CarrierWaveの使い方

Gemfile

gem 'carrierwave'

$ bundle install

uploaderを作成

$ rails g uploader image

app/uploaders/image_uploader.rbが作成される

image_uploader.rb

class ImageUploader < CarrierWave::Uploader::Base
  # リサイズしたり画像形式を変更するのに必要
  # 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/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  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:
  # アップロードできる拡張子を制限
  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
    "something.jpg" if original_filename
  end
end

画像用のカラムを追加
※今回はuserモデルに追加を想定

$ rails g migration add_image_to_user image:string

モデルに追加

user.rb

class User < ApplicationRecord
    mount_uploader :image, ImageUploader
end

permitにimageを追加

controller.rb

:image

入力側

edit.rb

    <%= f.label :顔画像 %>
    <%= f.file_field :image %>

表示側

show.rb

<img src="<%= @user.image %>" width="100">