disable button if user has previously performed that action - ruby-on-rails

Question

Tried to figure this out for a while without being able to crack the nut.
What I am trying to do is this.
I have a user model, it has_many answers. I would like to restrict the ability for one user to answer the same answer more than once. I've been able to block this in the model, however not in the view.
I would like the submit button to see if the current_user.id is present in the current answer id (the one it's thinking about filling out), if so disable the submit button saying "already applied".
My answers#new
<%= form_for #answer do |f| %>
<%= f.hidden_field :application_id, value: #application.id %>
<% if #application.question_2.length && #application.question_3.length >= 1 %>
<p>Question 1: <%= #application.question_1 %></p>
<%= f.text_area :answer_1 %><br/>
<p>Question 2: <%= #application.question_2 %></p>
<%= f.text_area :answer_2 %><br/>
<p>Question 3: <%= #application.question_3 %></p>
<%= f.text_area :answer_3 %>
<% elsif #application.question_2.length >= 1 %>
<p>Question 1: <%= #application.question_1 %></p>
<%= f.text_area :answer_1 %><br/>
<p>Question 2: <%= #application.question_2 %></p>
<%= f.text_area :answer_2 %><br/>
<% else %>
<p>Question 1: <%= #application.question_1 %></p>
<%= f.text_area :answer_1 %><br/>
<% end %>
<%= f.submit "Submit answers", data: { disable_with: "Please wait..." } %>
<% end %>

Answer 1

I see a couple different pieces of this. When I write similar functionality, I think about the following questions:
What should happen on page load / reload?
Should anything happen without page reload (ie. via AJAX / JS)?
Should the action be disabled server-side, client-side, or both?
First of all, if the user has already submitted an answer by the time the page loads, the template should display the button differently. Usually it makes sense to not display a form at all in that case, but if you want the form with the button disabled, the following code comes to mind (see html example):
<% if #user_has_answered %>
<%= f.submit "Submit answers", disabled: true %>
<% else %>
<%= ... normal button ... %>
<% end %>
If you're concerned about preventing the user from clicking the button twice when they submit the form from the page, some simple Jquery can easily handle that, or you can use disable_with as in your example twice. This has nothing to do with the state of the database; it merely sets up a Javascript listener that disables the button as soon as it's clicked (and changes its text) to prevent the user from accidentally double-submitting when pages load slowly.
You mentioned that you have prevented double answers in the model. How does the controller handle this? If a user somehow manages to fill out the form a second time and submit it (perhaps Javascript is disabled and they had multiple tabs open on the same page? If it's possible, users do it), what do you want to happen to the data they've submitted? Show them a rejection message? Preserve their data on the same page? This functionality should be 80% automatic in Rails, if you want it, as long as you handle the request and rejection in the same way that form validation errors are handled.
I'm happy to be more specific if you share more detail about what you're looking for or having trouble with.

Answer 2

Assuming that Answer belongs_to Application, you could do...
<% if current_user.answers.collect(&:application).include?(#application) %>
<%= f.submit "already applied", disabled: true %>
<% else %>
<%= f.submit "Submit answers", data: { disable_with: "Please wait..." } %>
<% end %>