How to debug eex template and @ variables?

Question

I have this template

  <%= form_for @changeset, bid_path(@conn, :update, 1), [method: :put], fn f -> %>
    <% 
      require IEx
      IEx.pry
    %>
<%= if @changeset.action do %>
  <div class="alert alert-danger">
    <p>Oops, something went wrong! Please check the errors below.</p>
  </div>
<% end %>

How can I display @changeset in IEx console? When I'm trying to do this is blows an error:

pry(5)> @changeset
** (ArgumentError) cannot invoke @/1 outside module
    (elixir) lib/kernel.ex:3960: Kernel.assert_module_scope/3
    (elixir) expanding macro: Kernel.@/1
             web/templates/bid/edit.html.eex:5: (file)

Dogbert Dogbert · Accepted Answer · 2016-09-08T12:33:34

@ in eex templates in Phoenix is completely unrelated to @ in Elixir/iex. In eex templates in Phoenix, @foo is roughly equivalent to Access.fetch!(assigns, :foo), while in Elixir/iex, they're used to define module attributes. So, in order to access @changeset in iex, you can can do:

Access.fetch!(assigns, :changeset)

or just the following if you're okay with getting nil for non-existent keys:

assigns[:changeset]

How to debug eex template and @ variables?

2 Answers