使用attachment_fu上传图像

按照说明一步一步来，首先声明了一个model，用来保存图片信息，顺便在controller中实现图片上传，显示等功能，定义的model如下：

ruby 代码

class Upfile < ActiveRecord::Base
  has_attachment :content_type=>:image,:max_size=>2.megabyte,:thumbnails=>{:small=>'200x200>', :middle=>'400x400>'},:storage=>:db_file
  validates_as_attachment
end

这里我没有如例子给出的一般采用文件系统，而是使用了数据库来保存图像（如果需要保存在数据库中，需要另外定义一个model和一个数据表，Mode名字叫做DbFile)。各个参数的意义如下：

  This method accepts the options in a hash:
    :content_type     # Allowed content types.
                      # Allows all by default.  Use :image to allow all standard image types.
    :min_size         # Minimum size allowed.
                      # 1 byte is the default.
    :max_size         # Maximum size allowed.
                      # 1.megabyte is the default.
    :size             # Range of sizes allowed.
                      # (1..1.megabyte) is the default.  This overrides the :min_size and :max_size options.
    :resize_to        # Used by RMagick to resize images.
                      # Pass either an array of width/height, or a geometry string.
    :thumbnails       # Specifies a set of thumbnails to generate.
                      # This accepts a hash of filename suffixes and RMagick resizing options.
                      # This option need only be included if you want thumbnailing.
    :thumbnail_class  # Set which model class to use for thumbnails.
                      # This current attachment class is used by default.
    :path_prefix      # path to store the uploaded files.
                      # Uses public/#{table_name} by default for the filesystem, and just #{table_name} for the S3 backend. 
                      # Setting this sets the :storage to :file_system.
    :storage          # Specifies the storage system to use..
                      # Defaults to :db_file.  Options are :file_system, :db_file, and :s3.
    :processor        # Sets the image processor to use for resizing of the attached image.
                      # Options include ImageScience, Rmagick, and MiniMagick.  Default is whatever is installed.
   

  Examples:
    has_attachment :max_size => 1.kilobyte
    has_attachment :size => 1.megabyte..2.megabytes
    has_attachment :content_type => 'application/pdf'
    has_attachment :content_type => ['application/pdf', 'application/msword', 'text/plain']
    has_attachment :content_type => :image, :resize_to => [50,50]
    has_attachment :content_type => ['application/pdf', :image], :resize_to => 'x50'
    has_attachment :thumbnails => { :thumb => [50, 50], :geometry => 'x50' }
    has_attachment :storage => :file_system, :path_prefix => 'public/files'
    has_attachment :storage => :file_system, :path_prefix => 'public/files',
                   :content_type => :image, :resize_to => [50,50]
    has_attachment :storage => :file_system, :path_prefix => 'public/files',
                   :thumbnails => { :thumb => [50, 50], :geometry => 'x50' }
    has_attachment :storage => :s3


接下来定义Model对应的Migration
Upfile:

ruby 代码

class CreateUpfiles < ActiveRecord::Migration
  def self.up
    create_table :upfiles do |t|
      t.column :size,:integer,:null=>false
      t.column :content_type,:string,:null=>false
      t.column :filename,:string,:null=>false
      t.column :height,:integer
      t.column :width,:integer
      t.column :parent_id,:integer
      t.column :thumbnail,:string
      t.column :db_file_id,:integer
    end
  end

  def self.down
    drop_table :upfiles
  end
end

DbFile:

ruby 代码

class CreateDbFiles < ActiveRecord::Migration
  def self.up
    create_table :db_files do |t|
      t.column :data, :binary
    end
  end

  def self.down
    drop_table :db_files
  end
end

各个字段对应的解释如下：
Fields for attachment_fu metadata tables...
  in general:
    size,         :integer  # file size in bytes
    content_type, :string   # mime type, ex: application/mp3
    filename,     :string   # sanitized filename
  that reference images:
    height,       :integer  # in pixels
    width,        :integer  # in pixels
  that reference images that will be thumbnailed:
    parent_id,    :integer  # id of parent image (on the same table, a self-referencing foreign-key).
                            # Only populated if the current object is a thumbnail.
    thumbnail,    :string   # the 'type' of thumbnail this attachment record describes. 
                            # Only populated if the current object is a thumbnail.
                            # Usage:
                            # [ In Model 'Avatar' ]
                            #   has_attachment :content_type => :image,
                            #                  :storage => :file_system,
                            #                  :max_size => 500.kilobytes,
                            #                  :resize_to => '320x200>',
                            #                  :thumbnails => { :small => '10x10>',
                            #                                   :thumb => '100x100>' }
                            # [ Elsewhere ]
                            # @user.avatar.thumbnails.first.thumbnail #=> 'small'
  that reference files stored in the database (:db_file):
    db_file_id,   :integer  # id of the file in the database (foreign key)
   
Field for attachment_fu db_files table:
  data, :binary # binary file data, for use in database file storage

搞定了数据库，接下来让我们回到controller，在UpfileController中定义几个方法：upload，showimage，image，upload用来控制上传文件，showimage用来显示一幅图片，image用来得到某幅图片数据。一下是三个action的代码：

ruby 代码

class UpfileController < ApplicationController
  def upload
    if request.post?
      @attachable_file = Upfile.new(params[:attachment_metadata])
      if @attachable_file.save
        flash[:notice] = 'Attachment was successfully created.'
        redirect_to :action=>:showimage,:id=>@attachable_file.attributes["id"]
      end
    end
  end

  def showimage
    @image = Upfile.find(:first,:conditions=>{:id=>params[:id],:parent_id=>nil})
  end

  def image
    @image = Upfile.find(:first,:conditions=>{:id => params[:id]})
    send_data(@image.db_file.data,:filename=>@image.attributes["filename"],:type=>@image.attributes["content_type"],:disposition=>"inline")
  end
end

upload.rhtml:

ruby 代码

<h1>Upfile#upload</h1>
<% form_for(:attachment_metadata, :url => {:action=>"upload"}, :html => {:multipart=>true}) do |form| -%>
select image to upload: <%= form.file_field :uploaded_data %><p>
<%= submit_tag "upload now" %>
<% end -%>

showimage.rhtml

ruby 代码

<% if @image -%>
  <% if @image.image? -%>
    <img src="<%= url_for(:action=>:image,:id=>@image.attributes["id"]) %>" />
  <% end -%>
<% end -%>

经过这样设置，在upload一个图像后，会自动转到刚上传图像显示的页面。

不过经过我现在实践，这个方法还有一些问题，主要就是读取数据库中图像时，若图像比较大，则只能读取前65535个字节的数据，另外，@image.db_file.data.class是string