faster take n record in linq

Question

please see this query

return ContextDb.TestTbl.AsNoTracking().Where(x =>
                x.Field1 == newsPaperGroupId).OrderByDescending(x => x.ShowDateTime).Take(count).ToList();

Is it fetch all record then take n record?

Is there any faster way to do this query?

Answer 1

LINQ uses deferred execution, which means that it doesn't retrieve results right away - not until you call certain methods like ToList(), Single(), Count(), or iterate over the query with a foreach loop, etc.

If your query looked like this, then it'd actually be grabbing all the records where Field1 == newsPaperGroupId before taking count into consideration.

return ContextDb.TestTbl.AsNoTracking()
                .Where(x => x.Field1 == newsPaperGroupId)
                .OrderByDescending(x => x.ShowDateTime)
                .ToList()
                .Take(count);

And if it looked like this, then it'd be grabbing everything in TestTbl (ouch) before applying the filter or limiting the number of records taken.

return ContextDb.TestTbl.AsNoTracking()
                .ToList()
                .Where(x => x.Field1 == newsPaperGroupId)
                .OrderByDescending(x => x.ShowDateTime)
                .Take(count);

But what you've got looks fine. It doesn't retrieve the actual data until you've applied the filter and limited the number of records to retrieve.