需要将LINQ查询从Normal JOIN转换为RIGHT OUTER JOIN

Question

I have the following query:

var poll = entities.Polls.Join(entities.Descriptors, p => p.DescriptorID, q => q.ID, (p, q) => new
                {
                    Poll = p,
                    Descriptor = q
                }).Join(entities.Media1, p => p.Descriptor.MediaID, q => q.ID, (p, q) => new
                    {
                        Poll = p.Poll,
                        Descriptor = p.Descriptor,
                        Media = q

                    }).Join(entities.PollCommentSettings,p => p.Poll.ID,q => q.PollID,(p,q) => new
                        {
                            Poll = p.Poll,
                            Descriptor = p.Descriptor,
                            Media = p.Media,
                            CommentSettings = q
                        }).FirstOrDefault(p => p.Poll.ID == request.PollID);

The problem I am having is that two of the tables that are being joined on might not have an object, but I do not care, and want to still create my top level object.

The two PollCommentSettings and Media1 tables cause this to return nothing if there is no match. What I need to have is the final object to just set these to null if they were not found. I believe this is a right outer join on both of these tables.

Answer 1

I think I figured out how to accomplish what I need by trying some stuff out in LINQpad. I got the following query which I believe accomplishes what I am looking for.

from poll in Polls join descriptor in Descriptors on poll.DescriptorID equals descriptor.ID into pdj
from descriptor in pdj.DefaultIfEmpty()
join media in Media1 on descriptor.MediaID equals media.ID into dmj
from media in dmj.DefaultIfEmpty()
join commentSetting in PollCommentSettings on poll.ID equals commentSetting.PollID into  pcj
from commentSetting in pcj.DefaultIfEmpty()
where poll.ID == 28
select new
{
    poll,
    descriptor,
    media,
    commentSetting
}