public static string ImportProcedures(PetClinicContext context, string xmlString)
        {
            var xmlSerializer = new XmlSerializer(typeof(ProcedureImportDto[]), new XmlRootAttribute("Procedures"));
            var procedureDtos = (ProcedureImportDto[])xmlSerializer.Deserialize(new StringReader(xmlString));

            var animals = context.Animals.ToHashSet();
            var animalAids = context.AnimalAids.ToHashSet();
            var vets = context.Vets.ToHashSet();
            var proceduresList = new List<Procedure>();
            var result = new StringBuilder();

            foreach (var dto in procedureDtos)
            {
                if (IsValid(dto) == false)
                {
                    result.AppendLine("Error: Invalid data.");
                    continue;
                }

                try
                {
                    var procedure = new Procedure
                    {
                        Animal = animals.First(a => a.PassportSerialNumber == dto.AnimalSerialNumber),
                        Vet = vets.First(v => v.Name == dto.VetName),
                        DateTime = DateTime.ParseExact(dto.DateTime, "dd-MM-yyyy", CultureInfo.InvariantCulture)
                    };

                    foreach (var item in dto.AnimalAidNames)
                    {
                        var animalAidId = animalAids.First(a => a.Name == item.Name).Id;
                        if (procedure.ProcedureAnimalAids.Any(paa => paa.AnimalAidId == animalAidId))
                        {
                            throw new Exception();
                        }
                        procedure.ProcedureAnimalAids.Add(new ProcedureAnimalAid { AnimalAidId = animalAidId });
                    }

                    proceduresList.Add(procedure);
                    result.AppendLine($"Record successfully imported.");
                }
                catch (Exception)
                {
                    result.AppendLine("Error: Invalid data.");
                    continue;
                }
            }

            context.Procedures.AddRange(proceduresList);
            context.SaveChanges();

            return result.ToString().Trim();
        }