How to attach a file/image in your data? Using paperclip in a rails application.

在 rails 裡有一個很好用的夾檔套件paperclip，今天就要來簡單介紹paperclip怎麼用．

首先要利用imagemagick套件，讓你的rails專案具有處理影像的能力．
Mac OS X
$ brew install imagemagick 
Linux distribution
$ sudo apt-get install imagemagick -y

然後在Gemfile中引用paperclip．
# Gemfile
...
gem "paperclip", git: "git://github.com/thoughtbot/paperclip.git"
...

記得bundle一下．
$ bundle install
接下來利用scaffold製作一個範例，在這個範例中我們要用paperclip幫這個使用者加上照片，paperclip會將照片資料記錄起來並將照片上傳到public資料夾內．
$ rails generate scaffold User name:string email:string tel:string 

生成附檔資料表
$ rails generate paperclip user avatar
修改 class AddAvatarToUsers < ActiveRecord::Migration[5.2]
  def up
   add_attachment :users, :avatar
  end

  def down
   remove_attachment :users, :avatar
  end
end
讓user model知道怎麼處理夾檔，可以上傳的檔案格式容量限制等都可以寫在這裡．
# app/models/user.rb 
class User < ActiveRecord::Base
 has_attached_file :avatar, styles: { medium: "300x300", thumb: "100x100" }   validates_attachment_content_type :avatar, content_type: /\Aimage\/.*\Z/ 
 # Validate filename 
 validates_attachment_file_name :avatar, matches: [/png\Z/, /jpe?g\Z/] 
 # Explicitly do not validate 
 do_not_validate_attachment_file_type :avatar 
end 

在view中怎麼用呢？可以透過Helpers!
<%= image_tag @user.avatar.url %> 
<%= image_tag @user.avatar.url(:medium) %> 
<%= image_tag @user.avatar.url(:thumb) %> 
修改_form.html.erb # app/views/users/_form.html.erb 
...
<%= form.file_field :avatar %>
  <% if @user.avatar? %>
  <%= image_tag @user.avatar.url(:thumb) %>
<% end %>
...

修改show.html.erb # app/views/users/show.html.erb 
...
<%= form.file_field :avatar %>
  <% if @user.avatar? %>
  <%= image_tag @user.avatar.url(:thumb) %>
<% end %>
...

修改users_controller.rb # app/controller/users/users_controller.rb
class UsersController < ApplicationController ...
 def user_params
  params.require(:user).permit(:name, :email, :tel, :avatar, :avatar_cache)
 end
...
end 發佈前記得rake資料庫一下
$ rake db:migrate