[Ruby on Rails] How to use CarrierWave

What is Carrier Wave?

A gem that allows you to easily add file uploads.

Carrier Wave installation

After adding the following to Gemfile, execute the command to install the gem.

gem 'carrierwave'
$ bundle install

Creating an uploader

Running the rails g uploader uploader name command creates the app/uploaders/image_uploader.rb file. This time, the uploader name is image.

$ rails g uploader image

Linking with the model

mount_uploader: Uploader name, class name will be added to the associated model.

class Post < ApplicationRecord
  mount_uploader :image, ImageUploader

Edit controller

Create a controller to upload the image. Create as usual without being aware of uploading images. Since there are text and image columns, the strong parameters are described as follows.

class PostsController < ApplicationController

 def post_params
  params.permit(:image, :content)


Edit view

Create a form to upload the image. Create as usual without being aware of uploading images. For example, it looks like this.

<%= form_with url: "/posts/create" do |f| %>
  <div class="form">
    <%= f.label "Posting a photo" %><br>
    <%= f.file_field :image %><br>
    <%= f.text_area :content, value: @post.content %><br>
    <%= f.submit "Post" %>
<% end %>

When you upload an image using this form, the image will be saved in the public/uploads folder.

By adding <% if @ user.image?%>, You can check whether the image has been set and conditionally branch depending on whether the image is set or not.

Display the saved image

To display the saved image, call it with image_tag.

<%= image_tag @post.image_url %>

Adding if @ post.image? will prevent you from getting an error when there is no image.

<%= image_tag @post.image_url if @post.image? %>

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