Post_102.4.rb

# post request in controller

  post '/request_form' do
    @form = Form.build
    Form.validate(@form, params)

    if @form.values.map(&:error).compact.any?
      erb :request_form
    else
       #continue
    end
  end
  
# form

<form action='/request_form' method='post'>
  <p>
    <label for="first_name"><%= @form[:first_name].label %></label>
    <input type="text" name="first_name" value="<%= @form[:first_name].value %>" placeholder="first name" required >
    <span class="error"><%= @form[:first_name].error %></span>
  </p>

  <p>
    <label for="middle_name"><%= @form[:middle_name].label %></label>
    <input type="text" name="middle_name" value="<%= @form[:middle_name].value %>" placeholder="optional" >
    <span class="error"><%= @form[:middle_name].error %></span>
  </p>
  ...
</form>