Querying with Hibernate Search in Java

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Querying with Hibernate Search
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delayed the result page rendering in increments of 100 milliseconds and found that even small delays would result in a significant drop in revenue. There are several ways to speed up performance, and pagination is one of them. Of course, depending on the target user and the type of data, the pagination window needs to be adjusted.
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There s nothing worse for a user than to rely on a search engine and fail to receive an answer (well, maybe there are worse things, but you get the point). A key influence on user happiness is to have the search engine tuned to maximize the relevance of the results, especially the first few results. One way to achieve that is to study the kind of queries users enter and the kind of results they expect. From there, you can adjust the properties you search into, their boost factors and the kind of Lucene queries you use (fuzzy, range, and so on; see chapter 7 for more information).
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Let s explore the pagination API.
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The same pagination API used by HQL queries is used in full-text queries. You ve already seen this API in listing 6.13 while implementing the I m Feeling Lucky feature. Listing 6.14 shows a more traditional use of pagination to display partial results.
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Listing 6.14 Using pagination on a full-text query
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//Hibernate Core public List<String> displayAllByMatchingTitle( String words, int pageNumber, int window) { FullTextSession ftSession = SessionHolder.getFullTextSession(); org.apache.lucene.search.Query luceneQuery = buildLuceneQuery( words, Item.class ); org.hibernate.Query query = ftSession.createFullTextQuery( luceneQuery, Item.class ); @SuppressWarnings("unchecked") List<Item> items = query .setFirstResult( (pageNumber - 1) * window ) .setMaxResults( window ) .list();
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Set first result from the page
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Set number of results
List<String> results = new ArrayList<String>(); for (Item item : items) { StringBuilder itemInString = new StringBuilder( "Item " ) .append( "(" ).append( item.getEan() ).append( ")" )
Paginating through results and finding the total
.append( " " ).append( item.getTitle() ); results.add( itemInString.toString() ); } return results; }
//Java Persistence public List<String> displayAllByMatchingTitle(String words, int pageNumber, int window) { FullTextEntityManager ftEntityManager = EntityManagerHolder.getFullTextEntityManager(); org.apache.lucene.search.Query luceneQuery = buildLuceneQuery( words, Item.class ); javax.persistence.Query query = ftEntityManager.createFullTextQuery( luceneQuery, Item.class ); @SuppressWarnings("unchecked") List<Item> items = query .setFirstResult( (pageNumber - 1) * window ) .setMaxResults( window ) .getResultList();
Set pagination according to the window
List<String> results = new ArrayList<String>(); for (Item item : items) { StringBuilder itemInString = new StringBuilder( "Item " ) .append( "(" ).append( item.getEan() ) .append( ")" ) .append( " " ).append( item.getTitle() ); results.add( itemInString.toString() ); } return results; }
B Set the first element returned starting from index 0 (the first page starts at 0, the second at window 1, and so on). C Set the maximum number of results returned. D The same API is available from Java Persistence. Pagination limits the number of Lucene documents loaded as well as the number of objects hydrated. Because executing a Lucene query is quite cheap, you should execute the query a second time when a user wishes to see the next page rather than keeping the results around.
maxResults represents the maximum number of results returned and is usually the total number of results returned. However, if firstResult is close to the end of the list (less than maxResults away from the last index), the total number of results is lower than maxResults. If firstResult is beyond the end of the list, no result is returned. Make sure your pagination client code is aware of this behavior.
One of the traditional problems with pagination in SQL lies in the fact that you cannot find the total number of matching results unless a second query (select count(*) from ...) is performed.
Querying with Hibernate Search
Retrieving the total number of results
Full-text queries are completely different from SQL queries, and the total number of results is accessible without the extra SQL query cost. Hibernate Search exposes this information in the FullTextQuery API (see listing 6.15).
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