Complex template logic with {% record %} and {% with %}

egj actionkit

ActionKit's {% record %} tag can be used to build pretty complex logic directly in your page & email code.

Here's a basic example of the pattern:

{% with "[ ]"|load_json as my_variable %}
  {% if user.custom_fields.favorite_color == "purple" %}
    {% record "purple" in my_variable %}
  {% elif user.custom_fields.favorite_color %}
    {% record "not_purple" in my_variable
  {% endif %}

  {% if my_variable|length == 0 %}
    What's your favorite color?  You haven't told me yet.
  {% else %}
    It looks like your favorite color is {{ my_variable|nth:0 }}.
  {% endif %}
{% endwith %}

The trick is to wrap your whole code block in one or more {% with "[ ]|load_json" as my_variable %} statements. This lets you create arbitrary temporary variables that you can then stash computed data or state in, using {% record %}.

This can be very useful when you're dealing with loops combined with complex conditional logic. For example, we can use it to send emails about a filtered list of events, or events from multiple categories, without needing merge queries:

{% with "[]"|load_json as matching_events %}
{% for campaign_name in "first_campaign second_campaign third_campaign"|split %}
{% withevents with user as nearby_user 'campaign_name' as campaign 20 as radius 10 as limit %}
{% for event in events %}
{% if event.custom_fields.categories|force_list|contains:"parade" %}
{% record event in matching_events %}
{% endif %}
{% endfor %}
{% endwithevents %}
{% endfor %}

{% if matching_events|length == 0 %}
{% requires_value no_matching_events_found %}
{% endif %}

<ul>
  {% for event in matching_events|dictsort:"starts_at"|slice:":5" %}
  <li>{{ event.title }}
  {% endfor %}
</ul>
{% endwith %}

By stashing matching events in a temporary list instead of printing them out right away, we're able to do at least three things that would otherwise be impossible with pure backend template logic:

Checking whether we have any matching events by the end of our loop, and suppressing the email altogether (or displaying some conditional content) if no matching events were found
Re-sorting our matching events once we have the final list, even across multiple campaigns
Displaying at most five matching events, regardless of how many were found to match

One thing to be careful about is that {% record %} only seems to work with simple predefined variables. If you try to chain filters in a {% record %} statement you end up doing nothing. So instead of

{% record user.custom_fields.age|add:"1" in my_variable %}

you'll need to use a {% with %} statement to set a temporary variable:

{% with user.custom_fields.age|add:"1" as computed %}
  {% record computed in my_variable %}
{% endwith %}

The Third Bear

Just Right.

Complex template logic with {% record %} and {% with %}

egj actionkit