_form.html.erb

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

  <div class="field">
    <%= form.label :csv_file %>
    <%= form.file_field :csv_file %>
  </div>

  <div class="actions">
    <%= form.submit %>
  </div>
<% end %>