How does AsQueryable() work internally?

Question

Maybe it's simple question, but does AsQueryable() have some performance loss?

Generally speaking we are working with RavenDB and we have existing code like this

protected override IQueryable<T> QueryableIndexRawQuery(string rawQuery, int skip = 0, int take = 128, string indexName = null) 
{ 
    var defaultIndexName = !string.IsNullOrWhiteSpace(indexName) ? indexName : string.Format("{0}{1}", typeof(T).Name, IndexPreffix);

    return this.Session.Advanced.DocumentStore.DatabaseCommands.GetIndex(defaultIndexName) != null 
        ? this.Session.Advanced.LuceneQuery<T>(defaultIndexName).Statistics(out this.Statistics).Skip(skip).Take(take).Where(rawQuery).AsQueryable()
        : this.Session.Advanced.LuceneQuery<T>().Statistics(out this.Statistics).Skip(skip).Take(take).Where(rawQuery).AsQueryable();
}

So Where clause return us IDocumentQuery then we try to represent it AsQueryable()

this.Session.Advanced.LuceneQuery<T>(defaultIndexName).Statistics(out this.Statistics).Skip(skip).Take(take).Where(rawQuery)

The question what AsQueryable() eventually does internally? How does it convert it? Answers with in-memory collection examples like List<> will be really useful as well.

Like this:

    var list = new List<string>() { "1", "2", "3" };
    list.AsQueryable();

This is complicated, but it's [explained somewhat by Jon Skeet on this page](http://msmvps.com/blogs/jon_skeet/archive/2011/02/20/reimplementing-linq-to-objects-part-43-out-of-process-queries-with-iqueryable.aspx). — Matthew Watson, Apr 15 '13 at 12:05

score 1 · Answer 1 · answered Apr 16 '13 at 05:22

1

.AsQueryable() forces us to evaluate the query in memory, since you are using session.Advanced.LuceneQuery(). This is NOT recommended. You need to use session.Query() if you want to use IQueryable.

answered Apr 16 '13 at 05:22

Ayende Rahien

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Ok, we are LuceneQuery because we need to server side filtering, which is pretty completecated. For example, how can we do such filtering with session.Query() - var query = _session.Advanced.LuceneQuery().Where("(Name:(*ontra*)) AND (LabelKey:(*ontra*)) OR (DescriptionKey:(*ontra*) AND (LabelKey: (*tra*)))").ToList(); We can use Search() method, but it is not suitable for composite conditions. Maybe it is another question, but the initial one was raised by it. – Jevgenij Nekrasov Apr 16 '13 at 07:53

How does AsQueryable() work internally?

1 Answers1