why accessor method not firing?

I am following an example for how to upload a file from the great book Agile Web Development with Rails (p 541-543, to be exact); however, instead of an image file, I need to upload a csv file containing data that will get parsed and stored in the database.
I believe I am following the example almost exactly, but for some reason, my accessor method in my model that does the file parsing, is not firing?
Here’s the code:
in my view:
<% form_tag (:action=> ‘create’, :multipart => true) do %>
<%= file_field_tag ‘uploaded_file’, :size=>50 %>

<%= submit_tag "Upload" %>

<% end %>
in my controller:
def create
@upload = Upload.new(params[:id])
respond_to do |format|
if @upload.save
flash[:notice] = ‘Upload was successful.’
format.html { redirect_to(@upload) }
format.xml { render :xml => @upload, :status => :created, :location => @upload }
else
format.html { render :action => “new” }
format.xml { render :xml => @upload.errors, :status => :unprocessable_entity }
end
end
end
and in my model:
def uploaded_file=(file_field)
self.filename = base_part_of(file_field.original_filename)
# is here is where the uploaded file can be parsed?
FasterCSV.foreach(file.path,:headers=>“first_row”, :col_sep=>"\t") do |row|
row.each{|row| puts “row: #{row.inspect}”}
end
end
Following the example from the book, the “magic” part is the fact that the file is uploaded in an attribute called uploaded_file, but there is no database table that contains such a column. Instead, by naming an accessor method in the model with the same name, it will receive the uploaded file.
However, when I submit a file, I just get the following error:
ActiveRecord::StatementInvalid in UploadsController#create

PGError: ERROR: null value in column "filename" violates not-null constraint

which seems to indicate that the @upload.save is firing without the accessor method having obtained the filename for it to be populated when the
upload object gets saved. But why would the book example work, and not in my case?

I would extremely grateful if anyone can point out to me the error my ways!

thanks,
rixter

I am following an example for how to upload a file from the great book Agile
Web Development with Rails (p 541-543, to be exact); however, instead of an
image file, I need to upload a csv file containing data that will get parsed
and stored in the database.

I believe I am following the example almost exactly, but for some reason, my
accessor method in my model that does the file parsing, is not firing?

Here's the code:

in my view:
<% form_tag (:action=> 'create', :multipart => true) do %>

The multipart option needs to be separate from the routing options.
(ie ({:action => 'blah'}, :multipart => true))

Fred