Paper Clip Gem

Paper Clip Gem - Review

https://github.com/thoughtbot/paperclip


Paperclip is a gem used for attaching to Rails applications.

	class UserPhoto < ActiveRecord::Base
	belongs_to :user
	has_attached_file :photo, :styles =>
	{ :medium => "300>x300", :thumb => "200x200#" },
	:default_url => "assets/images/:style/missing.png"
	validates :user_id, presence: true
	validates :caption, length: { maximum: 140 }
	validates :photo_width, presence: true
	validates :photo_height, presence: true
	# Validations for Photo's
	validates :photo, presence: true
	# Don't let people upload Giant phot's and charge alot of out AWS account
	validates_attachment_size :photo, :less_than => 5.megabytes
	# Only let people uplad a photo
	validates_attachment_content_type :photo,
	:content_type => ['image/jpeg', 'image/png', 'image/jpg']
	after_post_process :save_image_dimensions
	def save_image_dimensions
	geo = Paperclip::Geometry.from_file(photo.queued_for_write[:original])
	self.photo_width = geo.width.to_i
	self.photo_height = geo.height.to_i
	end
	end

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<%= image_tag @user.user_photo.url %>
<%= image_tag @user.user_photo.url(:medium) %>
<%= image_tag @user.user_photo.url(:thumb) %>

Important Finds

:thumb => "200x200#"
The # signifies that this image is going to be saved as as a square on the inside of the photo. This is very useful for user profile pictures.

:medium => "300>x300"
This ensures that the image will have a a width greater than 300 px. 

Profile Pictures

User has_many UserPhotos

- I started by saving a bolean field on the UserPhoto to check if there is a default photo.
- I later found out that it is better to save a link on the user model

	class AddDefaultPhotoIdToUsers < ActiveRecord::Migration
	def change
	add_column :users, :default_photo_id, :integer
	remove_column :user_photos, :default_photo
	end
	end

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	def get_default_photo
	self.user_photos.find_by_id(default_photo_id)
	end

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How to Link to AWS Account

- It is a a bad idea to save images to the project. Amazon Web Server and Heroku work well together in order to save files at a cheap fast cost.

https://devcenter.heroku.com/articles/paperclip-s3

Class Instance Variables

Use Class instance Variables

We all know that class variables such as @@ are dangerous to use due to their leaky inheritance.

	class Presentaion < Document
	@@default_font = :ariel
	def self.default_font=(font)
	@@default_font=(font)
	end
	def default_font
	@@default_font
	end
	end
	class Resume < Document
	@@default_font = :nimbus
	def self.default_font=(font)
	@@default_font=(font)
	end
	def default_font
	@@default_font
	end
	end
	class Document
	@@default_font = :times ##LEAKY INTHERITANCE HERE
	end
	require 'document'
	require 'resume' # Rewrite class variable
	require 'presentation' # Rewrite class viable
	##THE FIX
	# As an alternative we can use...
	# 1. Use class variables with this in mind
	# 2. Use CONSTANTS
	# 3. Open up the Singleton Class
	class Presentaion < Document
	@default_font = :ariel
	class << self
	attr_accessor :default_font
	end
	end
	class Resume < Document
	@default_font = :nimbus
	class << self
	attr_accessor :default_font
	end
	end
	class Document
	@default_font = :times
	class << self
	attr_accessor :default_font
	end
	end

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<script src="https://gist.github.com/surgentt/9464842.js"></script>class Presentaion < Document


WHAT IS GOING ON HERE

 The class << self syntax opens up a classes singleton class.
  This allows you to specialize the behavior of methods called on that specific object.

http://stackoverflow.com/questions/2505067/class-self-idiom-in-ruby

Object
    ^
     |
  <Singleton Class>
    ^
    |
Instance

Singleton Method is a method that is defined for exactly one object instance.


The <Singleton Class> is only invoked when it is filled with something.

  - An example of this is a method on an instance variable.

hand_built_stub_printer = Object.new def hand_built_stub_printer.avaiable? true end