ThenInclude fails with ArgumentNullException for the navigation of base class which is not added as entity type

[zilloy]

I have the following classes

public class ClassA
    {
        public ICollection<ClassB> BItems { get; set; }
    }

public class ClassB: GenericClass<ClassA>
    {

    }

public class GenericClass<T>
    {
        public ICollection<ClassC> CItems{ get; set; }
    }

public class ClassC
    {

    }

When I try to execute the following statement it fails with ArgumentNullException

return _dbContext.Set<ClassA>()
                .Include(x => x.BItems)
                .ThenInclude(x => x.CItems)
                .SingleOrDefaultAsync(x => x.Id == id, cancellationToken);

Here is the stack trace

   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.<>c__DisplayClass43_0.<IncludeNavigations>b__1(IEnumerable`1 ps, IQuerySource _)
   at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.BindMemberExpressionCore[TResult](MemberExpression memberExpression, IQuerySource querySource, Func`3 memberBinder)
   at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.BindNavigationPathMemberExpression[TResult](MemberExpression memberExpression, Func`3 memberBinder)
   at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.<IncludeNavigations>b__43_0(IncludeQueryAnnotation annotation)
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
   at System.Linq.OrderedEnumerable`1.<GetEnumerator>d__1.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.IncludeNavigations(QueryModel queryModel)
   at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.CreateAsyncQueryExecutor[TResult](QueryModel queryModel)
   at Microsoft.Data.Entity.Storage.Database.CompileAsyncQuery[TResult](QueryModel queryModel)
   at Microsoft.Data.Entity.Query.QueryCompiler.<>c__DisplayClass17_0`1.<CompileAsyncQuery>b__0()
   at Microsoft.Data.Entity.Query.Internal.CompiledQueryCache.GetOrAddAsyncQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.Data.Entity.Query.QueryCompiler.CompileAsyncQuery[TResult](Expression query)
   at Microsoft.Data.Entity.Query.QueryCompiler.ExecuteAsync[TResult](Expression query, CancellationToken cancellationToken)
   at Microsoft.Data.Entity.Query.Internal.EntityQueryProvider.ExecuteAsync[TResult](Expression expression, CancellationToken cancellationToken)
   at Microsoft.Data.Entity.EntityFrameworkQueryableExtensions.ExecuteAsync[TSource,TResult](MethodInfo operatorMethodInfo, IQueryable`1 source, Expression expression, CancellationToken cancellationToken)
   at Microsoft.Data.Entity.EntityFrameworkQueryableExtensions.ExecuteAsync[TSource,TResult](MethodInfo operatorMethodInfo, IQueryable`1 source, LambdaExpression expression, CancellationToken cancellationToken)
   at Microsoft.Data.Entity.EntityFrameworkQueryableExtensions.SingleOrDefaultAsync[TSource](IQueryable`1 source, Expression`1 predicate, CancellationToken cancellationToken)

EDIT: It also failed when I tried to make GenericClass non-generic. I guess it happened because of CItems collection

[rowanmiller]

Repro'd on the latest bits. Seems to be related to having a navigation defined on an unmapped base type. Below is a runnable repro. If BaseClass is pulled into the model, then the query succeeds. It's also not as basic as just including any nav prop on an unmapped base type, as querying for ClassB and Including CItems works fine.

using Microsoft.Data.Entity;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApp1
{
    public class Program
    {
        public static void Main(string[] args)
        {
            using (var db = new SampleContext())
            {
                db.Database.EnsureDeleted();
                db.Database.EnsureCreated();

                var a = new ClassA
                {
                    BItems = new List<ClassB>
                    {
                        new ClassB
                        {
                            CItems = new List<ClassC>
                            {
                                new ClassC()
                            }
                        }
                    }
                };

                db.Add(a);
                db.Add(a.BItems.Single());
                db.Add(a.BItems.Single().CItems.Single());
                db.SaveChanges();
            }

            using (var db = new SampleContext())
            {
                var id = 1;

                var a = db.Set<ClassA>()
                    .Include(x => x.BItems)
                    .ThenInclude(x => x.CItems)
                    .SingleOrDefaultAsync(x => x.Id == id);
            }
        }
    }

    public class SampleContext : DbContext
    {
        public DbSet<ClassA> ClassAs { get; set; }
        public DbSet<ClassB> ClassBs { get; set; }
        public DbSet<ClassC> ClassCs { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder builder)
        {
            builder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=Samples;Trusted_Connection=True;");
        }
    }

    public class ClassA
    {
        public int Id { get; set; }
        public ICollection<ClassB> BItems { get; set; }
    }

    public class ClassB : BaseClass
    {
    }

    public class BaseClass
    {
        public int Id { get; set; }
        public ICollection<ClassC> CItems { get; set; }
    }

    public class ClassC
    {
        public int Id { get; set; }
    }
}

[smitpatel]

The issue is when we work with chained navigations, we find the declaring type in our model to get the navigation from property info. If the navigation is declared on base type which is not included in the model then navigation is not found and ArgumentNullException is thrown.