Link to new record with automatic belongs_to relationship?

Question

In my Rails 3 application I have a simple model relationship which is as follows:

Animal Model

has_many :claims

Claim Model

belongs_to :animal
has_many :payments

Payments Model

belongs_to :claim

The claim table has a column called animal_id and the payments table has a column called claim_id.

I can successfully list all payments owned by a claim.

What I am trying to do is add a link within the animal show view that creates a new claim with the animal_id already set and the same with the claim show view for the new payment link.

From what I have read you can manually create a link_to with the controller and action set, like so:

Claim Show View

<%= link_to 'Create a Payment', {:controller => "payments", :action => "new", :claim_id => '@claim.id'} %>

This doesn't seem to work, although it does correctly link to the new payment page.

Is there a simpler way?

Answer 1

Off the top of my head, and untested, I think the following would work:

= link_to 'Create Payment', payments_path(:payment=>{:claim_id=>@claim.id}), :method => :post

Adding a hash inside the url helper is just going to put params on the url, which will be interpreted by rails the same way "normal" params posted from a form are.

This will be equivalent to submitting a new payment form, so it will redirect the same way that would. If you want it to be handled via ajax just add :remote => true, and be sure your the create action on your PaymentsController responds to javascript correctly.

---

Update: Read your question again, you want the new payment form with the claim_id already set?

Ok, there are many ways you could do this. If you pass params to the new action you can take the claim_id from the params, the same as I showed above for creating a record:

= link_to 'New Payment', new_payment_path(:claim_id=>@claim.id)

This should link you to /payments/new?claim_id=123

Then in your controller:

def new
  @payment = Payment.new(:claim_id => params[:claim_id])
end

However, as was pointed out in the comments, the better way to do this is to nest payments under claims:

In your routes:

resources :claims do
  resources :payments
end

In your PaymentsController:

before_filter :load_claim

def new
  @payment = @claim.payments.build
end

def create
  @payment = @claim.payments.build(params[:payment])
  ...
end

private
def load_claim
  @claim = Claim.find(params[:claim_id])
end

In your link:

= link_to 'New Payment', new_claim_payment_path(@claim)

Just be aware that now your payment path helpers will need claims in them, ie:

= link_to 'Payment', claim_payment_path(@claim, payment)

Same thing for form helpers:

= form_for [@claim, @payment] ...