undefined method paypal_url in Rails - ruby-on-rails

Question

I have a piece of code in Rails,
def create
#registration = Registration.new(registration_params)
if #registration.save
redirect_to #registration.paypal_url(registration_path(#registration))
else
render :new
end
end
I took it from tutorial. But I need just in this line:
#registration.paypal_url(registration_path(#registration))
Now, about my own controller, feed_controller, where
def create
#feed = Feed.new(check_params)
end
In the view erb file I put:
#feed.paypal_url(feed_path(#feed))
In my feed.rb (model):
def paypal_url(return_path)
values = {
business: "merchant#gotealeaf.com",
cmd: "_xclick",
upload: 1,
return: "#{Rails.application.secrets.app_host}#{return_path}",
invoice: id,
amount: course.price,
item_name: course.name,
item_number: course.id,
quantity: '1'
}
"#{Rails.application.secrets.paypal_host}/cgi-bin/webscr?" + values.to_query
end
Rake routes:
feed GET /:locale/feed(.:format) feed#index
feed#create POST /:locale/feed/create(.:format)
feed#new feed_new GET /:locale/feed/new(.:format)
feed#destroy feed_destroy GET /:locale/feed/destroy(.:format)
feed#edit feed_edit GET /:locale/feed/edit(.:format)
feed#update feed_update GET /:locale/feed/update(.:format)
But it prints the next error:
undefined method `paypal_url' for <#Feed::ActiveRecord_Relation:0x007fee24f5fc98>
How can I fix it? What is the problem?
UPDATE
def index
#current_user_is = current_user.email
session[:email] = #current_user_is
session[:id] = current_user.id
unless (current_user.member.present?)
#member = Member.new(:user_id => current_user.id)
#member.save()
redirect_to '/feed'
else
#new_feed = Feed.new
#feed = Feed.where(:member_id => current_user.member.id)
#category = Category.all
render 'home/uploads'
end
end

Answer 1

Simply use def self.paypal_url(return_path) instead of def paypal_url(return_path).
Explanation
You ran into your problem by defining a Class Method instead of an Instance Method, there's other posts discussing this.
The basic difference is, when defining:
def self.get_some_url
# code to return url of an instance
end
you can easily get the desired url of any objects, as in a view:
<% #feeds.each do |feed| %>
<%= feeds.get_some_url %>
<% end %>
Now calling Feed.get_some_url on the class would make no sense. Which url of the thousands would it call?
But there is a lot of use for class methods (where you define the method without self as you did)
def get_top_5
# code to return the top 5 most viewed feeds
end
Since this has nothing to do with a single instance, you define it for the entire Class. Leading to this call: Feed.get_top_5, which makes perfectly sense.
The second problem was not understanding the difference between where & find, this post will help you out with that.