Rails Image Upload: Using CarrierWave

1. In Rails, add it to your Gemfile:

     gem 'carrierwave', '~> 2.0'

2. Start off by generating an uploader:  rails generate uploader Avatar

3. this should give you a file in:      app/uploaders/avatar_uploader.rb

4. Check out this file for some hints on how you can customize your uploader.
    It should look something like this:
    

     class AvatarUploader < CarrierWave::Uploader::Base
        storage :file
     end

5. Add a string column to the model you want to mount the uploader by creating 

    a migration:

      

      rails g migration add_avatar_to_users avatar:string

      rails db:migrate

6. Open your model file and mount the uploader:

     

    class User < ActiveRecord::Base
      mount_uploader :avatar, AvatarUploader
    end

7. 

   <div class="field col-lg-12 from-group">
      <%= form.label :image %>
      <%= form.file_field :image, :class => "form-control",:required=> true  %>
   </div>

8. <%= image_tag product.image.url(:thumb) %>  

9. Add gem "mini_magick" in your gemfile.

    link:= https://rubygems.org/gems/mini_magick/versions/4.5.1

  When you modify the image size then you add this code in   

    uploaders/image_uploader.rb file.

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


   version :medium do
      process resize_to_fill: [400,400]
    end

  version :project do
      process :resize_to_fill => [275, 180]
    end

    version :comment do
      process :resize_to_fill => [580, 0]
    end 

    version :projectimg do
      process resize_to_fit: [275,180]
      process :convert => :jpg  
    end

    version :featuredmd do
      process :resize_to_fill => [585, 350]
    end

    version :featuredsm do
      process :resize_to_fill => [400, 350]
    end

    version :topicbanner do
      process :resize_to_fill => [800, 350]
    end

    version :topicmd do
      process :resize_to_fill => [450, 350]
    end

    version :topiclg do
      process :resize_to_fill => [650, 350]
    end

    version :userbanner do
      process :resize_to_fill => [800, 350]
    end

10. Link:- https://github.com/carrierwaveuploader/carrierwave