Dynamic nested form elements based on inputting a starting number

Like many others, I'm new to Rails and have a question. I'm workin开发者_开发百科g on a sample tracker for a small analytical lab. I would like users to submit batches consisting of many samples. I want the front page to be a simple gateway into batch submission. My general plan is:

1. Front page asks for number of samples in batch. User enters number and hits submit.
2. A form is generated where the user can enter batch information (Sampling date, experiment name, batch model stuff). Under the batch fields there should be as many fields for individual sample IDs as the user indicated in the first step.
3. User fills all this out and the batch and its samples are created upon submission.

My feeling is that the homepage should pass some sort of parameter to the batches controller, which then iteratively builds the samples while the model has a method to iteratively build form elements for the view. Is this thinking correct? How could I pass a parameter that isn't directly related to any models or controllers? I could find any similar questions, but if anyone can link me to a solution for a similar problem or a Railscast or something I'd be very grateful!

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There's no need to back a form with a model. For your view, you'll just want something like this example (in Haml):

- form_tag new_batch_path, :method => "get" do
  = label_tag(:sample_count, "Number of samples:")
  = text_field_tag(:sample_count, 3)
  = submit_tag("Get Started!")

And then in your controller, and the new_batch view, you can just reference params[:sample_count]

- (params[:sample_count] || 5).to_i.times do |n| ...

Because this isn't tied to a model (and nothing's being saved anyway) you can't use model validations to check the value. If you do want to verify, you'll do the verification in the batches controller - either as a before_filter, or just inline:

@sample_count = params[:sample_count].to_i
unless (1..10).include? @sample_count
  flash[:error] = "A batch must contain between 1 and 10 samples."
  redirect_to root_url
end

Note that nil.to_i, "".to_i and rubbish like "ajsdgsd".to_i all equal 0, so unless you want people to be able to specify 0 samples, this code is fairly robust

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Have a look at these Railscasts series:

• Nested Model Form: Part 1, Part 2
• Complex Forms: Part 1, Part 2, Part 3

The "Nested Model Form" screencasts are newer, so I'd go with these ones first.