Question

Delving into Rails’ upload functionality and actually following this railsguide.

I use the following code for the upload form:

<%= form_tag({ action: :upload }, multipart: true) do %>
    <%= file_field_tag :picture %>
    <%= submit_tag %>
<% end %>

And this is my upload method:

def upload
    uploaded_io = params[:customer][:picture]     #erroneous line!!
    File.open(Rails.root.join('public', 'uploads', uploaded_io.original_filename), 'w') do |file|
      file.write(uploaded_io.read)
    end
    flash[:notice] = "File uploaded successfully!"
    redirect_to root_path
end

I have marked the line which I believe is erroneous in the second code snippet. The upload method is just pasted from the railsguide and I adjusted the params array to [:customer].

When uploading a file I get this error:

undefined method `[]' for nil:NilClass

It refers to the line I marked above.

I also found this other question, but I haven’t figured out yet how that might help me.

What am I doing wrong? Is my form wrong or my controller method? Any help appreciated.

Answer 1

Try changing to

params[:picture]

Can always look at the logs to see how the request parameters hash is structured. When you use a form_for in rails, let’s say on a customer object like below. You then get the fields as

[:customer][:field_name] 

But since you just used the form_tag helper, it’s not encased in another hash:

<%= form_for @customer do |f| %>
 <%= f.text_field :field_name %>
<% end %>