2d barcode vb.net Understanding the query paradigm in Java

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Understanding the query paradigm
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overall application. In lieu of manipulating (managed) objects from your domain model all the way up to your presentation layer, you ll need to deal with native Lucene API objects and play by their lifecycle. This could mean a significant API and programmatic shift in your application, and you d lose the benefits of object-oriented design, such as type-safety and strong typing. Hibernate Search relieves you of this burden. As you ve just seen, working manually with Lucene to execute the query and process the elements has some challenges. This chapter will show you how Hibernate Search makes this process much simpler for the application developer.
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Query mimicry
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Ideally, creating and invoking a full-text query should be no different than creating and invoking an HQL query. The APIs and the process should be similar enough for the application developer to feel at home. This is exactly the goal Hibernate Search tries to achieve. Queries run by Hibernate Search are similar to queries created in HQL, JPA-QL, or the Criteria API (Hibernate Criteria query API) in many ways:
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Returned objects are Hibernate managed objects. The query API is similar. The query semantic is also similar.
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Objects returned by a Hibernate Search full-text query are regular Hibernate managed objects attached to a persistence context. You can:
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Navigate from them and benefit from the transparent lazy-loading mechanism. Change the state of these objects; the change will be propagated to the database (and the index).
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As a matter of fact, a JPA-QL query and a full-text query that retrieve the same set of objects will return the same object instances (in a given Hibernate Session or Java Persistence EntityManager). Listing 6.1 shows the mimicry in action. Queries returning the same objects will benefit from the persistence context unicity regardless of the query mechanism.
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Listing 6.1 Mimicry in action Look up an object
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Item itemFromGet = (Item) session.get( Item.class, id ); Criteria criteriaQuery = session.createCriteria( Item.class ) .add( Restrictions.idEq( id ) ); Item itemFromCriteria = (Item) criteriaQuery.uniqueResult();
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TermQuery termQuery = new TermQuery( new Term( "id", id.toString() ) ); Item itemFromFullText = (Item) session Load through .createFullTextQuery( termQuery, Item.class ) the Criteria API .uniqueResult(); Load through a full-
text query assert itemFromGet == itemFromCriteria; assert itemFromCriteria == itemFromFullText;
assert itemFromGet == itemFromFullText;
All object references are the same
Querying with Hibernate Search
Since objects returned by a full-text search are retrieved from the persistence context, interacting with them in the rest of the application is completely transparent. They are treated as any object retrieved by Hibernate (HQL, Criteria query, lookup, or full-text). Hibernate Search pushes the similarity even further by sharing the same query interface as the other Hibernate query facilities. The object returned by the full-text query build method (FullTextSession.createFullTextQuery()) implements either org.hibernate.Query or javax.persistence.Query. Once the query object is created, using it is exactly the same as using a traditional HQL query (execution, pagination, and so on). Now that you re aware of the semantics, let s see how Hibernate Search converts a Lucene query into Hibernate objects.
Getting domain objects from a Lucene query
Let s assume that you have a Lucene Query object ready to be executed (see chapter 7 for more information). Instead of manually opening a Lucene Index Reader object and calling the search method, you pass the raw Lucene Query object to Hibernate Search. Hibernate Search applies its magic sauce to the Lucene query: Some ingredients are put in before execution, but most after. The query execution logic is displayed in figure 6.1. Hibernate Search prepares the Lucene query before its execution:
It determines the Lucene Directorys and opens the correct IndexReaders based on the targeted classes (generally, Hibernate Search will reuse IndexReader instances instead of physically opening them for each query). It sets the optional sort criteria (sorting is described in section 6.7). It applies the optional declarative filters (chapter 8 covers this topic).
The Lucene query is then executed. At this stage, by executing the Lucene query and without having to load any object or document, we know the total number of objects matching the query. In the next step, Hibernate Search reads the necessary matching Lucene Documents. Depending on the execution choice (list(), iterate(), scroll()) and the
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