the.railsi.st is Patrick Crowley.

I'm a Ruby developer and this blog is a record of my experiences using Ruby on Rails to build web apps.

I also run SD Ruby, a local Ruby group in San Diego known for its podcast.

Lots of folks use attachment_fu to handle image uploads. It handles all the dirty work of uploading files, integrates with Amazon S3, and even supports all the different image libraries.

Which is awesome... but it kinda sucks at validating files. Take a pretty typical Photo class:

class Photo < ActiveRecord::Base
  has_attachment :content_type => :image, 
                 :storage => :file_system, 
                 :max_size => 5.megabytes,
                 :resize_to => '320x200>',
                 :thumbnails => { :thumb => '100x100>', :widget => "262x262>" },
                 :processor => MiniMagick
  validates_as_attachment

end

What happens when you forget to select a file before uploading?

• Content type can't be blank
• Content type is not included in the list
• Size can't be blank
• Size is not included in the list
• Filename can't be blank

So, let's try uploading a Word document:

• Content type is not included in the list

Or a file that's too big:

• Size is not included in the list

Let's try it again, but in English:

class Photo < ActiveRecord::Base
  has_attachment :content_type => :image, 
                 :storage => :file_system, 
                 :max_size => 5.megabytes,
                 :resize_to => '320x200>',
                 :thumbnails => { :thumb => '100x100>', :widget => "262x262>" },
                 :processor => MiniMagick
  
  def validate
    errors.add_to_base("You must choose a file to upload") unless self.filename
    
    unless self.filename == nil
      
      # Images should only be GIF, JPEG, or PNG
      [:content_type].each do |attr_name|
        enum = attachment_options[attr_name]
        unless enum.nil? || enum.include?(send(attr_name))
          errors.add_to_base("You can only upload images (GIF, JPEG, or PNG)")
        end
      end
      
      # Images should be less than 5 MB
      [:size].each do |attr_name|
        enum = attachment_options[attr_name]
        unless enum.nil? || enum.include?(send(attr_name))
          errors.add_to_base("Images should be smaller than 5 MB in size")
        end
      end
        
    end
  end

end

To get started, let's drop the validates_as_attachment method. Or, more specifically, try extracting its useful parts into something more useful.

Since we're dropping attachment_fu's validations, we need to roll our own validations for the Photo class. You can do this by declaring a validate method in your class, and adding appropriate logic.

We can also use errors.add_to_base to get total control over your validation messages. By default, Rails pair the model attribute name with an error message ("person" + "is missing an ear"), but sometimes this can lead to awkward phrases ("person is empty").

You'll need to custom this for your application, of course, but this post should give you some examples.

(I'm planning to follow this blog post up with a series of posts about improving validation messages.)