一 配景
本日在利用EntityFrameworkCore 查询的时候在调试的时候老是提示如下错误：Unable to cast object of type 'System.Data.SqlTypes.SqlString' to type 'System.Data.SqlTypes.SqlGuid' 第一次看这个报错必定是数据库实体和EFCore中界说的某种范例不匹配从而导致范例转换错误，可是业务涉及到这么多的实体Entity,那么到底是那边范例无法匹配呢？所以第一步必定是调试代码，然后看报错信息，这里我们首先贴出完整的报错信息，从而利便本身阐明详细问题。
System.InvalidCastException: Unable to cast object of type 'System.Data.SqlTypes.SqlString' to type 'System.Data.SqlTypes.SqlGuid'. at System.Data.SqlClient.SqlBuffer.get_SqlGuid() at System.Data.SqlClient.SqlDataReader.GetGuid(Int32 i) at lambda_method(Closure , DbDataReader ) at Microsoft.EntityFrameworkCore.Storage.Internal.TypedRelationalValueBufferFactory.Create(DbDataReader dataReader) at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable`1.Enumerator.BufferlessMoveNext(DbContext _, Boolean buffer) at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerExecutionStrategy.Execute[TState,TResult](TState state, Func`3 operation, Func`3 verifySucceeded) at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable`1.Enumerator.MoveNext() at Microsoft.EntityFrameworkCore.Query.Internal.LinqOperatorProvider._TrackEntities[TOut,TIn](IEnumerable`1 results, QueryContext queryContext, IList`1 entityTrackingInfos, IList`1 entityAccessors)+MoveNext() at Microsoft.EntityFrameworkCore.Query.Internal.LinqOperatorProvider.ExceptionInterceptor`1.EnumeratorExceptionInterceptor.MoveNext() at System.Linq.Lookup`2.CreateForJoin(IEnumerable`1 source, Func`2 keySelector, IEqualityComparer`1 comparer) at System.Linq.Enumerable.JoinIterator[TOuter,TInner,TKey,TResult](IEnumerable`1 outer, IEnumerable`1 inner, Func`2 outerKeySelector, Func`2 innerKeySelector, Func`3 resultSelector, IEqualityComparer`1 comparer)+MoveNext() at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer) at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector) at Sunlight.Dcs.Application.Sales.SalesOrder.DegradedVehicleContracts.DegradedVehicleContractService.QueryByIdAsync(Int32 id) in E:\63318\sales-service\src\sales.orders\Application.Sales.Orders\SalesOrder\DegradedVehicleContracts\DegradedVehicleContractService.cs:line 99 at Abp.Threading.InternalAsyncHelper.AwaitTaskWithPostActionAndFinallyAndGetResult[T](Task`1 actualReturnValue, Func`1 postAction, Action`1 finalAction) at Sunlight.Dcs.WebApi.Sales.Controllers.Orders.DegradedVehicleContractController.QueryById(Int32 id) in E:\63318\sales-service\src\WebApi.Sales\Controllers\Orders\DegradedVehicleContractController.cs:line 50 at Microsoft.AspNetCore.Mvc.Internal.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments) at System.Threading.Tasks.ValueTask`1.get_Result() at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.InvokeActionMethodAsync() at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.InvokeNextActionFilterAsync() at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Rethrow(ActionExecutedContext context) at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.InvokeInnerFilterAsync() at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeNextExceptionFilterAsync()
二 办理方案有了上面的报错信息我们就可以或许知道大抵偏向，接下来我们首先来看看报错信息的这段代码。
public async Task<SimpleDegradedVehicleContractOutput> QueryByIdAsync(int id) { var queryResult = await _degradedVehicleContractRepository.GetAll() .Include(d => d.DegradedVehicleContractDetails) .SingleOrDefaultAsync(mp => mp.Id == id); if (queryResult == null) throw new ValidationException($"当前Id为:{id}的降级车条约没有找到"); var result = _objectMapper.Map<SimpleDegradedVehicleContractOutput>(queryResult); result.Details = _objectMapper.Map<List<DegradedVehicleContractDetailDto>>(queryResult.DegradedVehicleContractDetails); //获取ProductId var productIds = queryResult.DegradedVehicleContractDetails.Select(d => d.ProductId).Distinct().ToArray(); //车辆Id var vinLists = queryResult.DegradedVehicleContractDetails.Select(r => r.Vin).Distinct().ToArray(); var detailResult = (from detail in queryResult.DegradedVehicleContractDetails join product in _productRepository.GetAll().Where(p => productIds.Contains(p.Id)) on detail.ProductId equals product.Id join vehicleDict in _vehicleInformationRepository.GetAll().Where(v => vinLists.Contains(v.Vin)) on detail.Vin equals vehicleDict.Vin select new { ProductId = product.Id, product.ProductType, VehicleId = vehicleDict.Id, detail.Vin }).ToDictionary(r => Tuple.Create(r.ProductId, r.Vin), r => new { r.ProductType, r.VehicleId }); result.Details.ForEach(r => { r.ProductType = detailResult[Tuple.Create(r.ProductId, r.Vin)]?.ProductType; r.VehicleId = detailResult[Tuple.Create(r.ProductId, r.Vin)].VehicleId; }); return result; }
2.1 定位报错位置