Question

When I acesss http://example.com/users/1/messages/new it says

undefined method `error_message_on' for #<#<Class:0x00000005921d50>:0x0000000591e448>

If I delete the lines that have “error_message_on” from view,
no error appears but it shows blank page. so weird 🙁

messages new view is just like this. whats wrong?
Thanks in advance!!

<% form_for @message, :url => user_messages_path(@user) do |f| %>
  <p>
    To:<br />
        <%= f.text_field :to %>
        <%= error_message_on @message, :to %>
  </p>
  <p>
    Subject:<br />
    <%= f.text_field :subject %>
    <%= error_message_on @message, :subject %>
    </p>
    <p>
      Message<br />
      <%= f.text_area :body %>
            <%= error_message_on @message, :body %>
    </p>
    <p>
      <%= submit_tag "Send" %>
    </p>
<% end %>

Answer 1

You need to change the erb tags you are using for the form_for declaration. It should be <%= instead of <%. That should fix the blank page.

As far as how to display the error messages, error_message_on was deprecated in Rails 2.3.8. You’ll need to use something that is supported in your version of Rails. This question might be of use and there’s also this one