EF6异步包含的实体属性是否为null？

Question

Here is the query:

using (var _context = GetCommonDataContext())
    {
        return await _context.AnswerSelectListEntries
            .Include(asle => asle.Optional)
            .OrderBy(asle => asle.DisplayOrder)
            .Select(asle => new AnswerSelectListEntryDTO()
            {
                Id = asle.Id,
                AnswerSelectListId = asle.AnswerSelectListId,
                ShortAnswer = asle.ShortAnswer,
                LongAnswer = asle.LongAnswer,
                CounterpartyGroupId = asle.CounterpartyGroupId,
                Optional = new AnswerDefDTO()
                {
                    Id = asle.Optional.Id,
                    Name = asle.Optional.Name,
                    AnswerType = asle.Optional.AnswerType,
                    MultiplierAnswerType = asle.Optional.MultiplierAnswerType,
                    IntRangeLow = asle.Optional.IntRangeLow,
                    IntRangeHigh = asle.Optional.IntRangeHigh,
                    AnswerSelectListId = asle.Optional.AnswerSelectListId
                },
                AnswerDefId = asle.AnswerDefId,
                PartyType = asle.PartyType,
                DisplayOrder = asle.DisplayOrder
            }).ToListAsync();
    }

I am getting an error (thrown from the subquery) that Id, and AnswerType (which is an enum) cannot be cast to their counterparts (int and enum) because they are null. The issue is that they are non-nullable (and not null in the db). Somehow, asle.Optional's properties are being set to null (even though they are non-nullable). I am guessing this has something to do with the async but not sure what.

Fixed using:

Optional = asle.Optional == null ? null : new AnswerDefDTO()...

Answer 1

My guess would be that, since that thing is optional, and is making some kind of join, most likely a left join in the database, that the columns are coming back as DBNull simply because they weren't actually in the database. I would advise you to run a SELECT * FROM Optional where ID = whatever asle.Id is.