如何解决EF Core (usdig Raw Sql) 中的 System.InvalidCastException 错误，当查询不返回行时但在查询返回行时工作
在 .Net 5 Web Api 应用程序中，我正在从 MysqL 表中读取一些行（使用 Pomelo 库）。 我正在使用原始 sql 查询。所以：
MysqLParameter propertyIdParam = new MysqLParameter()
{
ParameterName = "@propertyId",MysqLDbType = MysqLDbType.Int32,Direction = System.Data.ParameterDirection.Input,Value = 7
};
List<PropertyRepairsDto> propertyRepairs = await _context.PropertyRepairs
.FromsqlRaw("some sql query",propertyIdParam)
.AsNoTracking()
.ToListAsync();
奇怪的是，这很有效，直到我提供了一个不存在的参数（“propertyId”） - 以便查询不返回任何行。在这种情况下，我收到以下异常：
system.invalidCastException: Specified cast is not valid.
at MysqLConnector.Core.Row.GetInt32(Int32 ordinal) in /_/src/MysqLConnector/Core/Row.cs:line 211
at MysqLConnector.MysqLDataReader.GetInt32(Int32 ordinal) in /_/src/MysqLConnector/MysqLDataReader.cs:line 238
at lambda_method848(Closure,QueryContext,DbDataReader,Int32[] )
at Microsoft.EntityFrameworkCore.Query.Internal.FromsqlQueryingEnumerable`1.AsyncEnumerator.MoveNextAsync()
at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable`1 source,CancellationToken cancellationToken)
at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable`1 source,CancellationToken cancellationToken)
at PropWorx.API.Controllers.PropertiesController.GetPropertyRepairsAsync(Int32 id) in C:\Users\fabsr\source\repos\PropWorx.API\PropWorx.API\Controllers\PropertiesController.cs:line 194
at lambda_method479(Closure,Object )
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(IActionResultTypeMapper mapper,ObjectMethodExecutor executor,Object controller,Object[] arguments)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Logged|12_1(ControllerActionInvoker invoker)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterasync>g__Awaited|10_0(ControllerActionInvoker invoker,Task lastTask,State next,Scope scope,Object state,Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next,Scope& scope,Object& state,Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterasync>g__Awaited|13_0(ControllerActionInvoker invoker,Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker,Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint,Task requestTask,ILogger logger)
at PropWorx.API.Middlewares.TenantIdentifier.Invoke(HttpContext httpContext,SharedContext sharedContext) in C:\Users\fabsr\source\repos\PropWorx.API\PropWorx.API\Middlewares\TenantIdentifier.cs:line 52
at PropWorx.API.Middlewares.WebSocketsMiddleware.Invoke(HttpContext httpContext) in C:\Users\fabsr\source\repos\PropWorx.API\PropWorx.API\Middlewares\WebSocketsMiddleware.cs:line 28
at Microsoft.AspNetCore.Authorization.Policy.AuthorizationMiddlewareResultHandler.HandleAsync(RequestDelegate next,HttpContext context,AuthorizationPolicy policy,PolicyAuthorizationResult authorizeResult)
at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Session.SessionMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Session.SessionMiddleware.Invoke(HttpContext context)
at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext,ISwaggerProvider swaggerProvider)
at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
HEADERS
=======
Connection: keep-alive
Content-Type: application/json
Accept: */*
Accept-Encoding: gzip,deflate,br
