I was trying to get the following to work (Northwind):

                var q1 =
                    from o in db.Orders
                    select new {
                        o.OrderID,
                        HasRegion = (o.ShipRegion == null) ? true : false
                    };

                var q2 = q1.Where(a => a.HasRegion == true).ToList();

but it blew up with yet another alias error.

Msg 4145, Level 15, State 1, Line 9
An expression of non-boolean type specified in a context where a condition is expected, near 'THEN'.
Msg 102, Level 15, State 1, Line 17
Incorrect syntax near 'LPA_L1'.

this was from the following sql

exec sp_executesql N'
SELECT [LPA_L1].[OrderID], [LPA_L1].[LPFA_5] 
FROM 
(
    SELECT [LPLA_1].[OrderID], CASE WHEN CASE WHEN CASE WHEN 
    (
        [LPLA_1].[ShipRegion] IS NULL
    ) 
    THEN 1 ELSE 0 END=1 THEN @LO11 ELSE @LO02 END THEN 1 ELSE 0 END AS [LPFA_5] 
    FROM [Northwind].[dbo].[Orders] [LPLA_1] 
) 
LPA_L1 WHERE 
( 
    ( 
        ( 
            ( 
                [LPA_L1].[HasRegion] = @HasRegion3
            )
        )
    )
)
',N'@LO11 bit,@LO02 bit,@HasRegion3 bit',@LO11=1,@LO02=0,@HasRegion3=1

This is interesting also because I was trying to reproduce an error I was having in another piece of work in Northwind, but I got a different error, saying the equivalent of Invalid column name 'HasRegion'. I will see if I can get this one to reproduce in Northwind too, but I havent managed yet.

Thanks! Ross

BTW: I appreciate that true and false are essentially the wrong way around but you get the idea

Some unwanted CASE statements are emitted there. This can be due to the fact that the expression is in a projection: boolean expressions in the projection aren't supported in SQL. I'll check where this extra wrapper is coming from. (and also why the column isn't properly aliased to HasRegion)

To be able to handle select new { o.OrderID, HasRegion = (o.ShipRegion == null) };

it can't assume the case always returns 1. So I had to make it look like another boolean (real boolean, not 1 or 0), and then it worked. At least, it then ran into the field alias issue, which is now on the table.

Fixed in next build.