Querying: moreLikeThis

  • moreLikeThis returns a list of documents that are related to a given document.
  • This feature can be used, for example, to show a list of related articles at the bottom of the currently-read article page, as done in many news sites.
  • To accomplish this, RavenDB uses the Lucene contrib project moreLikeThis feature.

  • In this page:


To be able to work, MoreLikeThis requires access to the index text.
The queried index needs, therefore, to store the fields or the term vectors for these fields.

class Article {
    constructor(id, name, articleBody) {
        this.id = id;
        this.name = name;
        this.articleBody = articleBody;

class Articles_ByArticleBody extends AbstractIndexCreationTask {
    constructor() {

        this.map = `from doc in docs.Articles select new { 

        this.store("articleBody", "Yes");
        this.analyze("articleBody", "StandardAnalyzer");

Basic Usage

Many MoreLikeThis options are set by default.
The simplest mode will satisfy most usage scenarios.

const articles = await session
    .query({ indexName: "Articles/ByArticleBody" })
    .moreLikeThis(builder => 
        builder.usingDocument(x => 
            x.whereEquals("id()", "articles/1")))
from index 'Articles/ByArticleBody' 
where morelikethis(id() = 'articles/1')

MoreLikeThis will use all the fields defined in an index.
To use only specific fields, pass these fields in the MoreLikeThisOptions.fields property.

const options = {
    fields: [ "articleBody" ]
const articles = await session
    .query({ indexName: "Articles/ByArticleBody" })
    .moreLikeThis(builder => builder
        .usingDocument(x => x.whereEquals("id()", "articles/1"))
from index 'Articles/ByArticleBody' 
where morelikethis(id() = 'articles/1', '{ "Fields" : [ "articleBody" ] }')


Default parameters can be changed by manipulating MoreLikeThisOptions properties and passing them to MoreLikeThis.

minimumTermFrequency number Ignores terms with less than this frequency in the source doc
maximumQueryTerms number Returns a query with no more than this many terms
maximumNumberOfTokensParsed number The maximum number of tokens to parse in each example doc field that is not stored with TermVector support
minimumWordLength number Ignores words less than this length or, if 0, then this has no effect
maximumWordLength number Ignores words greater than this length or if 0 then this has no effect
minimumDocumentFrequency number Ignores words which do not occur in at least this many documents
maximumDocumentFrequency number Ignores words which occur in more than this many documents
maximumDocumentFrequencyPercentage number Ignores words which occur in more than this percentage of documents
boost boolean Boost terms in query based on score
boostFactor number Boost factor when boosting based on score
stopWordsDocumentId string Document ID containing custom stop words
fields string[] Fields to compare

Stop Words

Some Lucene analyzers have a built-in list of common English words that are usually not useful for searching, like "a", "as", "the", etc.
These words, called stop words, are considered uninteresting and are ignored.
If a used analyzer does not support stop words, or you need to overload these terms, you can specify your own set of stop words.
A document with a list of stop words can be stored in RavenDB by storing the MoreLikeThisStopWords document:

const stopWords = new MoreLikeThisStopWords();
stopWords.stopWords = [ "I", "A", "Be" ];
await session.store(stopWords, "Config/Stopwords");

The document ID will then be set in the MoreLikeThisOptions.

{PANEL: Remarks}

Please note that default values for settings, like minimumDocumentFrequency, minimumTermFrequency, and minimumWordLength, may result in filtering out related articles, especially with a small data set (e.g. during development).