Authorization: Bearer eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6Ik1ERXpSRUUwUWpFMk9VTkdOa0kyUlRJMFJEUXdNakExUTBFeE1EUkNRalpDUmtWR1JVTXhOQSJ9.eyJpc3MiOiJodHRwczovL2NvZGV4Y3JlYXRpb25zLmV1LmF1dGgwLmNvbS8iLCJzdWIiOiJhdXRoMHw1OTI2YjEwYTAxZTkxZDE0MGU5OWVlNjQiLCJhdWQiOlsiaHR0cHM6Ly9wcm9wd29yeC5jby56YS9hcGkiLCJodHRwczovL2NvZGV4Y3JlYXRpb25zLmV1LmF1dGgwLmNvbS91c2VyaW5mbyJdLCJpYXQiOjE2MTAwMDkyMjQsImV4cCI6MTYxMjYwMTIyNCwiYXpwIjoiUnppNzVkU1dpcVlFYlJsVjU1N0lFd1dQYUI5Qmwzd3giLCJzY29wZSI6Im9wZW5pZCBwcm9maWxlIGVtYWlsIn0.WK2gtsbWtiz1WIkJrO56Ap8fqyyyLBs1wiKcs0KvTVTPKlzVyicf6J9S-9PMDGs1uT-gho7fVW6gLVv9XzLCulcR4x3KFrNmLSW9lvsj9fyKPMQ4Udp4A2UdfYoogRXdub62QwqRhkYGbNkI-tSGgMwF-zgClirKalpY6oKs9yMY6qr_XC4ZzTI27Pd4W9wverLtLT0-1WNlh4ynUF_xE5uvfKfh0KhBITs-KASUBMz7WcloSehNqvnkwOOdLccwtkcbcms4LRklwEzpQvXiuCwAgjpjq980fjFjYSISjD5paqBM_rdpvG4Yz4OqI6FXtccuszbc_1WcXe7O_CSuTg
Host: localhost:5001
Referer: http://localhost:5000/api/properties/6823/repairs
User-Agent: PostmanRuntime/7.26.8
Content-Length: 2856
clientId: 273
Postman-Token: fe2fcc49-3f1b-451b-8e06-b808fa28964c
我不明白当查询返回行时它如何正常工作（因此它将数据库数据正确映射到模型字段），但是当查询不返回行时（我认为应该只是导致零项的列表）它会引发异常。
该异常表明将值从数据库转换为 int32 时出现问题。起初，我认为它可能是一个空值，它试图映射到我的模型中的一个不可为空的整数，但我的模型中的所有整数字段都是可以为空的。但即便如此，由于查询没有返回任何行，所以肯定不会有问题，因为没有什么可映射的吗？
我知道没有看到数据库结构、模型、查询等很难帮助我。只是查询和表相当大，我想也许之前有人遇到过这个问题，直到查询才起作用调用不返回任何行，在这种情况下抛出 system.invalidCastException。
这是我要映射到的模型，它的价值：
public class PropertyRepairsDto
{
public int? Id { get; set; }
public int? FileId { get; set; }
public string FileNum { get; set; }
public bool? Isrequired { get; set; }
public string Info { get; set; }
public bool? QuotesObtained { get; set; }
public decimal? QuoteAmount { get; set; }
public string ContractorAppointed { get; set; }
public bool? IsPaid { get; set; }
public decimal? AmountPaid { get; set; }
public DateTime? JobDate { get; set; }
public bool? Paymentrequired { get; set; }
public DateTime? PaymentDate { get; set; }
public string PaymentReference { get; set; }
public DateTime? ReportedAt { get; set; }
public int? ContractorId { get; set; }
public string Contractor { get; set; }
public bool? IsFixedByOwner { get; set; }
public DateTime? FollowUpDate { get; set; }
public string WorkOrderNumber { get; set; }
public bool? IsCompleted { get; set; }
public DateTime? CompletedDate { get; set; }
public bool? IsInvoiceReceived { get; set; }
public DateTime? InvoiceReceivedAt { get; set; }
public decimal? InvoiceAmount { get; set; }
public bool? IsInvoiceApproved { get; set; }
public DateTime? InvoiceApprovedAt { get; set; }
public string InvoiceApprovedBy { get; set; }
public bool? ChargetoTenant { get; set; }
public bool? IsReportedToOwner { get; set; }
public DateTime? ReportedToOwnerAt { get; set; }
public int? InvoiceDocId { get; set; }
public int? ReportedById { get; set; }
public string ReportedBy { get; set; }
public int? PriorityId { get; set; }
public string Priority { get; set; }
public int? Quotesrequired { get; set; }
public bool? InvoiceOwner { get; set; }
public bool? InvoiceTenant { get; set; }
public bool? IsReportSentToTenant { get; set; }
public DateTime? ReportSentToTenantAt { get; set; }
public bool? IsJobCardSentToServiceProvider { get; set; }
public int? JobCardSentToId { get; set; }
public string JobCardSentTo { get; set; }
public int? JobCardSentToServiceProviderById { get; set; }
public string JobCardSentToServiceProviderBy { get; set; }
