Demo.php

<?php

/**
 * You should read 👇 this great article for context.
 * https://zaengle.com/blog/using-wherehas-in-laravel-polymorphic-relations
 *
 * This is an attempt to make the WhereHas queries dynamic 
 * so you don't need to specify a new method for each new type.
 */

use App\Post;
use App\Event;
use App\Comment;
use Illuminate\Database\Eloquent\Relations\Relation;

/**
 * Basic usage
 */

$events = Event::whereEventable(Post::class, function ($query) {
    $query->wherePublished();
})->get();

/**
 * Can add another class into the mix *without* changing the the Event class 🎉
 */

$events = Event::whereEventable(Post::class, function ($query) {
    $query->wherePublished();
})->orWhere->whereEventable(Comment::class, function ($query) {
    $query->etc(...);
})->get();

/**
 * Can also use morph mapped values
 */

Relation::morphMap(['posties' => Post::class]);

$events = Event::whereEventable('posties', function ($query) {
    $query->wherePublished();
})->get();

Event.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\Relation;

class Event extends Model
{
    protected $guarded = [];

    public function scopeWhereEventable($query, $type, $callback)
    {
        $this->filterPolymorphicRelation($query, 'eventable', $type, $callback);
    }

    protected function filterPolymorphicRelation($query, $name, $type, $callback)
    {
        $class = Relation::getMorphedModel($type) ?? $type;

        $query->where("{$name}_type", '=', $type)
            ->whereIn("{$name}_id", function ($query) use ($class, $callback) {
                $model = new $class;

                $query = $model->newEloquentBuilder($query)->setModel($model);

                $callback($query);
                
                $query->select([$model->getKeyName()]);
            });
    }
}

Post.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Post extends Model
{
    protected $guarded = [];

    public function scopeWherePublished($query)
    {
        $query->where('published_at', '<=', now());
    }
}