hasOne(DepartmentLeadership::class)->whereNull('ended_at'); } public function announcements(): HasMany { return $this->hasMany(Announcement::class); } public function courses(): HasMany { return $this->hasMany(Course::class); } public function leaderships(): HasMany { return $this->hasMany(DepartmentLeadership::class); } public function students(): HasMany { return $this->hasMany(Student::class); } public function lecturers(): BelongsToMany { return $this->belongsToMany(Lecturer::class, 'lecturer_department'); } }