public DateTime? JobCardSentToServiceProviderAt { get; set; }
public int? StatusId { get; set; }
public string Status { get; set; }
public int? PropertyId { get; set; }
public int? AssignedToId { get; set; }
public string AssignedTo { get; set; }
public string Comments { get; set; }
public DateTime? AddedAt { get; set; }
public DateTime? ModifiedAt { get; set; }
}
解决方法
我无法复制这种行为。我更新并使用了以下示例代码，其中包括您在评论中提到的 def replace_function(sequence):
for i in sequence:
string = sequence.replace("A","-BF+AFA+FB-").replace("B","+AF-BFB-FA+")
return string
replace_function("AB")
>>> -+AF-BFB-FA+F+AFA+F+AF-BFB-FA+-+AF-BFB-FA+
聚合函数，该函数在 Pomelo replace_function("AB")
>>> -BF+AFA+FB-+AF-BFB-FA+
中没有问题：
GROUP_CONCAT为了帮助您，我们需要更多信息：
- 确切的 LINQ 查询（包括您在 FromSqlRaw() 调用中使用的确切 SQL 查询）
- 数据库服务器类型（例如
5.0.0-alpha.2或using System.Diagnostics; using System.Linq; using Microsoft.EntityFrameworkCore; using Microsoft.Extensions.Logging; using MySqlConnector; using Pomelo.EntityFrameworkCore.MySql.Infrastructure; namespace IssueConsoleTemplate { public class IceCream { public int IceCreamId { get; set; } public string Name { get; set; } public string Company { get; set; } public string FullName { get; set; } } public class Context : DbContext { public virtual DbSet<IceCream> IceCreams { get; set; } protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) { var connectionString = "server=127.0.0.1;port=3306;user=root;password=;database=So65847111_GroupConcat"; optionsBuilder.UseMySql( connectionString,ServerVersion.AutoDetect(connectionString),options => options.CharSetBehavior(CharSetBehavior.NeverAppend)) .UseLoggerFactory( LoggerFactory.Create( configure => configure .AddConsole() .AddFilter(level => level >= LogLevel.Information))) .EnableSensitiveDataLogging() .EnableDetailedErrors(); } protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity<IceCream>( entity => { entity.Property(e => e.Name) .HasDefaultValue("Vanilla"); entity.HasData( new IceCream {IceCreamId = 1,Name = "Vanilla",Company = "Icecold"},new IceCream {IceCreamId = 2,Name = "Chocolate",Company = "Mr IceCream"}); }); } } internal static class Program { private static void Main(string[] args) { using var context = new Context(); context.Database.EnsureDeleted(); context.Database.EnsureCreated(); var iceCreamIdParameter = new MySqlParameter { ParameterName = "@iceCreamIdParam",MySqlDbType = MySqlDbType.Int32,Direction = System.Data.ParameterDirection.Input,Value = 42,// <-- does not exist }; var iceCreams = context.IceCreams .FromSqlRaw(@" SELECT `IceCreamId`,`Name`,`Company`,GROUP_CONCAT(`Name`,`Company` SEPARATOR ',') AS `FullName` FROM `IceCreams` WHERE `IceCreamId` = @iceCreamIdParam GROUP BY `IceCreamId`,`Company`",iceCreamIdParameter) .AsNoTracking() .ToList(); Trace.Assert(iceCreams.Count == 0); } } }）及其确切版本（例如MySQL）
（只需使用请求的信息更新 OP。）
异常提示，您返回的字段之一不包含应有的类型（或可为空性）：
System.InvalidCastException：指定的强制转换无效。 在 MySqlConnector.Core.Row.GetInt32(Int32 ordinal)
所以您的查询需要一个 MariaDB，但返回的值是别的东西。
在 8.0.21 中抛出异常时让您的调试器中断并检查它尝试转换为 Int32 的值。然后检查方法的 Row.GetInt32() 参数。最后，检查与 EF Core 生成的 SQL 查询中 Int32 参数相同位置的表达式（您应该在堆栈中 ordinal 对象的 ordinal 属性中找到它，或者您可以使用 EF Core 记录它）。
除此之外，您还可以运行我发布在您服务器上的代码。它应该可以完美地工作。如果不是，那么这应该与一些意外的 MySQL 服务器设置有关。
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