Cannot use same property for multiple relations.

[atrauzzi]

Until polymorphic relations can be supported, I am trying to take an existing schema and create some useful navigation properties out of it. Unfortunately, I've been thwarted on a number of fronts, although it feels like the closest I've been able to get is via something along these lines:

    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);

            // ...

I can't seem to retrieve anything when using something like:

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

Entity framework generates a valid query (.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

Running the generated SQL returns the correct data, but any attempt to run .First() on the query object seems to cause issues:

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)

[atrauzzi]

I'm quite blocked by this at the moment, so I've mirrored this issue to Stack Overflow.

Ahh, PEBKAC! I totally forgot about configuring my own dang value type. All fixed now.