days_controller.rb

class DaysController < ApplicationController
  
  before_filter :get_day, :only => [:show, :edit, :update, :destroy]
  
  def get_day
    @day = Day.find(params[:id])
  end
  
  def index
    @days = Day.all
  end
  
  def show
    @habit = @day.habit
  end

  def new
    @day = Day.new
  end

  def create
    @day = Day.new(params[:day])
    if @day.save
      redirect_to days_path
    else
      render "new"
    end
  end
  
  def edit
    @day = Day.find(params[:id])
  end
  
  def update
    if @day.update_attributes(params[:day])
      redirect_to days_path
    else
      render "edit"
    end
  end
  
  def destroy
    @day.destroy
    redirect_to days_path
  end
  
end

Error

No route matches {:action=>"show", :controller=>"habits", :day_id=>#<Day id: 4, wake: "7:30 am", sleep: "", created_at: "2012-09-09 20:11:48", updated_at: "2012-09-09 20:11:48">, :id=>nil}

Error!

No route matches {:action=>"show", :controller=>"habits", :day_id=>#<Day id: 4, wake: "7:30 am", sleep: "", created_at: "2012-09-09 20:11:48", updated_at: "2012-09-09 20:11:48">, :id=>nil}

habits_controller.rb

class HabitsController < ApplicationController
  
  before_filter :get_day
  
  def get_day
    @day = Day.find(params[:day_id])
  end
  
  def new
    @habit = @day.build_habit
  end
  
  def create
    @habit = @day.build_habit(params[:habit])
    if @habit.save
      redirect_to @day
    else
      render "day/show"
    end
  end
  
  def edit
    @habit = @day.habit
  end
  
  def update
    @habit = @day.habit
    if @habit.update_attributes(params[:habit])
      redirect_to @day
    else
      render "new"
    end
  end
  
  def destroy
    @habit = @day.habit
    @habit.destroy
    redirect_to @day
  end
  
end

index.html.erb

<h1>Life-ulator</h1>

<%= link_to "New Day", new_day_path %>
  
<table id="days-list">
  <thead>
    <tr>
	  <th>Date</th>
	  <th>Wake</th>
	  <th>Sleep</th>
	</tr>
  </thead>

  <% @days.each do |day| %>
 
  <tbody>
	<tr>
	  <td><%= day.created_at.strftime("%x")  %></td>
	  <td><%= day.wake  %></td>
	  <td><%= day.sleep  %></td>
	  <td><%= link_to "View", day_path(day) %></td>
	  <td><%= link_to "Edit", edit_day_path(day) %></td>
	  <td><%= link_to "Delete", day, :confirm => "Sure?", :method => :delete  %></td>
	</tr>
  </tbody>

  <% end %>
</table>

models

class Day < ActiveRecord::Base
  attr_accessible :sleep, :wake
  has_one :habit, :dependent => :destroy
end


class Habit < ActiveRecord::Base
  belongs_to :day
  attr_accessible :energy, :mood, :overall
end

routes.rb

LifeUlator::Application.routes.draw do

  root :to => "Days#index"
  
  resources :days do
    resources :habits
  end
  
end

show.html.erb

<h1><%= @day.created_at.strftime("%x")  %></h1>

<%= link_to "Back", days_path %>

<table id="days-list">
  <thead>
    <tr>
	  <th>Date</th>
	  <th>Wake</th>
	  <th>Sleep</th>
	</tr>
  </thead>
 
  <tbody>
	<tr>
	  <td><%= @day.created_at.strftime("%x")  %></td>
	  <td><%= @day.wake  %></td>
	  <td><%= @day.sleep  %></td>
	  <td><%= link_to "New Habits", new_day_habit_path(@day, @habit)%></td>
	  <td><%= link_to "Edit", edit_day_path(@day) %></td>
	  <td><%= link_to "Delete", @day, :confirm => "Sure?", :method => :delete  %></td>
	</tr>
  </tbody>

</table>

<table id="habits-list">
  <thead>
    <tr>
	  <th>Energy</th>
	  <th>Mood</th>
	  <th>Overall</th>
	  <td><%= link_to "Delete", [@day, @habit], :confirm => "Sure?", :method => :delete  %></td>
	</tr>
  </thead>

</table>