No route matches {:action=>"show", :controller=>"users"} - ruby-on-rails

Question

I'm trying to implement a Twitter Boostrap login form, that's gonna be used on every page (because the navigation bar is a part of the layout).
However, when trying the code below I get the following error:
No route matches {:action=>"show", :controller=>"users"}
User controller:
class UsersController < ApplicationController
def index
#users = User.all
end
def show
...
end
def login
...
end
end
_navigation.html.erb:
<div class="dropdown-menu" style="padding: 15px; padding-bottom: 0px;">
<%= form_for("user", :url => user_path) do |f| %>
<%= f.label :email%>
<%= f.text_field(:email, :size => 30, :class => 'login_field', :placeholder => 'Användarnamn')%>
<%= f.label :password%>
<%= f.text_field(:password, :size => 30, :class => 'login_field', :placeholder => 'Lösenord')%>
<%= f.submit "Logga in", :class => 'login_submit btn btn-primary' %>
<% end %>
</div>
config/routes.rb:
get "home/index"
resources :users
resources :projects
resources :tickets
root :to => 'home#index'
rake routes (that has to do with users):
users GET /users(.:format) users#index
POST /users(.:format) users#create
new_user GET /users/new(.:format) users#new
edit_user GET /users/:id/edit(.:format) users#edit
user GET /users/:id(.:format) users#show
PUT /users/:id(.:format) users#update
DELETE /users/:id(.:format) users#destroy
I'm new to Rails but find it strange that it complains that the route doesn't exist because the action "show" is to be found inside the user controller.
The other thing I'm wondering about is why it looks for the action "show", while it should be "login" in this case?
Why is this happening and what shall I do?

Answer 1

your error is in this line
<%= form_for("user", :url => user_path) do |f| %>
user_path is expecting an id. if you change that to users_path, that should fix it but I don't think that's your intention.
UPDATE: to use the login action on the users controller, you need to update your routes
resources :users do
post :login, on: :collection, as: :login
end
passing the :as option creates a named_route for you called login_users_path which you can use on your form_for. and since we wanted to do a post, we also need to specify that in the form_for
<%= form_for("user", :url => login_users_path, :html => { :method => :post }) do |f| %>

Answer 2

Update your routes.rb to look like:
get "home/index"
resources :users do
post :login, :on => :collection
end
resources :projects
resources :tickets
root :to => 'home#index'
and in your view file change the form_for line to be:
<%= form_for("user", :url => login_users_path) do |f| %>

Answer 3

resources :users only adds default routes. If you want to add new action (other then defaults) you need to use 'collection. And you can specify the method get or post. After adding to routes.rb. You can get the path by running rake routes then you add the correct route in the action of form.
resources :users, :collection => {:login => :post}