Populating a preload_replace variable based on an embed conditional

Question

I like to have both thumbnail and og:image meta tags populated for the pages I build (for use by Facebook, Google and other services), and am trying to streamline my approach.

I want a generic, site-wide image to be specified when displaying a page with no specific image assets, while being able to specify a specific image when warranted (passed via an embed variable).

Here is my approach:

{embed="_global/_header" thumbnail="http://mysite.com/images/articles/some-image.jpg"}

Then in _header:

{if embed:thumbnail}{preload_replace:thumbnail="{embed:thumbnail}"}{/if}
{preload_replace:thumbnail="{site_url}/assets/img/thumbnail.jpg"}

...

<meta name="og:image" content="{thumbnail}" />
<meta name="thumbnail" content="{thumbnail}" />

This works great when I'm passing a thumbnail URL via the embed (as the first value set for a preload_replace variable is used and subsequent ones are ignored), but when I do not pass a value, {thumbnail} ends up empty (rather than using my assigned {site_url}/assets/img/thumbnail.jpg value).

Can anyone see an error in my approach here? Why would {thumbnail} be parsed within my conditional (ending up empty) when I haven't passed that embed variable?

score 3 · Accepted Answer · answered Nov 01 '12 at 16:16

The following works when I try it in EE2.5.3:

{if embed:thumbnail == ''}{preload_replace:thumb="/assets/img/thumbnail.jpg"}{/if}
{if embed:thumbnail != ''}{preload_replace:thumb="{embed:thumbnail}"}{/if}

If I reverse the order, it does not work and I get the behaviour you reported - fine if there is an embed parameter and empty otherwise.

As to exactly why this order works, I don't know - perhaps parse order related like so many EE quirks. Hopefully someone else can explain why it works and we can all learn :)

Adrian Macneil · Answer 2 · 2012-10-31T22:27:24.173

2

You might want to try writing your conditional like this, to avoid weird EE parse order issues:

{if "{embed:thumbnail}" == ""}
    {preload_replace:thumbnail="{embed:thumbnail}"}
{/if}

Also, I'm not too familiar with preload_replace, but you could solve this using Stash? It has the added advantage that you could set your thumbnail from further down in your page template (e.g. set it dynamically from your channel content).

In your page template:

{embed="_global/_header"}
{exp:stash:set name="thumbnail"}http://mysite.com/images/articles/some-image.jpg{/exp:stash:set}

In your header embed:

{!-- set the default thumbnail --}
{exp:stash:set name="thumbnail" replace="no"}http://mysite.com/images/default.jpg{/exp:stash:set}
<meta name="og:image" content='{exp:stash:get name="thumbnail"}' />
<meta name="thumbnail" content='{exp:stash:get name="thumbnail"}' />

edited Oct 31 '12 at 22:27

answered Oct 31 '12 at 21:50

Adrian Macneil

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Ah yes, another answer involving Stash! Colour me surprised, haha. Thanks for that, though since this *should* work natively, I'm looking to solve it natively. The quoted embed variable conditional made no difference unfortunately. – Derek Hogue Nov 01 '12 at 12:29
Hah, of course. It's pretty much standard in most installs now though, so doesn't add any extra overhead :) – Adrian Macneil Nov 01 '12 at 12:52

score 0 · Answer 3 · edited May 23 '17 at 12:31

I've taken the same approach as Adrian is suggesting with meta data and it would work for your thumbnails too - thought it is generally a pretty different way of thinking about your templates. I described the approach in an earlier Stack Exchange answer to a question about populating the page tags with entry data without needing multiple entries loops here.

When I use stash for meta data, I will do effectively the same thing you want to do with your thumbnail - have conditional fallback to a default value when the entry-specific data is not entered/available. I run that conditional at the entry level and then stash:set the result. Then in the meta header - which is all part of my embedded layout wrapper template - I use stash:get to retrieve the stashed result. The same thing can be done with just about any data you want to set at one point in the parse order and get later in the parse order - regardless of where it appears in wrapper template since as an embed (and commonly the only one you would use in a stash setup) it's parsed later than your entries loop logic.

Populating a preload_replace variable based on an embed conditional

3 Answers3