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Building a Lucene query Query string
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String searchQuery = "title:Batman OR description:Batman"; QueryParser parser = new QueryParser( "title", new StandardAnalyzer() Analyzer ); used
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Build a query parser
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org.apache.lucene.search.Query luceneQuery; try { Build Lucene query luceneQuery = parser.parse(searchQuery); } catch (ParseException e) { throw new RuntimeException("Unable to parse query: " + searchQuery, e); }
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Once you ve expressed the query as a string representation, building a Lucene query with the query parser is a two-step process. The first step is to build a query parser, define the default field targeted in the query, and define the analyzer used during the query building. The default field is used when the targeted fields are not explicit in the query string. It turns out that the authors don t use this feature very often. Next we ll present a more interesting solution. Analyzers are a primary component of Lucene and a key to its flexibility. An analyzer is responsible for breaking sentences into individual words. We ll skip this notion for now and come back to it in greater detail in section 5.2, when you will be more familiar with Hibernate Search and Lucene. The query parser is now ready and can generate Lucene queries out of any syntax-compliant query string. Note that the query hasn t yet been executed. Lucene provides an improved query parser that allows you to target more than one field at a time automatically. Because Hibernate Search, by default, matches one property to one Lucene field, this query parser turns out to be very useful as a way to finely target which property to search by. Let s see how to use it (see listing 2.11).
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Getting started with Hibernate Search
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Listing 2.11
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Using the MultiFieldQueryParser Targeted fields Boost factors
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String searchQuery = "Batman"; String[] productFields = {"title", "description"};
Map<String,Float> boostPerField = new HashMap<String,Float>(2); boostPerField.put( "title", (float) 4); boostPerField.put( "description", (float) 1); QueryParser parser = new MultiFieldQueryParser( productFields, new StandardAnalyzer(), boostPerField );
Build multifield query parser
org.apache.lucene.search.Query luceneQuery; try { luceneQuery = parser.parse(searchQuery); } catch (ParseException e) { throw new RuntimeException("Unable to parse query: " + searchQuery, e); }
The MultiFieldQueryParser allows you to define more than one default field at a time. It becomes very easy to build queries that return all objects matching a given word or set of words in one or more object properties. In our example, the query will try to find Batman in either the title or the description field. The MultiFieldQueryParser also allows you to express the intuitive idea that title is more important than description in the query results. You can assign a different weight (also called boost factor) to each targeted field.
Building the Hibernate Search query
Our Lucene query is now ready to be executed. The next step is to wrap this query into a Hibernate Search query so that we can live in the full object-oriented paradigm. We already know how to retrieve a FullTextSession or FullTextEntityManager from a regular Session or EntityManager. A FullTextSession or a FullTextEntityManager is the entry point for creating a Hibernate Search query out of a Lucene query (see listing 2.12).
Listing 2.12 Creating a Hibernate Search query
FullTextSession ftSession = Search.getFullTextSession(session); org.hibernate.Query query = ftSession.createFullTextQuery( luceneQuery, Item.class); Return matching Items query = ftSession.createFullTextQuery( luceneQuery); Return all matching indexed entities query = ftSession.createFullTextQuery( luceneQuery, Item.class, Actor.class);
Return matching Items and Actors
Querying your data
FullTextEntityManager ftEm = Search.getFullTextEntityManager(entityManager); javax.persistence.Query query = ftEm.createFullTextQuery( luceneQuery, Item.class); javax.persistence.Query query = ftEm.createFullTextQuery( luceneQuery); javax.persistence.Query query = ftEm.createFullTextQuery( luceneQuery, Return matching Item.class, Items and Actors Actor.class);
Return matching Items Return all matching indexed entities
The query-creation method takes the Lucene query as its first parameter, which isn t really a surprise, but it also optionally takes the class targeted by the query as an additional parameter (see our first example). This method uses a Java 5 feature named varargs. After the mandatory Lucene query parameter, the method can accept any number of Class parameters (from zero to many). If no class is provided, the query will target all entities indexed. If one or more classes are provided, the query will be limited to these classes and their subclasses (Hibernate Search queries are polymorphic, just like Hibernate Query Language [HQL] queries). While most queries target one class, it can be handy in some situations to target more than one entity type and benefit from the unstructured capabilities of Lucene indexes. Note that by restricting the query to a few entity types (and especially one entity type), Hibernate Search can optimize query performance. This should be your preferred choice. The second interesting point to note is that the query objects are respectively of type org.hibernate.Query or javax.persistence.Query (depending whether you are targeting the Hibernate APIs or the Java Persistence APIs). This is very interesting because it enables a smooth integration with existing Hibernate applications. Anybody familiar with Hibernate or Java Persistence s queries will have no problem executing the query from this point.
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