Querying: MoreLikeThis

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.

public class Article {
    private String id;
    private String name;
    private String articleBody;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getArticleBody() {
        return articleBody;
    }

    public void setArticleBody(String articleBody) {
        this.articleBody = articleBody;
    }
}

public class Articles_ByArticleBody extends AbstractIndexCreationTask {
    public Articles_ByArticleBody() {
        map = "from doc in docs.articles " +
            "select new {" +
            "   doc.articleBody " +
            "}";

        store("articleBody", FieldStorage.YES);
        analyze("articleBody", "StandardAnalyzer");
    }
}

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

List<Article> articles = session
    .query(Article.class, Articles_ByArticleBody.class)
    .moreLikeThis(builder -> builder.usingDocument(x -> x.whereEquals("id()", "articles/1")))
    .toList();

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.

MoreLikeThisOptions options = new MoreLikeThisOptions();
options.setFields(new String[]{ "articleBody" });
List<Article> articles = session
    .query(Article.class, Articles_ByArticleBody.class)
    .moreLikeThis(builder -> builder
        .usingDocument(x -> x.whereEquals("id()", "articles/1"))
        .withOptions(options))
    .toList();

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.

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:

MoreLikeThisStopWords stopWords = new MoreLikeThisStopWords();
stopWords.setStopWords(Arrays.asList("I", "A", "Be"));
session.store(stopWords, "Config/Stopwords");

The document ID will then be set in the MoreLikeThisOptions.