How to improve and run a custom validation method?

I am using Ruby on Rails 3.0.9 and Paperclip 2.3. Since the Paperclip gem offers only two validation methods (validates_attachment_presence and validates_attachment_content_type) I开发者_JS百科 am trying to implement my custom validation methods.

In my model file I have just the following validation method

def validates_avatar(attribute_name, file)
  if file.nil? # file value is nil if no file is uploaded
    self.errors.add( "#{attribute_name}", "You must select a file" )
  else
    self.errors.add( "#{attribute_name}", "Avatar is an invalid image format") unless MIME_TYPES.include?(file.content_type)
    self.errors.add( "#{attribute_name}", "Avatar is too big" if ( ( file.size > AVATAR_FILE_MAX_SIZE.to_i ) || ( file.size == nil ) )
  end

  return self.errors.empty?
end

that I call from my controllers in this way:

if @user.validates_avatar(:avatar, params[:user][:avatar])
  ...
end

I would like to make the above validation to run\to trigger the same way of all others Ruby on Rails validation methods (eg: as-like validates :title, :presence => true works).

How can I do that and how can I improve the above code in order to handle avatar validations?

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It is already included in Paperclip and it do just the same job. so why do you want to repet it?

class Avatar < ActiveRecord::Base
  has_attached_file :file
  validates_attachment_presence :file
  validates_attachment_size :file, :less_than => 5.megabytes
  validates_attachment_content_type :file, :content_type => ['image/jpeg', 'image/png']
end

and never validate in Controller - it is Model job. Just

@user = User.new(params[:user])
@user.save

It won't save @user if @user.avatar won't pass validation

---

You should really move validations to a model. Here is an example:

validate :avatar_should_be_valid

def :avatar_should_be_valid
errors.add(:base, "avatar is invalid!") if...
end