CarrierWave create storage directory for versions(thumb, large, medium)

Question

I wanted to create different directories for different versions of the images. To achieve this what can be done to the "store_dir" method in Uploader rails 3.2

def store_dir
    "uploads/#{model.book.id}/resource"
end

version :large do
    process :resize_to_fill => [800, 800]
end

version :thumb do
    process :resize_to_fill => [100, 100]
end