Rails利用carrierwave上传图片

1.添加gem

gem 'carrierwave'
gem 'mini_magick' #不使用rmagick，占内存

2.bundle install

3.为users表添加一个avatar字段,也可以为其他名称，注意相应的代码修改

rails g migration add_avatar_to_users avatar:string
rake db:migrate

4.生成Avatar，跟你添加的字段相同

rails generate uploader Avatar #将会生成文件app/uploaders/avatar_uploader.rb

5.为user的model user.rb添加如下代码，使表之间关联

mount_uploader :avatar, AvatarUploader

6.接下来进行修改app/uploaders/avatar_uploader.rb，下面是一个例子

# encoding: utf-8

class AvatarUploader < CarrierWave::Uploader::Base
  include CarrierWave::MiniMagick #使用minimagick处理压缩图片，确保安装magickimage这个东东，ubuntu可以sudo apt-get install magickimage

  # 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  #定义上传到哪个文件夹下
    "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end

  def default_url  #可以定义默认图片，如过用户没有上传图片，则可以使用默认的图片
    "avatar/#{version_name}.png"
  end


#图片的处理，有不同版本大小，网站可以在不同的地方调用不同的图片大小
 version :normal do
    process :resize_to_fill => [48, 48]
  end

  version :small do
    process :resize_to_fill => [16, 16]
  end

  version :large do
    process :resize_to_fill => [64, 64]
  end

  version :big do
    process :resize_to_fill => [120, 120]
  end
  # Add a white list of extensions which are allowed to be uploaded.
  # For images you might use something like this:
#指定上传文件的格式
  def extension_white_list
    %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

7.如何在表单中上传

<%= form_for(@user) do |f| %>
  <div class="field">
    <%= f.file_field :avatar %>
    <%= f.hidden_field :avatar_cache %>
  </div>
...
<%end%>

8.如何显示图片

    <%= image_tag(@user.avatar_url(:large)) if @user.avatar %>#这里的:large就是指定图片的版本为large 64x64大小

详细查看carrierwave的reademe

9.上传远程图片

articles_controller添加：

private
    def article_params
      params.require(:article).permit(:title, :text, :article_image, :article_image_cache, :remote_article_image_url)
    end

views/articles/_form.html.erb:

<%= form_for @article, :html => {:multipart => true} do |f| %>
    <!--区别@article跟：article,@为资源-->
<% if @article.errors.any? %>
    <div id = "error_explanation"
    <h2>
      保存文章时出现<%= @article.errors.count %>个错误！
    </h2>
    <!-- 错误个数-->
    <ul>
      <% @article.errors.full_messages.each do |msg| %>
          <li><%= msg %></li>
      <% end %>
    </ul>
    </div>
<% end %>

<p>
  <%= f.label :title %><br>
  <%= f.text_field :title %>
</p>

<p>
  <%= f.label :text %><br>
  <%= f.text_area :text %>
</p>

<p>
<%= f.file_field :article_image %>
<%= f.hidden_field :article_image_cache %>
</p>

<p>
  <label>article_image URL:</label>
  <%= image_tag(@article.article_image_url) if @article.article_image? %>
  <%= f.text_field :remote_article_image_url %>
</p>
<!--添加上传远程图片功能-->
<p>
  <%= f.submit %>
</p>

<% end %>