Carrierwaveの導入

インストール

terminal

brew install imagemagick

Gemfile

gem 'carrierwave'
gem 'mini_magick'

terminal

$ bundle install
$ rails g uploader image

Messageモデルに、image_uploaderをマウントする

app/models/message.rb

class Message < ApplicationRecord
  mount_uploader :image, ImageUploader
end

app/uploaders/image_uploader.rb

class ImageUploader < CarrierWave::Uploader::Base
  # Include RMagick or MiniMagick support:
  # include CarrierWave::RMagick
  include CarrierWave::MiniMagick
  # storage :fog
  process resize_to_fit: [800, 800]
end