I can't add a defining query that uses a left join

[ChannelSix]

If I create a defining query that uses a left join in EF Core v3.1.1 I get the exception below when attempting to query the defining query. Note that I can't use navigation properties on my actual models.

If I run the exact same expression through a normal query it runs fine.

Steps to reproduce

    class Program
    {
        static async Task Main(string[] args)
        {
            var context = new Context();
            var adHocQuery = from p in context.Set<Parent>()
                        join c in context.Set<Child>() on p.Id equals c.ParentId into outer
                        from cLeft in outer
                        select new ParentChild
                        {
                            ParentId = p.Id,
                            ParentName = p.Name,
                            ChildId = cLeft == null ? (int?)null : cLeft.Id,
                            ChildName = cLeft == null ? null : cLeft.Name
                        };
            var adHocQueryResult = await adHocQuery.ToArrayAsync();
            var joined = await context.Set<ParentChild>().ToArrayAsync();
        }
    }

    public class Parent
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

    public class Child
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int ParentId { get; set; }
    }

    public class ParentChild
    {
        public int ParentId { get; set; }
        public string ParentName { get; set; }
        public int? ChildId { get; set; }
        public string ChildName { get; set; }
    }

    public class Context : DbContext
    {
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Parent>()
                .HasKey(p => p.Id);
            modelBuilder.Entity<Child>()
                .HasKey(c => c.Id);

            modelBuilder.Entity<ParentChild>()
                .HasNoKey()
                .ToQuery(() =>
                    from p in Set<Parent>()
                    join c in Set<Child>() on p.Id equals c.ParentId into outer
                    from cLeft in outer
                    select new ParentChild
                    {
                        ParentId = p.Id,
                        ParentName = p.Name,
                        ChildId = cLeft == null ? (int?)null : cLeft.Id,
                        ChildName = cLeft == null ? null : cLeft.Name
                    }
            );
        }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            base.OnConfiguring(optionsBuilder);
            optionsBuilder
                .UseSqlServer("server=(local);Database=EFDefiningQueryLeftJoin;Integrated Security=SSPI;")
                .UseQueryTrackingBehavior(QueryTrackingBehavior.NoTracking);
        }
    }

Exception:

System.InvalidOperationException: 'Processing of the LINQ expression 'DbSet
.GroupJoin(
outer: DbSet,
inner: p => p.Id,
outerKeySelector: c => c.ParentId,
innerKeySelector: (p, outer) => new {
p = p,
outer = outer
})' by 'NavigationExpandingExpressionVisitor' failed. This may indicate either a bug or a limitation in EF Core. See https://go.microsoft.com/fwlink/?linkid=2101433 for more detailed information.'

Further technical details

EF Core version: 3.1.1
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework:. NET Core 3.1
Operating system: Windows 10
IDE: Visual Studio 2019 16.4.4

[ajcvickers]

@maumar to take a look.

[maumar]

dupe of #19708

[maumar]

@ChannelSix you can use QueryableExtensions.LeftJoin method directly as a workaround:

                modelBuilder.Entity<ParentChild>()
                    .HasNoKey()
                    .ToQuery(() =>
                        Set<Parent>().LeftJoin(Set<Child>(), k => k.Id, k => k.ParentId, (p, cLeft) => new ParentChild
                        {
                            ParentId = p.Id,
                            ParentName = p.Name,
                            ChildId = cLeft == null ? (int?)null : cLeft.Id,
                            ChildName = cLeft == null ? null : cLeft.Name
                        }));

QueryableExtensions is defined in Microsoft.EntityFrameworkCore.Internal namespace

[ChannelSix]

Thanks for looking at this and the suggestion.