对其他模型的多个导航属性重复使用外键

问题描述

这是a corresponding github issue on the EF Core repo的交叉发布。

---

在polymorphic relations can be supported之前，我一直在尝试采用现有模式并从中创建一些有用的导航属性。不幸的是，尽管在感觉上我能够获得的最接近的途径是通过以下方面，但我在很多方面都受到挫败：

    public class Entitlement
    {
        public Guid Id { get; set; }
        public Guid EntitleableId { get; set; }
    }

    public class Tenant
    {
        public Guid Id { get; set; }

        public ICollection<Entitlement> AssignedEntitlements { get; set; }
    }

    // note: Consider User and Firm the same as tenant in this example.

            // ...

            modelBuilder
                .Entity<Tenant>()
                .HasMany((tenant) => tenant.AssignedEntitlements)
                .WithOne()
                .Isrequired(true)
                .HasForeignKey((entitlement) => entitlement.EntitleableId)
                .HasPrincipalKey((tenant) => tenant.Id);

            modelBuilder
                .Entity<Firm>()
                .HasMany((firm) => firm.AssignedEntitlements)
                .WithOne()
                .Isrequired(true)
                .HasForeignKey((entitlement) => entitlement.EntitleableId)
                .HasPrincipalKey((firm) => firm.Id);

            modelBuilder
                .Entity<User>()
                .HasMany((user) => user.AssignedEntitlements)
                .WithOne()
                .Isrequired(true)
                .HasForeignKey((entitlement) => entitlement.EntitleableId)
                .HasPrincipalKey((user) => user.Id);

            // ...

使用类似这样的东西时，我似乎无法检索到任何东西

dbContext.Tenants.Include((t) => t.AssignedEntitlements);

实体框架生成有效的查询（.ToQueryString()）：

SELECT t.id,t.created_at,t."default",t.deleted_at,t.label,t.name,t.updated_at,e.id,e.created_at,e.entitleable_id,e.entitleable_type,e.feature,e.source_id,e.source_type,e.updated_at
FROM tenants AS t
         LEFT JOIN entitlements AS e ON t.id = e.entitleable_id
ORDER BY t.id,e.id

运行生成的sql会返回正确的数据，但是对查询对象运行.First(),FirstOrDefault(),etc...的任何尝试似乎都会引起问题：

system.invalidOperationException: Sequence contains no matching element
   at System.Linq.ThrowHelper.ThrowNoMatchException()
   at System.Linq.Enumerable.First[TSource](IEnumerable`1 source,Func`2 predicate)
   at MyProject.Conventions.Feature..ctor(String name)
   at lambda_method374(Closure,QueryContext,DbDataReader,ResultContext,SingleQueryResultCoordinator )
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.<PopulateIncludeCollection>g__ProcessCurrentElementRow|60_0[TIncludingEntity,TIncludedEntity](<>c__displayClass60_0`2& )
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.PopulateIncludeCollection[TIncludingEntity,TIncludedEntity](Int32 collectionId,QueryContext queryContext,DbDataReader dbDataReader,SingleQueryResultCoordinator resultCoordinator,Func`3 parentIdentifier,Func`3 outerIdentifier,Func`3 selfIdentifier,IReadOnlyList`1 parentIdentifierValueComparers,IReadOnlyList`1 outerIdentifierValueComparers,IReadOnlyList`1 selfIdentifierValueComparers,Func`5 innerShaper,INavigationBase inverseNavigation,Action`2 fixup,Boolean trackingQuery)
   at lambda_method376(Closure,SingleQueryResultCoordinator )
   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
   at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source)
   at lambda_method377(Closure,QueryContext )
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
   at System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source)
   at MyProject.Global.Api.Controller.TestController.Test(MyProjectGlobalContext context) in /home/me/Development/MyProject/global/MyProject.Global.Api/src/Controller/TestController.cs:line 19
   at lambda_method289(Closure,Object )
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfActionResultExecutor.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()
--- End of stack trace from prevIoUs location ---
   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 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.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

解决方法

看起来像您的代码会导致此异常。 MyProject.Conventions.Feature构造函数包含为某些空记录集调用First扩展名的代码。