Routing error No route matches id nil (Rails)

Question

I'm getting the following error on a page that contains a link to credit/edit an object:

Routing Error No route matches {:controller=>"connections", :action=>"edit", :id=>nil}

My app has user profile pages (#show action in users_controller.rb) with a link to create or edit an existing "connection" (a relationship between users like Facebook or LinkedIn). If the connection does not exist, the link will send the user to create a new connection. If the connection already exists, the link will send the user to edit the existing connection. My create functionality works fine. However, once the connection has been created, visiting the user page throws the routing error. It clearly does not like my link_to for the edit action.

Here is the link_to on the user page:

<% unless current_user == @user %>
<% if @contact.present? %>

<%= @user.first_name %> is your <%= @connection.description %> &nbsp;(<%= link_to "edit contact", { :controller => 'connections', :action => 'edit', :id => @connection.id} %> )

<% else %>

How do you know <%= @user.first_name %>? (<%= link_to "edit contact", { :controller => 'connections', :action => 'create', :user_id => @user.id }, :method => 'post' %> )

<% end %>

The error also specifically states that :id is set to nil (null). The problem must be here. How can I my app to refer to the correct connection? My instance variable should have done the trick.

Here's the connection controller:

class ConnectionsController < ApplicationController

def index
end

 def update
  @connection = current_user.connections.find(params[:id])
    if @connection.update_attributes(params[:connection])
      flash[:notice] = "Contact relationship updated"
      render 'activities'
    end
  end

  def edit
    @connection = current_user.connections.find(params[:id])
  end

  def create
    #@user = User.find(params[:user_id])
    @connection = current_user.connections.build(params[:connection])
    @user = User.find(params[:user_id])
    if @connection.save
      flash[:success] = "Contact relationship saved!"
    else
      render @user
    end
  end
end

And here's the User controller show action (where the link_to exists):

 def show
    @user = User.find(params[:id])
    @connection = current_user.connections.build(:otheruser_id => @user)
    @contact = current_user.connections.where(user_id: current_user, otheruser_id: @user)
  end

routes.rb:

authenticated :user do
    root :to => 'activities#index'
  end
  root :to => "home#index"
  devise_for :users, :controllers => { :registrations => "registrations" }
  resources :users do
    member do
      get :following, :followers, :posts, :comments, :activities, :works, :contributions, :connections
    end
  end
  resources :works do
    resources :comments
  end
  resources :relationships, only: [:create, :destroy]
  resources :posts
  resources :activities
  resources :reposts
  resources :comments do
    member do
      put :toggle_is_contribution
    end
    end
  resources :explore
  resources :connections

Any ideas on how to fix the link_to? Thanks!

EDIT 1: relevant rake routes:

 connections GET    /connections(.:format)                         connections#index
                               POST   /connections(.:format)                         connections#create
                new_connection GET    /connections/new(.:format)                     connections#new
               edit_connection GET    /connections/:id/edit(.:format)                connections#edit
                    connection GET    /connections/:id(.:format)                     connections#show
                               PUT    /connections/:id(.:format)                     connections#update
                               DELETE /connections/:id(.:format)                     connections#destroy

Answer 1

Your problem is in:

@connection = current_user.connections.build(:otheruser_id => @user)

That instantiates a connection object and assigns it to @connection. This object hasn't been saved, therefore it doesn't have an id. Conceptually it's wrong too, how can you edit something that doesn't exist yet? If you want to send the user to create a new connection, Connections#new is what you're after.