HasAuxModel.php

<?php
namespace UserFrosting\Sprinkle\Site\Database\Concerns;

/**
 * Implements event and linking methods for extended models.
 *
 * Set the member variable $auxType in your derived class.
 */
trait HasAuxModel
{
    /**
     * The "booting" method of the model.
     *
     * @return void
     */
    protected static function bootHasAuxModel()
    {
        /**
         * Create a new aux model if necessary, and save the associated aux every time.
         */
        static::saved(function ($super)
        {
            // Link subtype object, creating it if it doesn't already exist
            // and setting the id from the parent model
            $super->linkAuxModel();

            // Save related child object
            if ($super->auxType) {
                $super->aux->save();
            }
        });
    }

    /**
     * Required to be able to access additional relationships in Twig without needing to do eager loading.
     * @see http://stackoverflow.com/questions/29514081/cannot-access-eloquent-attributes-on-twig/35908957#35908957
     */
    public function __isset($name)
    {
        if (in_array($name, [
            'aux'
        ])) {
            return true;
        } else {
            return parent::__isset($name);
        }
    }

    /**
     * Relationship for interacting with aux model.
     */
    public function aux()
    {
        return $this->hasOne($this->auxType, 'id');
    }

    /**
     * If this instance doesn't already have a related aux model (either in the db on in the current object), then create one
     */
    protected function linkAuxModel()
    {
        if ($this->auxType) {
            $this->createAuxModelIfNotExists();
            $this->setAuxModelPrimaryKey();
        }
    }

    /**
     * Create and attach aux subtype model if it doesn't exist.
     */
    protected function createAuxModelIfNotExists()
    {
        if (count($this->aux)) {
            return;
        }

        // Needed to immediately hydrate the relation.  It will actually get saved in the bootHasAuxModel method.
        $this->setRelation('aux', new $this->auxType);
    }

    /**
     * Copy the parent id to the aux model, if the parent has an id at this point but the aux doesn't
     */
    protected function setAuxModelPrimaryKey()
    {
        if (isset($this->id) && !isset($this->aux->id)) {
            $this->aux->id = $this->id;
        }
    }
}