Putting logic into a Ruby on Rails application: calculate a value for a field when creating a new row of the database

I'm fairly new to Ruby on Rails. I'm building a web app that will ask a patient a series of questions, then calculate a risk using a previously validated model. When a new patient record is created, I want the application to take the data the user entered into the other fields, and use it to calculate the value of the last field. I have the logic written out, but just don't know where to actually code it into my application.

Should it go in the model, view or controller? And how should I go about including it?

My git repo: http://ift.tt/2tnoc6o

This is my view patients/form.html.erb

<%= form_with(model: patient, local: true) do |form| %>
  <% if patient.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(patient.errors.count, "error") %> prohibited this patient from being saved:</h2>

      <ul>
      <% patient.errors.full_messages.each do |message| %>
        <li><%= message %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <div class="form-group">
    <%= form.label :"First Name" %><br>
    <%= form.text_field :firstName, class: "form-control", id: :patient_firstName %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Surname" %><br>
    <%= form.text_field :surName, class: "form-control", id: :patient_surName %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Date of Birth" %>&nbsp &nbsp 
    <%= form.date_select :dob, :start_year=>1900,:end_year=>2030, id: :patient_dob %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Gender" %>&nbsp &nbsp 
    <%= form.select :gender, ["","male", "female"], id: :patient_gender %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Which hospital are you having the opperation in?" %>&nbsp &nbsp 
    <%= form.select :hospital, ["","Beaumont", "Connelly", "St. Josephs", "Naas", "Limerick"], id: :patient_hospital %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"What date are you having the opperation on?" %>&nbsp &nbsp 
    <%= form.date_select :opDate, :start_year=>2017,:end_year=>2027, id: :patient_opDate %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"How would you rate your overall health" %><br>
    <%= form.select :q1, ["","No abnormalities", "Better than expected", "Worse  than expected", "Dementia", "Sick", "Moribund"], id: :patient_q1 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"How is your physical condition in general?" %><br>
    <%= form.select :q2, ["","I can do everything I want", "Slightly impaired, but I feel no impairments in daily activities", "Impaired, I can only take care of domestic chores", "I am completely dependent on help from others"],  id: :patient_q2 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Do you have a heart condition that impedes your physical efforts (as a result of tiredness, pain or shortness of breath)?" %><br>
    <%= form.select :q3, ["","No", "Yes, only during heavy labour", "Yes, during climbing the stairs, in the wind, stress", "Yes, daily, not at rest", "Yes, at rest and increased during any activity"], id: :patient_q3 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Have you ever experienced any feeling of pain or tightness in the chest?" %><br>
    <%= form.select :q4, ["","No", "Yes, only during heavy labour", "Yes, during climbing the stairs, in the wind, stress", "Yes, daily, not at rest", "Yes, at rest and increased during any activity"], id: :patient_q4 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Have you ever had a heart attack?" %><br>
    <%= form.select :q5, ["","No", "Yes, > 12 months ago", "Yes, > 6 and < 12 months ago", "Yes, > 3 and < 6 months ago", "Yes, < 3 months ago"], id: :patient_q5 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Have you ever had a cardiac arrest?" %><br>
    <%= form.select :q6, ["","No", "Yes, > 12 months ago", "Yes, > 6 and < 12 months ago", "Yes, > 3 and < 6 months ago", "Yes, < 3 months ago"], id: :patient_q6 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Have you ever undergone any cardiac surgery or heart catheterization?" %><br>
    <%= form.select :q7, ["","No", "Yes, > 6 months ago", "Yes, > 3 and < 6 months ago", "Yes, > 6 weeks and < 3 months ago", "Yes, < 6 weeks ago"], id: :patient_q7 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Do you ever get palpitations?" %><br>
    <%= form.select :q8, ["","No", "Yes, I have no treatment", "Yes, I am treated with medication"], id: :patient_q8 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Have you been told you have a heart murmur?" %><br>
    <%= form.select :q9, ["","No", "Yes, but no operation", "Yes, I have had an operation"], id: :patient_q9 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Do you have high blood pressure?" %><br>
    <%= form.select :q10, ["","No", "I don't know", "Yes"], id: :patient_q10 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Do you have high cholesterol?" %><br>
    <%= form.select :q11, ["","No", "Yes"], id: :patient_q11 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Do you receive treatment for diabetes (high blood sugar level)?" %><br>
    <%= form.select :q12, ["","No", "Yes, treatment with diet", "Yes, treatment with oral medication", "Yes, treatment with insulin"], id: :patient_q12 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Have you ever had a stroke?" %><br>
    <%= form.select :q13, ["","No", "Yes, but complete recovery", "Yes, with physical impairment/ disability", "Yes, < 2 months ago"], id: :patient_q13 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Do you receive treatment for asthma?" %><br>
    <%= form.select :q14, ["","No", "Yes, sometimes", "Yes, often", "Yes, daily", "Yes, daily and increased over the last six months"], id: :patient_q14 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Do you receive treatment for pulmonary emphysema, chronic obstructive pulmonary disease (COPD) or chronic bronchitis?" %><br>
    <%= form.select :q15, ["","No", "Yes, only during heavy labour", "Yes, always during climbing the stairs, in the wind, stress", "Yes, always even at rest, I need oxygen therapy"], id: :patient_q15 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Do you have Sleep Apnoea?" %><br>
    <%= form.select :q16, ["","No", "Yes"], id: :patient_q16 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Do you have any renal problems or kidney impairment?" %><br>
    <%= form.select :q17, ["","No", "Yes, but with complete recovery", "Yes, treatment with fluid restriction only", "Yes, treatment with dialysis", "Yes, other serious kidney condition (e.g. kidney resection)"], id: :patient_q17 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Have you ever had jaundice or any liver problems?" %><br>
    <%= form.select :q18, ["","No", "Yes, but with complete recovery", "Yes, liver cirrhosis has been diagnosed", "Yes, other serious liver condition (e.g. partial resection)"], id: :patient_q18 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Have you ever unintentionally lost more than 10 kg in a short period of time?" %><br>
    <%= form.select :q19, ["","No", "Yes", "Yes, more than 25% of previous bodyweight"], id: :patient_q19 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Do you smoke?" %><br>
    <%= form.select :q20, ["","No", "Yes"], id: :patient_q20 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Do you consume alcohol?" %><br>
    <%= form.select :q21, ["","No", "Yes, < 3 Units/day", "Yes, > 3 and < 6 Units/day", "Yes, > 6 Units/day"], id: :patient_q21 %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.label :"Do you ever take illicit drugs (Cocaine, Heroin, Ecstasy)?" %><br>
    <%= form.select :q22, ["","No", "No, not anymore", "Yes, every once in a while", "Yes, more the once a week"], id: :patient_q22 %>
  </div>
  <hr>





