Form with model so that we can validate (hypothetically)

app/controllers/case_logs_controller.rb

@@ -22,10 +22,11 @@ class CaseLogsController < ApplicationController
 
   def next_page
     form = Form.new(2021, 2022)
-    @case_log = CaseLog.find(params[:case_log_id])
-    previous_page = params[:previous_page]
+    @case_log = CaseLog.find(params[:id])
+    previous_page = params[:case_log][:previous_page]
     questions_for_page = form.questions_for_page(previous_page).keys
     answers_for_page = page_params(questions_for_page).select { |k, _v| questions_for_page.include?(k) }
+    begin
       @case_log.update!(answers_for_page)
       next_page = form.next_page(previous_page)
       redirect_path = if next_page == :check_answers
@@ -36,6 +37,10 @@ class CaseLogsController < ApplicationController
                       end
 
       redirect_to(send(redirect_path, @case_log))
+    rescue ActiveRecord::RecordInvalid
+      page_info = form.all_pages[previous_page]
+      render "form/page", locals: { form: form, page_key: previous_page, page_info: page_info }
+    end
   end
 
   def check_answers
@@ -51,13 +56,13 @@ class CaseLogsController < ApplicationController
   form.all_pages.map do |page_key, page_info|
     define_method(page_key) do
       @case_log = CaseLog.find(params[:case_log_id])
-      render "form/page", locals: { case_log_id: @case_log.id, form: form, page_key: page_key, page_info: page_info }
+      render "form/page", locals: { form: form, page_key: page_key, page_info: page_info }
     end
   end
 
 private
 
   def page_params(questions_for_page)
-    params.permit(questions_for_page)
+    params.require(:case_log).permit(questions_for_page)
   end
 end

app/helpers/conditional_questions_helper.rb

@@ -6,10 +6,6 @@ module ConditionalQuestionsHelper
   end
 
   def display_question_key_div(page_info, question_key)
-    if conditional_questions_for_page(page_info).include?(question_key)
-      "<div id=#{question_key}_div style='display:none;'>".html_safe
-    else
-      "<div id=#{question_key}_div>".html_safe
-    end
+    "style='display:none;'" if conditional_questions_for_page(page_info).include?(question_key)
   end
 end

app/models/case_log.rb

@@ -1,3 +1,5 @@
 class CaseLog < ApplicationRecord
   enum status: { "in progress" => 0, "submitted" => 1 }
+
+  validates :tenant_age, presence: true
 end

app/views/form/page.html.erb

@@ -1,26 +1,23 @@
 <% previous_page = form.previous_page(page_key) %>
 <% content_for :before_content do %>
-  <%= govuk_back_link href: "/case_logs/#{case_log_id}/#{previous_page}" do %>
+  <%= govuk_back_link href: "/case_logs/#{@case_log.id}/#{previous_page}" do %>
     Back
   <% end %>
 <% end %>
 
-<%= turbo_frame_tag "case_log_form", target: "_top" do %>
   <% if page_info["header"].present? %>
     <h1 class="govuk-heading-xl">
       <%= page_info["header"] %>
     </h1>
   <% end %>
-  <%= form_with action: '/case_logs', method: "next_page", builder: GOVUKDesignSystemFormBuilder::FormBuilder do |f| %>
-
+  <%= form_with model: @case_log, method: "next_page", builder: GOVUKDesignSystemFormBuilder::FormBuilder do |f| %>
+    <%= f.govuk_error_summary %>
     <% page_info["questions"].map do |question_key, question| %>
-      <%= display_question_key_div(page_info, question_key)%>
+      <div id=<%= question_key + "_div" %><%= display_question_key_div(page_info, question_key) %> >
         <%= render partial: "form/#{question["type"]}_question", locals: { question_key: question_key, question: question, f: f } %>
       </div>
     <% end %>
 
     <%= f.hidden_field :previous_page, value: page_key %>
-    <%= f.hidden_field :case_log_id, value: case_log_id %>
     <%= f.govuk_submit "Save and continue"  %>
   <% end %>
-<% end %>

config/routes.rb

@@ -3,11 +3,12 @@ Rails.application.routes.draw do
   get "about", to: "about#index"
   get "/", to: "test#index"
 
+  post '/case_logs/:id', to: "case_logs#next_page"
+
   form = Form.new(2021, 2022)
   resources :case_logs do
     form.all_pages.keys.map do |page|
       get page.to_s, to: "case_logs##{page}"
-      post page.to_s, to: "case_logs#next_page"
       form.all_subsections.keys.map do |subsection|
         get "#{subsection}/check_answers", to: "case_logs#check_answers"
       end