public string TaoPhieuThu(PhieuThu phieuthu)
 {
     if (ModelState.IsValid)
     {
         ThuChiobj.PhieuThus.Add(phieuthu);
         ThuChiobj.SaveChanges();
         return "Thanh cong";
     }
     return "Khong thanh cong";
 }
 public string SuaPhieuThu(PhieuThu phieuthu, string MaPhieuThu)
 {
     PhieuThu pt = ThuChiobj.PhieuThus.Find(MaPhieuThu);
     if (ModelState.IsValid)
     {
         pt.ThoiGianThu = phieuthu.ThoiGianThu;
         pt.LoaiPhieu_id = phieuthu.LoaiPhieu_id;
         pt.NguoiTaoPhieuId = phieuthu.NguoiTaoPhieuId;
         pt.GiaTri = phieuthu.GiaTri;
         pt.GhiChu = phieuthu.GhiChu;
         ThuChiobj.Entry(pt).State = EntityState.Modified;
         ThuChiobj.SaveChanges();
         return "A";
     }
     else
     {
         return "B";
     }
     return "C";
 }