CourseWork/app/Models/Lesson.php

<?php

namespace App\Models;

use Illuminate\Contracts\Database\Eloquent\Builder;
use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsTo;
use Illuminate\Database\Eloquent\Relations\BelongsToMany;
use Illuminate\Database\Eloquent\Relations\HasMany;

class Lesson extends Model
{
    use HasFactory;

    protected $fillable = [
        'name',
        'type',
        'description',
        'lesson_date',
        'grade_id',
        'teacher_id',
        'subject_id',
    ];

    public function grade(): BelongsTo
    {
        return $this->belongsTo(Grade::class);
    }

    public function teacher(): BelongsTo
    {
        return $this->belongsTo(Teacher::class);
    }

    public function subject(): BelongsTo
    {
        return $this->belongsTo(Subject::class);
    }

    public function students(): BelongsToMany
    {
        return $this->belongsToMany(Student::class)->withPivot('score');
    }

    public function scopeFilter(Builder $query): void
    {
        $subject_id = request('subject_id');

        $query->when($subject_id, function (Builder $query, $subject_id) {
            $query->where('subject_id', $subject_id);
        });
    }
}