Laravel Polymorphic Follows System.

create_follows_table.php

<?php

declare(strict_types=1);

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

return new class extends Migration
{
    public function up(): void
    {
        Schema::create('follows', function (Blueprint $table) {
            $table->id();
            $table->foreignId('user_id')->constrained()->onDelete('cascade');
            $table->morphs('followable');
            $table->unique(['user_id', 'followable_id', 'followable_type']);
            $table->timestamps();
        });
    }
    
};

HandleFollows.php

<?php

declare(strict_types=1);

// For code organisation, goes on the user model.

namespace App\Concerns;

use App\Models\Follow;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\HasMany;

trait HandleFollows
{
    public function followers(): HasMany
    {
        return $this->hasMany(Follow::class, 'followable_id', 'id')
            ->where('follows.followable_type', $this->getMorphClass());
    }

    public function following(): HasMany
    {
        return $this->hasMany(Follow::class, 'user_id', 'id');
    }

    public function isFollowing(Model $model): bool
    {
        if ($this->id === $model->id) {
            return false;
        }

        return $this->following()
            ->where('follows.followable_type', $model->getMorphClass())
            ->where('follows.followable_id', $model->id)
            ->exists();
    }

    public function isFollowedBy(Model $model): bool
    {
        return $this->followers()->where('user_id', $model->id)->exists();
    }

    public function follow(Model $model): ?Model
    {
        if (! $this->isFollowing($model)) {
            return Follow::create([
                'user_id' => $this->id,
                'followable_id' => $model->id,
                'followable_type' => $model->getMorphClass(),
            ]);
        }

        return null;
    }

    public function unFollow(Model $model): int
    {
        return $this->following()
            ->where('followable_id', $model->id)
            ->where('followable_type', $model->getMorphClass())
            ->delete();
    }
}

HasFollowers.php

<?php

declare(strict_types=1);

// Goes on the models we want the user to allow to follow (Posts, Tags, etc...)

namespace App\Traits;

use App\Models\Follow;
use App\Models\User;
use Illuminate\Database\Eloquent\Relations\MorphMany;

trait HasFollowers
{

    public function followers(): MorphMany
    {
        return $this->morphMany(Follow::class, 'followable');
    }

    public function isFollowedBy(User $user): bool
    {
        return $this->followers()->where('user_id', $user->id)->exists();
    }
}