在其他模型上为多个导航属性重用外键

Question

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

---

直到polymorphic relations can be supported，我正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，我在许多方面都受到了挫败，尽管感觉我能得到的最接近的方法是通过以下方式：

    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);

            // ...

使用类似的东西时我似乎无法检索任何东西：

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

实体框架生成有效查询 (.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，但任何尝试在查询对象上运行 .First(), FirstOrDefault(), etc... 似乎都会导致问题：

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 , QueryContext , DbDataReader , ResultContext , 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, Task lastTask, State next, Scope scope, Object state, 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)

Answer 1

看起来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 扩展的代码。