When querying a collection using linq it always returns a null

Question

When querying a collection using linq it always returns a null

Collection<JCTransLabour> oJCTransLabours = null;

oJCTransLabour = HttpContext.Current.Session["CurrentLabourTransactions"] as 
                                  Collection<JCTransLabour>;

// at this point the collection oJCTransLabours contains 3500 records

var oCurrentLabourTrans = from clt in oJCTransLabours
                          where clt.TransactionDate.Date != DateTime.Now.Date
                          select clt;

// at this point the collection oJCTransLabour = null
// I have tried to search on different fields 

return oCurrentLabourTrans;

There must be something I am doing wrong. Any help would be very much appreciated.

Answer 1

This doesn't look like a linq issue, but rather that the value in the session is either null or not a Collection<JCTransLabour>.

You could ensure it is not null by changing the lookup to:

oJCTransLabour = (HttpContext.Current.Session["CurrentLabourTransactions"] as Collection<JCTransLabour>) ?? new Collection<JCTransLabour>();

If there should always be a session value then you could throw an exception if the value was not found before doing the query.

Answer 2

try this:

var oCurrentLabourTrans = (from clt in oJCTransLabours where clt.TransactionDate.Date != DateTime.Now.Date select clt).ToList();

Answer 3

I think you are just confusing variable names:

// You were missing an 's' before
oJCTransLabours = HttpContext.Current.Session["CurrentLabourTransactions"] 
                                    as Collection<JCTransLabour>;

Answer 4

There's at least one typo in your question.
You state that after

oJCTransLabour = HttpContext.Current.Session["CurrentLabourTransactions"] as Collection<JCTransLabour>;

oJCTransLabour is not null, right? This makes sense if session contains it.

Then you define oCurrentLabourTrans and assign LINQ query to it. And then you say that

// at this point the collection oJCTransLabour = null

Wait, how can it be null? You didn't even modify it (it was oCurrentLabourTrans modified) and you just said oJCTransLabour is not null!

Update: I just noticed there's type in names too: you call it oJCTransLabours, then you call it oJCTransLabour. Please post the exact code so we don't make assumptions about what exactly you might've mistyped.

And, of course, LINQ expression can't be null. I think it is most likely that oJCTransLabours is null though you state the otherwise.

The reason you think so, perhaps, is because you're sure HttpContext.Current.Session["CurrentLabourTransactions"] is not null. This is true, but you use as operator to cast the value to Collection<JCTransLabour>. As opposed to casting operator, as doesn't throw an exception if types mismatch, it just returns null.

You might want to try

oJCTransLabour = (Collection<JCTransLabour>)HttpContext.Current.Session["CurrentLabourTransactions"];

and see if any errors show up.