1. 이미지 업로드(동영상, 파일 업로드도 동일)

rails generate model UploadFile # 프로젝트/app/models/upload_file.rb가 생성됨.

# upload_file.rb
class UploadFile < ApplicationRecord
	mount_uploader :file, FileUploader
end

rails generate uploader File # 프로젝트/app/uploaders/file_uploader.rb가 생성됨.

#file_uploader.rb
Class FileUploader < CarrierWave::Uploader::Base
# Include RMagick or MiniMagick support:
  # include CarrierWave::RMagick
  # include CarrierWave::MiniMagick


  # Choose what kind of storage to use for this uploader:
  storage :file
  # storage :fog

  # Override the directory where uploaded files will be stored.
  # This is a sensible default for uploaders that are meant to be mounted:
  def store_dir
    "uploads/"
  end

  # Provide a default URL as a default if there hasn't been a file uploaded:
  # def default_url(*args)
  #   # For Rails 3.1+ asset pipeline compatibility:
  #   # ActionController::Base.helpers.asset_path("fallback/" + [version_name, "default.png"].compact.join('_'))
  #
  #   "/images/fallback/" + [version_name, "default.png"].compact.join('_')
  # end

  # Process files as they are uploaded:
  # process scale: [200, 300]
  #
  # def scale(width, height)
  #   # do something
  # end

  # Create different versions of your uploaded files:
  # version :thumb do
  #   process resize_to_fit: [50, 50]
  # end

  # Add a white list of extensions which are allowed to be uploaded.
  # For images you might use something like this:
  # def extension_whitelist
  #   %w(jpg jpeg gif png)
  # end

  # Override the filename of the uploaded files:
  # Avoid using model.id or version_name here, see uploader/store.rb for details.
  def filename
    "#{secure_token}.#{file.extension}" if original_filename.present?
  end

  protected
  def secure_token
    var = :"@#{mounted_as}_secure_token"
    model.instance_variable_get(var) or model.instance_variable_set(var, SecureRandom.uuid)
  end
end 

rails generate controller UploadFile # 프로젝트/app/controllers/upload_file_controller.rb가 생성됨.

#upload_file_controller.rb
class UploadFileController < ApplicationController
	skip_before_action :verify_authenticity_token # csrf_token
  
	def create
		uploaded = UploadFile.create(file: params[:file]) 
		render json:{
			'uploadPath': uploaded.file.url
		}
	end
end

rails generate migration AddFileToUploadFile file:string # UploadFile에 파일을 담을 'file' 필드 추가
rake db:migrate

#config/routes.rb
Rails.application.routes.draw do
	...
	resource :upload_file #라우터와 컨트롤러 연결
	...
end

#upload_file.rb

#file_uploader.rb