How do I sort a collection of entries from multiple sections by date?

Question

I want to create a featured story slider on my website and gather the latest entries from multiple channels to populate it.

Here is what is working:

# fetch the entries
{% set featuredBlog = craft.entries.section('blogs').limit(1).find() %}
{% set featuredArticle = craft.entries.section('articles').limit(1).find() %}
{% set featuredSpecialReport = craft.entries.section('specialReports').limit(1).find() %}
{% set featuredInfographic = craft.entries.section('infographics').limit(1).find() %}

# create a collection out of the above entries
{% set allEntries =
featuredBlog|merge(featuredArticle)|merge(featuredSpecialReport)|merge(featuredInfographic) %}

# loop over the collection and output them
{% for featuredEntry in allEntries %}
  {{ featuredEntry.title }}<br>
{% endfor %}

Now I want to sort the collection of entries by postDate so that the latest entry in the collection shows up first, no matter what section it is from. How do I do this?

I tried:

{% for featuredEntry in allEntries|group('postDate.day') %}
  {{ featuredEntry.title }}<br>
{% endfor %}

But this doesn't work and crashes the template saying Key "title" for array with keys "0, 1, 2" does not exist

So how do I sort a collection of entries from multiple sections and show them by latest date descending?

Answer 1

Rather than fetching the entries at first, just grab their IDs using ids() instead of find():

{% set featuredBlogId = craft.entries.section('blogs').limit(1).ids() %}
{% set featuredArticleId = craft.entries.section('articles').limit(1).ids() %}
{% set featuredSpecialReportId = craft.entries.section('specialReports').limit(1).ids() %}
{% set featuredInfographicId = craft.entries.section('infographics').limit(1).ids() %}

Then merge all of those arrays together:

{% set featuredIds = featuredBlogId
    |merge(featuredArticleId)
    |merge(featuredSpecialReportId)
    |merge(featuredInfographicId) %}

Once you’ve got that array of all the latest featured entries’ IDs, you can fetch their full entry models all at once:

{% set featuredEntries = craft.entries.id(featuredIds) %}

{% for entry in featuredEntries %}
    {{ entry.title }}<br>
{% endfor %}