*/ use HasFactory; protected $fillable = ['course_id', 'title', 'order_index', 'video_id', 'duration_seconds', 'transcript']; public function course(): BelongsTo { return $this->belongsTo(Course::class); } public function concepts(): BelongsToMany { return $this->belongsToMany(Concept::class); } public function quizzes(): HasMany { return $this->hasMany(Quiz::class); } public function progressFor(int $userId): ?LessonProgress { /** @var LessonProgress|null $progress */ $progress = $this->hasOne(LessonProgress::class) ->where('user_id', $userId) ->first(); return $progress; } }