math_cms/app/Models/KnowledgePoint.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class KnowledgePoint extends Model
{
    use HasFactory;

    protected $fillable = [
        'name',
        'description',
        'code',
        'subject',
        'grade',
        'difficulty_level',
    ];

    protected $casts = [
        'difficulty_level' => 'integer',
    ];

    public function skills()
    {
        return $this->belongsToMany(Skill::class, 'knowledge_point_skill');
    }
}