ASP.NET Core Web API中TryGetValue空键参数异常问题

开发ASP.NET Core Web API后端，调用外部API获取数据后，在AssignName()方法中调用Dictionary.TryGetValue时触发异常，错误信息为「Value cannot be null. (Parameter 'key')」。经排查，异常是由于传入TryGetValue的key（delivery.StatusId或delivery.CustomerId）为null导致。

相关代码 #

public async Task<IPagedList<TblDeliveryModel>> Handle(GetListTblDeliveryQuery request, CancellationToken cancellationToken)
{
     if (request == null)
     {
         throw new BaseException("Bạn chưa nhập dữ liệu gì");
     }

     var query = from p in _repository.Table<TblDelivery>()
                 select p;

     // API Customer
     var uriCustomer = _configuration["Api:Pos"]+ "/api/v1/TblDmCustomer/get-customer-by-list-id?ids=201777&ids=201778&ids=201779&ids=201780";
     MessageResponse response = await _callApiService.CallAPIAsync<MessageResponse>(uri: uriCustomer, bearerToken: _authorizeExtension.AcessToken);

     List<DeliveryCustomerModel> listCutomers = response.data.ToObject<List<DeliveryCustomerModel>>();
     
     if (!string.IsNullOrEmpty(request.KeySearch)) // KeySearch Có ký tự nhập vào thì
     {
         if (long.TryParse(request.KeySearch, out var _IdCus))
         {
             query = from p in _repository.Table<TblDelivery>()
                     where p.OrderHeaderId == _IdCus
                     select p;
         }
         else
         {
             throw new BaseException("KeySearch tìm kiếm theo OrderHeaderId, không được nhập chuỗi ký tự");
         }
     }

     // Call API
     var uri = Url.Mdm_Url + "TblDmDeliveryStatus/get-all";
     MessageResponse responseStatus = await _callApiService.CallAPIAsync<MessageResponse>(uri: uri, bearerToken: _authorizeExtension.AcessToken);

     List<DeliveryStatusModel> listDeliveryStatusModel = responseStatus.data.ToObject<List<DeliveryStatusModel>>();

     // order
     var orderDelivery = query.OrderByDescending(c => c.CreateDate);

     if (!string.IsNullOrEmpty(request.Sort))
     {
         var fieldType = request.Sort.GetPropertyGetter<TblDelivery>();
         orderDelivery = request.IsOrder == true ? query.OrderBy(fieldType) : query.OrderByDescending(fieldType);
     }

     // Take and skip danh sách
     var pageList = await orderDelivery.PagedList(request.Take, request.Skip);
     PagedList<TblDeliveryModel> res = new PagedList<TblDeliveryModel>();
     res.Lists = _mapper.Map<List<TblDeliveryModel>>(pageList.Lists);
     res.Count = pageList.Count;
     AssignName(res, listDeliveryStatusModel,listCutomers);

     if (!res.Lists.AnyList())
     {
         throw new BaseException("Không có dữ liệu");
     }

     return res;
}

public void AssignName(PagedList<TblDeliveryModel> tblDelvieryModel, List<DeliveryStatusModel> listDeliveryStatusModel, List<DeliveryCustomerModel> listDeliveryCustomer)
{
     var statusDictionary = listDeliveryStatusModel.ToDictionary(x => x.Id, x => x.Name);
     var customerDictionary = listDeliveryCustomer.ToDictionary(x => x.Id, x => x.Name);

     foreach (var delivery in tblDelvieryModel.Lists)
     {
         if (statusDictionary.TryGetValue(delivery.StatusId, out var statusName))
         {
             delivery.Status = statusName;
         }

         if (customerDictionary.TryGetValue(delivery.CustomerId, out var nameCustomer))
         {
             delivery.NameCustomer = nameCustomer;
         }
     }
}

异常信息 #

[External Code]
Api.App.Application.Query.Handler.Delivery.GetListTblDeliveryQueryHandler.AssignName(Hacom.Core.Infrastructure.PagedList<Api.App.Application.Query.Model.Delivery.TblDeliveryModel>, System.Collections.Generic.List<Api.App.Application.Query.Handler.Delivery.Model.DeliveryStatusModel>, System.Collections.Generic.List<Api.App.Application.Query.Handler.Delivery.Model.DeliveryCustomerModel>) in GetListTblDeliveryQuery.cs

Message: Value cannot be null. (Parameter 'key')

StackTrace: 

at System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
at System.Collections.Generic.Dictionary`2.FindValue(TKey key)    
at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value)
at Api.App.Application.Query.Handler.Delivery.GetListTblDeliveryQueryHandler.AssignName(PagedList`1 tblDelvieryModel, List`1 listDeliveryStatusModel, List`1 listDeliveryCustomer) in D:\USB_MSI\Intern_Hacom\BuildProject_Pos\_hacom\hacom\project\api\hacom.api.delivery-and-testing\Api.App\Application\Query\Handler\Delivery\GetListTblDeliveryQuery.cs:line 108

解决方案 #

方案1：调用TryGetValue前先检查key是否为null #

修改AssignName方法，在调用TryGetValue前先判断key是否为null，避免传入空值：

public void AssignName(PagedList<TblDeliveryModel> tblDelvieryModel, List<DeliveryStatusModel> listDeliveryStatusModel, List<DeliveryCustomerModel> listDeliveryCustomer)
{
     var statusDictionary = listDeliveryStatusModel.ToDictionary(x => x.Id, x => x.Name);
     var customerDictionary = listDeliveryCustomer.ToDictionary(x => x.Id, x => x.Name);

     foreach (var delivery in tblDelvieryModel.Lists)
     {
         // 检查StatusId不为null再执行查找
         if (delivery.StatusId != null && statusDictionary.TryGetValue(delivery.StatusId.Value, out var statusName))
         {
             delivery.Status = statusName;
         }

         // 检查CustomerId不为null再执行查找
         if (delivery.CustomerId != null && customerDictionary.TryGetValue(delivery.CustomerId.Value, out var nameCustomer))
         {
             delivery.NameCustomer = nameCustomer;
         }
     }
}

方案2：使用GetValueOrDefault方法（.NET Core 2.0+） #

Dictionary<TKey, TValue>.GetValueOrDefault允许传入null key且不会抛出异常，若key不存在或为null则返回类型默认值：

public void AssignName(PagedList<TblDeliveryModel> tblDelvieryModel, List<DeliveryStatusModel> listDeliveryStatusModel, List<DeliveryCustomerModel> listDeliveryCustomer)
{
     var statusDictionary = listDeliveryStatusModel.ToDictionary(x => x.Id, x => x.Name);
     var customerDictionary = listDeliveryCustomer.ToDictionary(x => x.Id, x => x.Name);

     foreach (var delivery in tblDelvieryModel.Lists)
     {
         delivery.Status = statusDictionary.GetValueOrDefault(delivery.StatusId);
         delivery.NameCustomer = customerDictionary.GetValueOrDefault(delivery.CustomerId);
     }
}

额外建议 #

• 从数据库查询TblDelivery时，若允许StatusId或CustomerId为null，需在业务逻辑中明确空值处理规则
• 外部API返回的字典源数据，需提前校验x.Id是否为null（ToDictionary会在源数据key为null时直接抛出异常）

内容的提问来源于stack exchange，提问作者Thanh DevS