Phoenix crashing after embedding `case` in template

Phoenix Forum Questions / Help
, ,
1

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
2

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.

3

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?

4

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
5

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.

6

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