Rails Carrierwave & Imagemagick, using conditions to resize image - ruby-on-rails

Question

I have been struggling to find any tutorial or question that explains how to upload image and resize it according to certain conditions provided by user.
I am easily able to upload and resize image using hard coded values, however I am stuck at using user provided parameters to be accessed from the Uploader.
I want the image to be resized to either 800x600 or 300x300 based on whether the user checks the image as Large or Small.
For that I have a boolean column named "large" in the model structure.
In the Uploader I am able to access model and its values easily in the store_dir block, but anywhere outside this block any model attribute returns as nil.
This is what I want to do:-
class BannerUploader < CarrierWave::Uploader::Base
include CarrierWave::MiniMagick
storage :file
def store_dir
"uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
end
resize_to_fit(800,600) if model.large==true
resize_to_fit(300,300) if model.large!=true
end
However this returns the error
undefined local variable or method `model' for BannerUploader:Class
How to go about this issue.

Answer 1

To process an original file you can specify custom method:
class BannerUploader < CarrierWave::Uploader::Base
include CarrierWave::MiniMagick
storage :file
def store_dir
"uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
end
process :process_original_version
def process_original_version
if model.large
resize_to_fit(800,600)
else
resize_to_fit(300,300)
end
end
end
For a specific version:
class BannerUploader < CarrierWave::Uploader::Base
include CarrierWave::MiniMagick
storage :file
def store_dir
"uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
end
version :normal do
if model.large
process resize_to_fit: [800,600]
else
process resize_to_fit: [300,300]
end
end
end

Answer 2

Ok so #Alex Kojin has the right answer. However I was faced with another problem as well. When the user submitted the form, the image would be resized always as small (300x300) because for some reason the image resize process would be executed first and then the "large" attribute would be set as true. Therefore the Uploader would always get model.large as false.
So this is how I had to change my action controller
def create
#banner=Banner.new
#banner.large=params[:large]
#banner.update_attributes(banner_params)
#banner.save
redirect_to :back
end
Not sure if this is the right approach but does work for me.