How to handle error messages in polymorphic associations for rails?

Question

I have been following a polymorphic association tutorial at this website https://www.richonrails.com/articles/polymorphic-associations-in-rails

Unfortunately, the author did not provide the second-half of the tutorial.

I wonder what is correct syntax for handling error messages.

In interactions/new.html.erb,

<%= form_form [@context, @interaction] do |f| %>
  <% render 'shared/errors', object: f.object%>

In shared/_errors.html.erb,

<% if object.errors.any? %>
  <div id="error_explanation">
    <div class="alert alert-danger">
      The form contains <%= pluralize(object.errors.count, "error") %>.
    </div>
    <ul>
     <% object.errors.full_messages.each do |msg| %>
      <li><%= msg %></li>
     <% end %>
    </ul>
 </div>
<% end %>

When a user try to enter a new interaction in error, says excess words limit, it is supposed to tell user that. However, nothing would happen.

It is easy if it is not polymorphic association, <%= form_form @interaction do |f| %> would work.

I have tried <%= form_form [@context, @interaction] do |f| %> <% render 'shared/errors', object: f.[@context, @interaction] %> It did not work.

Any clues for me? Thanks in advance! (ruby 2.3.3, rails 5.0.1)

Answer 1

Just figured this out today! May not explain this the best but the issue is that when errors happen and the form is re-rendered, the errors are saved to the object (@interaction) that you were calling save on (@interaction.save). It creates this error object ActiveModel::Errors:0x007f62d4221698. If you "logger.debug @interaction.errors.full_messages" in create method, you can see the error messages

if @interaction.save
  redirect_to context_url(context), notice: "The interaction has been successfully created."
else
  logger.debug @interaction.errors.full_messages
  render 'new'
end

When you call the form_for [@context, @interaction] with multiple variables the form builder cannot see the previous @interaction errors ActiveModel::Errors:0x007f62d4221698, I don't know the exact reason why, but the form builder seems to create a new ActiveModel::Errors which has no errors.

You just need to specified the f.object with the object @interaction that has the error object from the create method. Below you can see the solution.

  <%= form_form [@context, @interaction] do |f| %>
  <% render 'shared/errors', object: @interaction %>