What's the best practice for creating computed (dynamic/virtual) attributes on entries?

Question

What is the best practice for defining an attribute on an Entry that isn't persistent? For example, I want to create a formatted string from two separate values stored in fields on the entry, but don't need to store the computed value in a field or in the database.

I realize I can do this in a template variable like so:

{% set fullName = entry.firstName ~ " " ~ entry.lastName %}

... but, it would be much better if I could define this in a more global way so it can be used any time I'm dealing with an Entry within a specific Section like so:

{{ entry.fullName }}

I've read about custom Modules but that seems like overkill. Also, Craft may not offer any API to do something like this, but Yii might?

Halp.

Answer 1

You can use behaviors to add new methods to system components. See the link above for documentation. A behavior is a class that extends yii\base\Behavior and is attached to a component using the EVENT_DEFINE_BEHAVIORS event.

First you define the class that provides your custom method:

use yii\base\Behavior;

class FullNameBehavior extends Behavior {
    public function fullName() {
        return "{$this->owner->firstName} {$this->owner->lastName}";
    }
}

The attach that behavior to the Entry class:

use craft\elements\Entry;
use craft\events\DefineBehaviorsEvent;
use yii\base\Event;

// init() method in a module
Event::on(
    Entry::class,
    Entry::EVENT_DEFINE_BEHAVIORS,
    function (DefineBehaviorsEvent $e) {
        $e->sender->attachBehaviors([
            FullNameBehavior::class,
        ]);
    }
);

Now you can use the method in Twig:

{{ entry.fullName }}

You can put the behavior class and the event hook in a module.

Alternative approaches

I don't really like behaviors in general, as it's very hard to find out where their methods are defined if you don't know about them. Also, tacking endless additional methods onto a class that doesn't really have anything to do with them is kind of bad design.

Instead, consider the following solutions:

• Use a macro or a Twig filter or function to display the full name consistently.
• Install the Preparse Field plugin and store the full name in a preparse field.
• If feasible, you could represent people as Users instead of Entries – they come with a computed fullName property by default.