Question

Something very strange is happening in my program:

I make this query agt.DefaultNr == 1 on a collection and get 3 items as Result:

IEnumerable<Agent> favAgents =
            from agt in builtAgents where agt.DefaultNr == 1 select agt;

For every item I set the DefaultNr = 0

foreach (Agent noFavAgt in favAgents)
{
    noFavAgt.DefaultNr = 0;
}

I do another query but for some reason my favAgents collection is empty now!

IEnumerable<Agent> smallAgents = (from agt in favAgents
    where agt.tempResultCount < 30
    orderby agt.tempResultCount descending
    select agt);

What is going on here?

Is this a LINQ lazy loading problem?

Looks like there will be some kind of re-query after I set all items = 0 because I my collection is empty!

Answer 1

This is not lazy loading, it’s deferred execution. When you define your initial enumerable, you’re defining a query, not a collection. You’re correct that it’s performing a requery; every time you iterate over favAgents, it will execute the query that you defined. If you want to create a list based off of that query that doesn’t change, add ToList().

var favAgents = 
    (from agt in builtAgents where agt.DefaultNr == 1 select agt).ToList();

Doing this will create a list in memory and cache the results of the query at that point in time.