Entity Framework left outer join not working - wcf

Question

I have an Entity Framework model with the following classes (I have simplified the classes for simpler viewing):
PuzzleItem
-PuzzleId (int, primary key)
-Title
PuzzleProgress
-ProgressId (int, primary key)
-PuzzleId (FK)
-UserId (FK)
In PuzzleItem I have a number of levels. The PuzzleProgress keeps track of which level the user is at by inserting a record of that level when the user completes a previous level. For a start a new user will have one entry in PuzzleProgress with PuzzleId = 1.
In my code, I am using the following statement to perform a left outer join, so that I will get a list of all puzzles, and indicating to me which puzzle has not been solved. I made reference to this post from StackOverflow.
Here is my code:
var result = from pzs in e.PuzzleItems
join prg in e.PuzzleProgresses on pzs equals prg.PuzzleItem
into pzs_prg_tbl
from pzs_prg in pzs_prg_tbl.DefaultIfEmpty()
where pzs_prg.UserId == userId
select new SimplePuzzleItem()
{
PuzzleId = pzs_prg.PuzzleId,
PuzzleName = pzs_prg.PuzzleItem.Title,
IsUnlocked = (pzs_prg == null?false:true)
};
After running the code, only the first level of this new user is returned (while the PuzzleItem table has 3 records).
I've tried playing around with the code but the one I pasted above is the nearest I can get to, can anybody point me in the correct direction? Thanks!

Answer 1

It's a bit hard to say exactly without seeing more of the code, but where pzs_prg.UserId == userId is probably negating the left outer join.
What I mean is, if you're intending PuzzleItems LEFT JOIN PuzzleProgress then you want all PuzzleItems even when there is no PuzzleProgress. But the where pzs_prg.UserId == userId means PuzzleProgress cannot be null, because it must have a UserId (of value userId). So, you effectively have an inner join.
Personally, I don't like the "correct" way of doing joins (left or inner) in linq, so this is how I would correct the linq statement:
var result = from pz in db.PuzzleItems
from pg in db.PuzzleProgresses
.Where(pg => pg.PuzzleId == pz.PuzzleId)
.Where(pg => pg.UserId == userId)
.DefaultIfEmpty()
select new
{
PuzzleId = pz.PuzzleId,
PuzzleName = pz.Title,
IsUnlocked = (pg != null)
};
This reads a lot more like SQL joins, which I learned a long time ago so it fits my thinking.
If you want to re-factor the join type syntax, look at this 'LINQ Joining in c# with multiple conditions'

Answer 2

I think the where clause is filtering out the records. You need to include the where clause in your left join. Like so:
var result = from pzs in e.PuzzleItems
join prg in e.PuzzleProgresses on new { pzs.PuzzleId, UserId = userId } equals new { prg.PuzzleId, prg.UserId }
into pzs_prg_tbl
from pzs_prg in pzs_prg_tbl.DefaultIfEmpty()
select new SimplePuzzleItem()
{
PuzzleId = pzs_prg.PuzzleId,
PuzzleName = pzs_prg.PuzzleItem.Title,
IsUnlocked = (pzs_prg == null?false:true)
};