Rails - May 2006 - Can''t read from file field second time around

This piece of code takes an uploaded image and resizes it.  It''s a bit
nasty at the moment as I am still messing around with it.  What I can''t
understand is why it works for one iteration but then fails with:

zero-length blob not permitted `''

On the line:

img = Magick::Image.from_blob(self.image).first

I am basically doing this in the controller and it fails on the second
attempt - to resize and save the medium size image:

      if @params[:listing_image]
        @thumbnail_image = ListingImage.new(@params[:listing_image])
        @listing = @session[:listing]
        @thumbnail_image.listing_id = @listing.id
        @thumbnail_image.image_type = "thumb"
        @thumbnail_image.resize

        if @thumbnail_image.save!
          @med_image = ListingImage.new(@params[:listing_image])
          @med_image.listing_id = @listing.id
          @med_image.image_type = "med"
          @med_image.resize

          if @med_image.save!
            @lg_image = ListingImage.new(@params[:listing_image])
            @lg_image.listing_id = @listing.id
            @lg_image.image_type = "lg"
            @lg_image.resize

            if not @lg_image.save!
              @flash[:notice] = "Large size image could not be saved"
            end
          else
            @flash[:notice] = "Medium size image could not be saved"
          end
        else
          @flash[:notice] = "Thumbnail image could not be saved"
        end
      else
        @flash[:notice] = "No image was uploaded"
      end


Here is the offending code from the model:

def listing_image=(image_field)
    self.image = image_field.read
    self.content_type = image_field.content_type.chomp
  end

  def resize
    img = nil
    img = Magick::Image.from_blob(self.image).first
    img.format = "JPG"

    case self.image_type
      when "thumb"
        img.strip!.change_geometry("120x120!") { |cols, rows, img|
img.resize!(cols, rows) }
      when "med"
        img.strip!.change_geometry("320x320>") { |cols, rows, img|
img.resize!(cols, rows) }
      when "lg"
        img.strip!.change_geometry("640x480>") { |cols, rows, img|
img.resize!(cols, rows) }
      else
        raise "Unknown image type
''#{self.image_type}''"
    end

    self.width = img.columns
    self.height = img.rows
    self.image = img.to_blob
    img = nil
    GC.start
  end

What stupidity have I done here?

Thanks,

Matt.

On May 30, 2006, at 2:54 PM, Matthew Law wrote:
> This piece of code takes an uploaded image and resizes it.  It''s a
bit
> nasty at the moment as I am still messing around with it.  What I  
> can''t
> understand is why it works for one iteration but then fails with:
>
> zero-length blob not permitted `''
>
> On the line:
>
> img = Magick::Image.from_blob(self.image).first
>
> I am basically doing this in the controller and it fails on the second
> attempt - to resize and save the medium size image:
>
>         @thumbnail_image.resize
>           @med_image.resize
>             @lg_image.resize
>
> Here is the offending code from the model:
>
>   def resize
>     img = nil
>     img = Magick::Image.from_blob(self.image).first
>
> What stupidity have I done here?
You forgot to rewind.

-- 
Eric Hodel - drbrain@segment7.net - http://blog.segment7.net
This implementation is HODEL-HASH-9600 compliant

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