A fieldtype that parses Twig when an element is saved, and saves the result as plain text.
All in the name of performance.

Special thanks to Mats Mikkel and Bob for invaluable help on Slack when I first built the plugin, and Carl for massively refactoring and improving the whole thing (v0.3.0). :)

1. Download the zip from this repository, unzip, and put the preparsefield folder in your Craft plugin folder.
2. Enable the plugin in Craft (Settings > Plugins)

The Preparse fieldtype is now available when you create a new field.

When creating a new Preparse field, you can add the Twig that you want to run to the fields settings. When the entry is saved, the element that is saved will be passed to the code, with the same name as it's element type (in lower case). So, if the field is attached to an entry, entry will be available. If it is attached to a category, user or global set, category, user and globalset will be available. If attached to Commerce elements, it's commerce_product, commerce_variant or commerce_order.

Usage in Matrix
When a Preparse field is added to a Matrix block, that block will be available to the Twig code as the variable matrixblock. The element (entry, category, global set etc) the Matrix field belongs to will be available under matrixblock.owner.

If you have a category field in your entry named entryCategory, you can save the category title to the preparse field by adding the following Twig to the field settings:

{{ entry.entryCategory | length ? entry.entryCategory.first().title }}

This is useful for saving preparsed values to a field for use with sorting, searching or similar things.

You can also do more advanced stuff, for instance for performance optimizing. Let's say you have three different asset fields that may or may not be populated. having to check these in the template may require a bunch of queries since you can't check if a field has a relation in Craft, without actually querying for it. You could do something like this to get the id of the asset to use:

{% if entry.smallListImage | length %}
    {{ entry.smallListImage.first().id }}
{% elseif entry.largeListImage | length %}
    {{ entry.largeListImage.first().id }}
{% elseif entry.mainImage | length %}
    {{ entry.mainImage.first().id }}
{% endif  %}

You'd probably want to wrap that in {% spaceless %} ... {% endspaceless %} to make it a bit more useful.

Or you could just use it to do some bulk work when saving, like pregenerating a bunch of image transforms with Imager (shameless plug, I know):

{% if entry.image | length %}
    {% set transformedImages = craft.imager.transformImage(entry.image.first(), [
	    { width: 1000 }, 
	    { width: 900 }, 
	    { width: 800 }, 
	    { width: 700 }, 
	    { width: 600 }, 
	    { width: 500 }, 
	    { width: 400 }, 
	    { width: 300 }, 
	    { width: 200 },
	    { width: 100 }
    ]) %}
{% endif %}

The template path is set to your site template path, so you can even include whole templates if you want to do more advanced stuff and/or want to keep your fields Twig in version control:

{% include '_fields/myFieldInclude' %}

Make sure that you always write solid Twig, taking into account that fields may not be populated yet. If an error occurs in your Twig, the element will not be saved.

The preparse field is only updated when an element is saved. If you grab data from a related element (like in the category title example above), and then update the related element, the preparsed value will not automatically be updated.

The preparse field is made to work with localized sites, but there is one gotcha. It is important that the fields that you process, and the preparse field itself, has the same locales setup. If the target field is set up to be localized to two different languages, and your preparse field is not, the value will be updated to the target field value in the language that was saved last. If your target field is not localized, but you localize your preparse field, you will need to save the entry in both languages if you change the target field.

The plugin is released under the MIT license, meaning you can do what ever you want with it as long as you don't blame me. It's free, which means there is absolutely no support included, but you might get it anyway. Just post an issue here on github if you have one, and I'll see what I can do. :)

See releases.json.