that result you can use this code:

resources :users do
  member do
    get 'csv'
  end
end

¹ RESTful actions are index, new, create, show, edit, update, destroy as seen in Rails Routing Guide