Phoenix crashing after embedding `case` in template

Hey,
I recently started building my first Phoenix app, it’ll be a YT downloader.

Design
So, when I started implementing searching I realised that you can search for playlist, channels and videos.
I thought about two designs:

  1. create universal thumbnail template and embed switching between types in view module.
  2. create 3 separate thumbnails and use case to get type from received API response, rendering appropriate partial template

The problem
I went with 2nd solution, but after writing it Phoenix crashes. Here’s the code:

<%= for item <- @search_results["items"] do %>
  <% case kind(item["id"]) do %>
    <% :playlist -> render "playlist_thumbnail.html", data: extract_video_data(item), conn: @conn %>
    <% :video -> render "video_thumbnail.html", data: extract_video_data(item), conn: @conn %>
  <% end %>
<% end %>

def kind(%{"kind" => "youtube#playlist"}), do: :playlist
def kind(%{"kind" => "youtube#video"}), do: :video
def kind(_), do: :error

Error:

== Compilation error in file lib/yt_downloader_web/views/search_view.ex ==
** (SyntaxError) lib/yt_downloader_web/templates/search/search.html.eex:3: syntax error before: ‘->’
(eex) lib/eex/compiler.ex:45: EEx.Compiler.generate_buffer/4
(eex) lib/eex/compiler.ex:54: EEx.Compiler.generate_buffer/4
(phoenix) lib/phoenix/template.ex:378: Phoenix.Template.compile/2
(phoenix) lib/phoenix/template.ex:186: anonymous fn/3 in Phoenix.Template.“MACRO-before_compile”/2
(elixir) lib/enum.ex:1899: Enum."-reduce/3-lists^foldl/2-0-"/3
(phoenix) expanding macro: Phoenix.Template.before_compile/1
lib/yt_downloader_web/views/search_view.ex:1: YtDownloaderWeb.SearchView (module)
(elixir) lib/kernel/parallel_compiler.ex:198: anonymous fn/4 in Kernel.ParallelCompiler.spawn_workers/6

Questions

  1. Did I missed something in case?
  2. Is there simpler or more Phoenixy way to do this?

EDIT:
I got it working by using:

<%= for item <- @search_results["items"] do %>
  <%= case kind(item["id"]) do %>
    <% :playlist -> %> <%= render "playlist_thumbnail.html", data: extract_video_data(item), conn: @conn %>
    <% :video -> %> <%= render "video_thumbnail.html", data: extract_video_data(item), conn: @conn %>
  <% end %>
<% end %>

But I still dunno why this is working and why earlier code wasn’t working. Anybody?

2 Likes

EEx - Tags:

All expressions that output something to the template must use the equals sign (=). Since everything in Elixir is an expression, there are no exceptions for this rule.

i.e. case/2 is an expression, not some kind of a switch statement.

Okey, but even with double <%= %> in case and comprehension it crashes. I didn’t go digging into macros yet, but if I understand this correctly case/2 evaluates to matching expression or nil. Doesn’t that mean I should be able to connect match -> and render call into one <% %> as this is in body of case?

You’re the one with access to the source code - tried this yet?

<%= for item <- @search_results["items"] do
      case kind(item["id"]) do
        :playlist -> 
          render "playlist_thumbnail.html", data: extract_video_data(item), conn: @conn
        :video -> 
          render "video_thumbnail.html", data: extract_video_data(item), conn: @conn 
      end
    end %>

or

<%= for item <- @search_results["items"] do %>
  <%= case kind(item["id"]) do
        :playlist -> 
          render "playlist_thumbnail.html", data: extract_video_data(item), conn: @conn
        :video -> 
          render "video_thumbnail.html", data: extract_video_data(item), conn: @conn 
      end %>
<% end %>
5 Likes

Oooh, I was convinced that I have to use <% %> per line.

Thank you so much, this is working.

Sidenote:
As a beginner I’m kinda confused in official guide, I couldn’t find anywhere guide that tell where I should put what. For instance, entire folder structure, design guide, etc. There’re bits of this knowledge shattered in docs, but some page gathering this would be very helpful.

In this case I was just extrapolating from the example:

<%= if true do %>
  It is obviously true
<% else %>
  This will never appear
<% end %>

Knowing that everything in Elixir is an expression if true evaluates to "It is obviously true". If I’m not mistaken that could be rewritten as:

<%= if true do
      "It is obviously true"
    else
      "This will never appear"
    end %>

so the separate <% %> are just there to keep the quotes around the strings out of the template.

2 Likes