CarrierWave store the content type

carrierwave_content_type.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rails'
  gem 'carrierwave', github: 'carrierwaveuploader/carrierwave'
  gem 'sqlite3'
end

require 'active_record'
require 'carrierwave'
require 'carrierwave/orm/activerecord'
require 'minitest/autorun'
require 'logger'

ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)
ActiveRecord::Base.raise_in_transactional_callbacks = true

ActiveRecord::Schema.define do
  create_table :posts, force: true  do |t|
    t.string :image
    t.string :image_content_type
  end
end

class ImageUploader < CarrierWave::Uploader::Base
  process :save_content_type_in_model

  def save_content_type_in_model
    model.image_content_type = file.content_type if file.content_type
  end
end

class Post < ActiveRecord::Base
  mount_uploader :image, ImageUploader
end

class ContentTypeTest < Minitest::Test
  def test_content_type
    post = Post.new
    post.image = File.open('ruby-logo.png')
    post.save!

    assert_equal 'image/png', post.image_content_type
  end
end