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Lucene Score

Every indexed RavenDB document has an associated score value that has been calculated by Lucene. This value is really important part of the Lucene engine because it has the influence on the search results relevancy. The basic idea is that the greater score value is the more relevant document is to a query. The entire mechanism is managed by Lucene so a user does not need to care and even know about. However if you want to get more info about Lucene scoring, please follow this link.

As the RavenDB user you are able to retrieve the calculated score by asking about document metadata and using this value to order by. Let's define an index and store some items:

store.DatabaseCommands.PutIndex("Articles/ByText", new IndexDefinitionBuilder<Article, Article>
	Map = articles => from article in articles select new { article.Text },
	Indexes =
		{ x => x.Text, FieldIndexing.Analyzed }

using (var s = store.OpenSession())
	s.Store(new Article() {Text = "Lorem ipsum is simply text."}); // articles/1
	s.Store(new Article() {Text = "Ipsum lorem ipsum is simply text. Lorem Ipsum."}); // articles/2
	s.Store(new Article() {Text = "Lorem ipsum. Ipsum is simply text."}); // articles/3

In order to sort by Lucene score value use OrderByScore extension method (import Raven.Client namespace). To see the score calculated by Lucene get the document metadata in the same session scope as the executed query and take Temp-Index-Score key.

using (var session = store.OpenSession())
	var articles = session.Query<Article>("Articles/ByText")
						  .Customize(x => x.WaitForNonStaleResults())
						  .Where(x => x.Text == "ipsum")

	var articlesWithLuceneScore = articles.Select(x =>
			Score = session.Advanced.GetMetadataFor(x).Value<double>("Temp-Index-Score"),

The articles in the sample code above will be returned in the following order:

	Id = "articles/2", 
	Text = "Ipsum lorem ipsum is simply text. Lorem Ipsum.", 
	Score = 1.2337708473205566 
	Id = "articles/3",
	Text = "Lorem ipsum. Ipsum is simply text.", 
	Score = 1.0073696374893188 
	Id = "articles/1", 
	Text = "Lorem ipsum is simply text.", 
	Score = 0.712317943572998 

Note that the more times the word ipsum appears in the article the higher Score factor the document has.