Query :: error during groupjoin flattening for complex query with multiple joins subquery and LOJ

[maumar]

query:

from qRoot in ctx.Questions
join qAnswered in
(
    from instance in ctx.ExamInstances
    join answered in ctx.ExamInstanceQuestions
        on instance.StudentId equals 1
    join qVersion in ctx.Questions on answered.QuestionId equals qVersion.Id
    select qVersion
)
    on qRoot.Id equals qAnswered.RootQuestionId ?? qAnswered.Id
    into AnsweredQuestions
from qAnswered in AnsweredQuestions.DefaultIfEmpty()
select qRoot;

model:

        public class MyContext : DbContext
        {
            public DbSet<Question> Questions { get; set; }
            public DbSet<ExamInstance> ExamInstances { get; set; }
            public DbSet<ExamInstanceQuestion> ExamInstanceQuestions { get; set; }
        }

        public class Question
        {
            public int Id { get; set; }
            public int? RootQuestionId { get; set; }
            public DateTime Version { get; set; }
            public Question3582 RootQuestion { get; set; }
        }

        public class ExamInstance
        {
            public int Id { get; set; }
            public int StudentId { get; set; }
        }

        public class ExamInstanceQuestion
        {
            public int Id { get; set; }
            public int ExamInstanceId { get; set; }
            public int QuestionId { get; set; }
            public int? AnswerId { get; set; }
            public ExamInstance3582 ExamInstance { get; set; }
            public Question3582 Question { get; set; }
        }

Expression that is being flatten:

IEnumerable<TransparentIdentifier<Question3582, IEnumerable<ValueBuffer>>> _GroupJoin(
    outer: IEnumerable<Question3582> _ShapedQuery(
        queryContext: Unhandled parameter: queryContext, 
        shaperCommandContext: SelectExpression: 
            SELECT [qRoot].[Id], [qRoot].[RootQuestionId], [qRoot].[Version], [t].[RootQuestionId], [t].[Id]
            FROM [Questions] AS [qRoot]
            LEFT JOIN (
                SELECT [qVersion0].*
                FROM [ExamInstances] AS [instance0]
                INNER JOIN [ExamInstanceQuestions] AS [answered0] ON [instance0].[StudentId] = 1
                INNER JOIN [Questions] AS [qVersion0] ON [answered0].[QuestionId] = [qVersion0].[Id]
            ) AS [t] ON [qRoot].[Id] = COALESCE([t].[RootQuestionId], [t].[Id])
            ORDER BY [qRoot].[Id]
        , 
        shaper: BufferedEntityShaper<Question3582>
    )
    , 
    inner: IEnumerable<ValueBuffer> _Select(
        source: IEnumerable<TransparentIdentifier<TransparentIdentifier<ValueBuffer, ValueBuffer>, ValueBuffer>> _ShapedQuery(
            queryContext: Unhandled parameter: queryContext, 
            shaperCommandContext: SelectExpression: 
                SELECT [t].[RootQuestionId], [t].[Id]
                FROM (
                    SELECT [qVersion0].*
                    FROM [ExamInstances] AS [instance0]
                    INNER JOIN [ExamInstanceQuestions] AS [answered0] ON [instance0].[StudentId] = 1
                    INNER JOIN [Questions] AS [qVersion0] ON [answered0].[QuestionId] = [qVersion0].[Id]
                ) AS [t]
            , 
            shaper: CompositeShaper`3
        )
        , 
        selector: (TransparentIdentifier<TransparentIdentifier<ValueBuffer, ValueBuffer>, ValueBuffer> t1) => t1.Inner
    )
    , 
    outerKeySelector: (Question3582 qRoot) => (Nullable<int>) qRoot.Id, 
    innerKeySelector: (ValueBuffer qAnswered) => (Nullable<int>) object qAnswered.get_Item(0) ?? (Nullable<int>) (int) object qAnswered.get_Item(1), 
    resultSelector: (Question3582 qRoot | IEnumerable<ValueBuffer> AnsweredQuestions) => TransparentIdentifier<Question3582, IEnumerable<ValueBuffer>> CreateTransparentIdentifier(
        outer: qRoot, 
        inner: AnsweredQuestions
    )
)

[maumar]

fixed in 9a34e1d