Railsで画像を簡単にアップロードする方法CarrierWaveを使う【初心者向け】

gem 'carrierwave'
gem 'mini_magick'

$ convert -version

Version: ImageMagick 6.9.7-4 Q16 x86_64 20170114 http://www.imagemagick.org
Copyright: © 1999-2017 ImageMagick Studio LLC

$ sudo apt-get -y install imagemagick

$ bundle

$ rails g scaffold upload image:string title:text body:string
$ rails g uploader images
$ rails db:migrate

class Upload < ApplicationRecord
  mount_uploader :image, ImagesUploader
end

class UploadsController < ApplicationController
  before_action :set_upload, only: [:show, :edit, :update, :destroy]

  # GET /uploads
  # GET /uploads.json
  def index
    @uploads = Upload.all
  end

  # GET /uploads/1
  # GET /uploads/1.json
  def show
  end

  # GET /uploads/new
  def new
    @upload = Upload.new
  end

  # GET /uploads/1/edit
  def edit
  end

  # POST /uploads
  # POST /uploads.json
  def create
    @upload = Upload.new(upload_params)

    respond_to do |format|
      if @upload.save
        format.html { redirect_to @upload, notice: 'Upload was successfully created.' }
        format.json { render :show, status: :created, location: @upload }
      else
        format.html { render :new }
        format.json { render json: @upload.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /uploads/1
  # PATCH/PUT /uploads/1.json
  def update
    respond_to do |format|
      if @upload.update(upload_params)
        format.html { redirect_to @upload, notice: 'Upload was successfully updated.' }
        format.json { render :show, status: :ok, location: @upload }
      else
        format.html { render :edit }
        format.json { render json: @upload.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /uploads/1
  # DELETE /uploads/1.json
  def destroy
    @upload.destroy
    respond_to do |format|
      format.html { redirect_to uploads_url, notice: 'Upload was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_upload
      @upload = Upload.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def upload_params
      params.require(:upload).permit(:image, :title, :body)
    end
end

class ImagesUploader < 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/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end

  def extension_whitelist
    %w(jpg jpeg gif png)
  end

  process :resize_to_limit => [700, 700]

  version :thumb do
    process resize_to_fill: [100, 100]
  end
end

<%= form_with(model: upload, local: true) do |form| %>
  <% if upload.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(upload.errors.count, "error") %> prohibited this upload from being saved:</h2>

      <ul>
      <% upload.errors.full_messages.each do |message| %>
        <li><%= message %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= form.label :image %>
    <%= form.file_field :image %>
  </div>

  <div class="field">
    <%= form.label :title %>
    <%= form.text_field :title %>
  </div>

  <div class="field">
    <%= form.label :body %>
    <%= form.text_area :body %>
  </div>

  <div class="actions">
    <%= form.submit %>
  </div>
<% end %>

<p id="notice"><%= notice %></p>

<p>
  <strong>Image:</strong>
  <%#= @upload.image %>
  <%= image_tag @upload.image_url(:thumb ) if @upload.image.present? %>

</p>

<p>
  <strong>Title:</strong>
  <%= @upload.title %>
</p>

<p>
  <strong>Body:</strong>
  <%= @upload.body %>
</p>

<%= link_to 'Edit', edit_upload_path(@upload) %> |
<%= link_to 'Back', uploads_path %>