  <div class="form-group">
    <%= form.label :"ASA grade" %><br>
    <%= form.select :asa, ["","1", "2", "3", "4", "5"], id: :patient_asa %>
  </div>
  <hr>

  <div class="form-group">
    <%= form.submit "Submit for Assessment", class: "btn btn-primary" %>
  </div>
<% end %>

And this is my patient controller

class PatientsController < ApplicationController
  before_action :set_patient, only: [:show, :edit, :update, :destroy]

  # GET /patients
  # GET /patients.json
  def index
    @patients = Patient.all
  end

  # GET /patients/1
  # GET /patients/1.json
  def show
    
  end

  # GET /patients/new
  def new
    @patient = Patient.new
  end

  # GET /patients/1/edit
  def edit
  end

  # POST /patients
  # POST /patients.json
  def create
    @patient = Patient.new(patient_params)
    respond_to do |format|
      if @patient.save
        format.html { redirect_to @patient }
        format.json { render :show, status: :created, location: @patient }
      else
        format.html { render :new }
        format.json { render json: @patient.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /patients/1
  # PATCH/PUT /patients/1.json
  def update
    respond_to do |format|
      if @patient.update(patient_params)
        format.html { redirect_to @patient, notice: 'Patient was successfully updated.' }
        format.json { render :show, status: :ok, location: @patient }
      else
        format.html { render :edit }
        format.json { render json: @patient.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /patients/1
  # DELETE /patients/1.json
  def destroy
    @patient.destroy
    respond_to do |format|
      format.html { redirect_to patients_url, notice: 'Patient was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_patient
      @patient = Patient.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def patient_params
      params.require(:patient).permit(:firstName, :surName, :dob, :gender, :hospital, :opDate, :q1, :q2, :q3, :q4, :q5, :q6, :q7, :q8, :q9, :q10, :q11, :q12, :q13, :q14, :q15, :q16, :q17, :q18, :q19, :q20, :q21, :q22, :asa)
    end
end

Thank you!