Best way to get Count for paging in ravenDB

Question

I need to find the number of documents that are in the raven database , so that I can properly page the documents out. I had the following implementation -

public int Getcount<T>()
{
    IQueryable<T> queryable = from p in _session.Query<T>().Customize(x =>x.WaitForNonStaleResultsAsOfLastWrite())
    select p;
    return queryable.Count();
}

But if the count is too large then it times out.

I tried the method suggested in FAQs -

    public int GetCount<T>()
    {
        //IQueryable<T> queryable = from p in _session.Query<T>().Customize(x => x.WaitForNonStaleResultsAsOfLastWrite())
        //                          select p;
        //return queryable.Count();

        RavenQueryStatistics stats;
        var results = _session.Query<T>()
            .Statistics(out stats);

        return stats.TotalResults;
    }

This always returns 0.

What am I doing wrong?

Thomas Freudenberg · Accepted Answer · 2015-07-05T15:02:58.717

15

stats.TotalResults is 0 because the query was never executed. Try this instead:

var results = _session
    .Query<T>()
    .Statistics(out stats)
    .Take(0)
    .ToArray();

edited Jul 05 '15 at 15:02

answered Aug 17 '11 at 13:57

Thomas Freudenberg

5,048
1
35
44

Instead of `ToArray()`, which will process all the items, use `Any()`, which will process single item only. You're not interested in payload anyway. And this has nothing to do with Raven API, it's a deferred execution in LINQ... – Jakub Konecki Feb 26 '13 at 20:57
@JakubKonecki There aren't any items because of `Take(0)`, so `ToArray()` is there just to force a server round-trip and get the total count. The response will not contain any items. – Thomas Freudenberg Mar 04 '13 at 13:02
@ThomasFreudenberg - You're right, I haven't noticed `(0)` ;-). Nice trick! – Jakub Konecki Mar 04 '13 at 14:33

biofractal · Answer 2 · 2012-09-28T12:14:08.473

The strange syntax to get the statistics tripped me up as well. I can see why the query needs to be run in order to populate the statistic object but the syntax is a bit verbose imo.

I have written the following extension method for use in my unit tests. It helps keep the code terse.

Extension Method

public static int QuickCount<T>(this IRavenQueryable<T> results)
{
    RavenQueryStatistics stats;
    results.Statistics(out stats).Take(0).ToArray();
    return stats.TotalResults;
}

Unit Test

...
db.Query<T>().QuickCount().ShouldBeGreaterThan(128);
...

Best way to get Count for paging in ravenDB

2 Answers2