paperclip一些使用技巧

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一、关于styles设置，缩略图的切割策略
有两个符号，一个是‘#’，另一个是‘>’，说明如下：

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trailing #, thumbnail will be centrally cropped, ensuring the requested dimensions.
trailing >, thumbnail will only be modified if it is currently larger requested dimensions. (i.e. the :small thumb for a 120×80 original image will be unchanged)

还有其他的符号：
http://www.imagemagick.org/Usage/resize/

另外如果仅仅写“120x”生成的图片会缩略成120像素宽的图，高度进行自动调整
如果写"x80"生成的图片会缩略成80像素高的图，宽度自动调整

二、批量处理图片的task任务

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You can (re)generate your thumbnails en masse with Paperclip’s rake tasks. Using our example class above:

rake paperclip:refresh:thumbnails CLASS=User

or to refresh all of your defined styles in one go (:thumb, :small, :medium from the above example)

rake paperclip:refresh CLASS=User

and to refresh only missing styles:
a list of styles will be defined or updated in a file “/public/system/paperclip_attachments.yml”

rake paperclip:refresh:missing_styles

If you are using the gem required version of paperclip the rake tasks may not be auto-loaded, but you can copy them into your lib/tasks directory if needed.

If you need more manual control or have a lot of thumbnails and only want to process a few, you can use #reprocess! like so:

users_to_reprocess.each do |user|
  user.photo.reprocess!
end