Models

class Collection < ActiveRecord::Base

  belongs_to :profile
  has_many :projects
  has_one :thumbnail, class_name: "item", as: :thumbnailable
  attr_accessible :name, :description
  attr_accessor :image

  validates :name, uniqueness: { scope: :profile_id }, length: { minimum: 1, maximum: 100 }, allow_blank: false
  validates :description, length: { minimum: 5, maximum: 1000 }, allow_blank: true

  def image
    unless self.projects == nil
      self.projects.first.image
    else
      nil
    end
  end
end

class Project < ActiveRecord::Base
  belongs_to :collection
  has_many :items
  has_one :item, as: :image

  attr_accessible :name, :description, :items, :links
  attr_accessor :image

  serialize :links

  validates :name, uniqueness: { scope: :collection_id }, length: {minimum: 1, maximum: 20}, allow_blank: false
  validates :description, length: {minimum: 5, maximum: 200}, allow_blank: true

  def image
    unless self.items == nil
      self.items.first.image
    else
      nil
    end
  end
end

Trace

Trace with raise self.id.inspect - ln 18

ActionView::Template::Error (undefined method `id' for #<#<Class:0x00000006b914b8>:0x007f26ec91f518>):
    15:     - gallery.each do |gallery_item|
    16:       %li.span2{ id: "#{new_sibling}_#{gallery_item.id}" }
    17:         .thumbnail
    18:           - raise self.id.inspect
    19:           - if gallery_item.image
    20:             = image_tag gallery_item.image.url(:medium), { class: ["img-rounded"] }
    21:           - else
  app/views/layouts/_gallery.html.haml:18:in `block in _app_views_layouts__gallery_html_haml__1575251927046492898_56927680'
  app/views/layouts/_gallery.html.haml:15:in `_app_views_layouts__gallery_html_haml__1575251927046492898_56927680'
  app/views/users/show.html.haml:1:in `_app_views_users_show_html_haml__2844021620757440522_48447860'

--------------------------------------------

Started GET "/" for 127.0.0.1 at 2013-04-22 22:13:36 -0700
Processing by UsersController#show as HTML
  User Load (0.2ms)  SELECT "users".* FROM "users" WHERE "users"."id" = 2 LIMIT 1
  Profile Load (0.2ms)  SELECT "profiles".* FROM "profiles" WHERE "profiles"."user_id" = 2 LIMIT 1
  Collection Load (0.2ms)  SELECT "collections".* FROM "collections" WHERE "collections"."profile_id" = 2
  Project Load (0.1ms)  SELECT "projects".* FROM "projects" WHERE "projects"."collection_id" = 7
  Item Load (0.1ms)  SELECT "items".* FROM "items" WHERE "items"."project_id" = 2
  Project Load (0.1ms)  SELECT "projects".* FROM "projects" WHERE "projects"."collection_id" = 8
  Item Load (0.1ms)  SELECT "items".* FROM "items" WHERE "items"."project_id" = 3
  Rendered layouts/_gallery.html.haml (9.3ms)
  Rendered users/show.html.haml within layouts/application (9.9ms)
Completed 500 Internal Server Error in 14ms

ActionView::Template::Error (undefined method `image' for nil:NilClass):
    15:     - gallery.each do |gallery_item|
    16:       %li.span2{ id: "#{new_sibling}_#{gallery_item.id}" }
    17:         .thumbnail
    18:           - if gallery_item.image
    19:             = image_tag gallery_item.image.url(:medium), { class: ["img-rounded"] }
    20:           - else
    21:             %img{:src => "/assets/empty.jpg", :alt => "generic"}/
  app/models/project.rb:15:in `image'
  app/models/collection.rb:13:in `image'
  app/views/layouts/_gallery.html.haml:18:in `block in _app_views_layouts__gallery_html_haml___3765302753760464732_70071251215420'
  app/views/layouts/_gallery.html.haml:15:in `_app_views_layouts__gallery_html_haml___3765302753760464732_70071251215420'
  app/views/users/show.html.haml:1:in `_app_views_users_show_html_haml___3576415342936073813_65436800'

Visual trace

Trace with raise self.id.inspect - ln 18

ActionView::Template::Error (undefined method `id' for #<#<Class:0x00000006b914b8>:0x007f26ec91f518>):
    15:     - gallery.each do |gallery_item|
    16:       %li.span2{ id: "#{new_sibling}_#{gallery_item.id}" }
    17:         .thumbnail
    18:           - raise self.id.inspect
    19:           - if gallery_item.image
    20:             = image_tag gallery_item.image.url(:medium), { class: ["img-rounded"] }
    21:           - else
  app/views/layouts/_gallery.html.haml:18:in `block in _app_views_layouts__gallery_html_haml__1575251927046492898_56927680'
  app/views/layouts/_gallery.html.haml:15:in `_app_views_layouts__gallery_html_haml__1575251927046492898_5

Original exception tripped on line 19 of the above. "image" no method error. This collection currently has no Projects.

class Collection < ActiveRecord::Base

  belongs_to :profile
  has_many :projects
  has_one :thumbnail, class_name: "item", as: :thumbnailable
  attr_accessible :name, :description
  attr_accessor :image

  validates :name, uniqueness: { scope: :profile_id }, length: { minimum: 1, maximum: 100 }, allow_blank: false
  validates :description, length: { minimum: 5, maximum: 1000 }, allow_blank: true

  def image
    unless self.projects = nil
      self.projects.first.image
    else
      nil
    end
  end
end