public void DeleteMentor(Mentor mentor, int schoolId) { // firstly, delete mentor in catalogues List <Domain.Catalogue> catalogues = _context.Catalogues .Include(c => c.MentorCatalogues).Where(c => c.SchoolId == schoolId).ToList(); List <Domain.MentorCatalogue> deleteMentorCatalogues = catalogues .SelectMany(c => c.MentorCatalogues).Where(mc => mc.MentorId == mentor.Id).ToList(); _context.RemoveRange(deleteMentorCatalogues); _context.SaveChanges(); // secondly, delete mentor in school Domain.Mentor deleteMentor = _context.Mentors.FirstOrDefault(m => m.Id == mentor.Id); _context.Mentors.Remove(deleteMentor); _context.SaveChanges(); }