Hibernate Iterate throught Batches

hibernateBatch

//The query for the books:
//Reference : http://www.laliluna.de/articles/java-persistence-hibernate/performance-tips-hibernate-java-persistence.html
List<Book> books = session.createQuery( 
   “from Book b where b.name like ?”).setString(0, “Java%”).list(); 



/* The following code printing the books will create one SQL query per
book to initialize the chapters. We get 1+n queries in total. One for
the books and n for the chapters, if we have n books.
*/
for (Book book : books) { 
   int totalLength = 0; 
   for (Chapter chapter : book.getChapters()) { 
      totalLength += (chapter.getContent() != null ? 
      chapter.getContent().length() : 0); 
   } 
   log.info("Length of all chapters: " + totalLength); 
} 


//Solution

/* One way to improve this is to define
that Hibernate loads the chapters in batches. Here is the mapping:

Annotations
*/
OneToMany(cascade = CascadeType.ALL) <br>JoinColumn(nullable = false) 
@BatchSize(size = 4) 
private Set<Chapter> chapters = new HashSet<Chapter>(); 

//Also, the same can also be solved with CRITERIA QUERY
//The same with a criteria query:

List<Book> books = session.createCriteria(Book.class) 
   .setFetchMode(”chapters", org.hibernate.FetchMode.JOIN) 
   .add(Restrictions.like(“name”, “Java”, MatchMode.START)) 
   .setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY).list();