Applying the same Analyzer to Queries and Fields - hibernate-search

Question

I am trying to build a basic search for my API backend. Users pass arbitrary queries and the backend is supposed to return results (obviously). I would prefer a solution that works with a local index as well as Elasticsearch.
On my entity I defined an analyzer like this:
#AnalyzerDef(name = "ngram",
tokenizer = #TokenizerDef(factory = StandardTokenizerFactory.class ),
filters = {
#TokenFilterDef(factory = StandardFilterFactory.class),
#TokenFilterDef(factory = LowerCaseFilterFactory.class),
#TokenFilterDef(factory = StopFilterFactory.class),
#TokenFilterDef(factory = NGramFilterFactory.class,
params = {
#Parameter(name = "minGramSize", value = "2"),
#Parameter(name = "maxGramSize", value = "3") } )
}
)
For the query, I tried the following:
FullTextEntityManager fullTextEntityManager = Search.getFullTextEntityManager(this.entityManager);
Analyzer analyzer = fullTextEntityManager.getSearchFactory().getAnalyzer("ngram");
QueryParser queryParser = new MultiFieldQueryParser(ALL_FIELDS, analyzer);
queryParser.setDefaultOperator(QueryParser.AND_OPERATOR);
org.apache.lucene.search.Query query = queryParser.parse(queryString);
javax.persistence.Query persistenceQuery =
fullTextEntityManager.createFullTextQuery(query, MyEntity.class);
List<MyEntity> result = persistenceQuery.getResultList();
As far as I understand, I need to provide an analyzer for the Query so that the search query are "ngram-tokenized" and a match can be found. Before, I used SimpleAnalyzer and as a result, the search only matched full words which - I think - backs my theory (Sorry, I am still learning this).
The above code gives me a NullPointerException:
java.lang.NullPointerException: null
at org.hibernate.search.engine.impl.ImmutableSearchFactory.getAnalyzer(ImmutableSearchFactory.java:370) ~[hibernate-search-engine-5.11.1.Final.jar:5.11.1.Final]
at org.hibernate.search.engine.impl.MutableSearchFactory.getAnalyzer(MutableSearchFactory.java:203) ~[hibernate-search-engine-5.11.1.Final.jar:5.11.1.Final]
at org.hibernate.search.impl.SearchFactoryImpl.getAnalyzer(SearchFactoryImpl.java:50) ~[hibernate-search-orm-5.11.1.Final.jar:5.11.1.Final]
in the line
Analyzer analyzer = fullTextEntityManager.getSearchFactory().getAnalyzer("ngram");

Answer 1

You cannot retrieve the analyzer from Hibernate Search when using the Elasticsearch integration, because in that case there is no analyzer locally: the analyzer only exists remotely, in the Elasticsearch cluster.
If you only need a subset of the query syntax, try out the "simple query string" query: it's a query that can be built using the DSL (so it will work the same with Lucene and Elasticsearch) and that provides the most common features (boolean queries, fuzziness, phrases, ...). For example:
Query luceneQuery = queryBuilder.simpleQueryString()
.onFields("name", "history", "description")
.matching("war + (peace | harmony)")
.createQuery();
The syntax is a bit different, but only because it's aiming at end users and tries to be simpler.
EDIT: If simple query strings are not an option, you can create an analyzer manually: this should work even when using the Elasticsearch integration.
org.apache.lucene.analysis.custom.CustomAnalyzer#builder() should be a good starting point. There are several examples in the javadoc of that class.
Make sure you only create the analyzer once and store it somewhere, e.g. in a static constant: creating an analyzer may be costly.