Since aa is the set/object that might be null, can you check aa == null ?
(aa / xx might be interchangeable (a typo in the question); the original question talks about xx but only defines aa)
i.e.
select new {
AssetID = x.AssetID,
Status = aa == null ? (bool?)null : aa.Online; // a Nullable<bool>
}
or if you want the default to be false (not null):
select new {
AssetID = x.AssetID,
Status = aa == null ? false : aa.Online;
}
Update; in response to the downvote, I've investigated more... the fact is, this is the right approach! Here's an example on Northwind:
using(var ctx = new DataClasses1DataContext())
{
ctx.Log = Console.Out;
var qry = from boss in ctx.Employees
join grunt in ctx.Employees
on boss.EmployeeID equals grunt.ReportsTo into tree
from tmp in tree.DefaultIfEmpty()
select new
{
ID = boss.EmployeeID,
Name = tmp == null ? "" : tmp.FirstName
};
foreach(var row in qry)
{
Console.WriteLine("{0}: {1}", row.ID, row.Name);
}
}
And here's the TSQL - pretty much what we want (it isn't ISNULL, but it is close enough):
SELECT [t0].[EmployeeID] AS [ID],
(CASE
WHEN [t2].[test] IS NULL THEN CONVERT(NVarChar(10),@p0)
ELSE [t2].[FirstName]
END) AS [Name]
FROM [dbo].[Employees] AS [t0]
LEFT OUTER JOIN (
SELECT 1 AS [test], [t1].[FirstName], [t1].[ReportsTo]
FROM [dbo].[Employees] AS [t1]
) AS [t2] ON ([t0].[EmployeeID]) = [t2].[ReportsTo]
-- @p0: Input NVarChar (Size = 0; Prec = 0; Scale = 0) []
-- Context: SqlProvider(Sql2008) Model: AttributedMetaModel Build: 3.5.30729.1
QED?