Hibernate for Beginners


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Hibernate for Begginers

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Hibernate for Beginners

  1. 1. Hibernate Kick off
  2. 2. 1. 2. 3. 4. 5. 6. 7. Hibernate Introduction Why to use Hibernate Steps to use/configure hibernate in an application simple case study Transaction in Hibernate Using Criteria in Hibernate Caching in Hibernate
  3. 3. Hibernate Introduction: Hibernate is a powerful, high performance object/relational persistence and query service. Hibernate lets you develop persistent classes following objectoriented idiom - including association, inheritance, polymorphism, composition, and collections. Hibernate allows you to express queries in its own portable SQL extension (HQL), as well as in native SQL, or with an object-oriented Criteria and Example API.    Object/Relational Mapping Hibernate Dual-Layer Cache Architecture  Highly scalable architecture  J2EE integration  Object Relational tool ( JDO, Hibernate, and iBatis SQL Maps, TopLink)   Hibernate supports these following databases:
  4. 4. Why to use Hibernate In traditional approach: o Too many SQL statements o Manually handled associations o Database dependent
  5. 5. Hibernate architecture
  6. 6. Steps to use/configure hibernate in an application: A. Installing the Hibernate core and support JAR libraries into your project B. Creating a Hibernate.cfg.xml file to describe how to access your database C. Selecting appropriate SQL Dialect for the database. D. Creating individual mapping descriptor files for each persistable Java classes
  7. 7. Steps to use Hibernate A. Install the Hibernate core and JAR libraries
  8. 8. Steps to use Hibernate B. Creating a Hibernate.cfg.xml : Before Hibernate can retrieve and persist objects for us, we need to tell it the settings about our application. For example,     which kind of objects are persistent objects? Which kind of database are we using? How to connect to the database? What is the size of Connection pool? There are three ways to configure Hibernate in total: 1.      XML configuration 2.       programmatic configuration 3.       properties file configuration.
  9. 9. 9. Steps to use Hibernate XML Configuration
  10. 10. Steps to use Hibernate C. Selecting appropriate SQL Dialect for the database. The dialect property determines the dialect to be used when generating queries. Hibernate supports dialects for all popular Relational Database Management Systems (RDBMS), such as DB2 or Oracle™. Therefore, for example, if you use Oracle during development and want to move to DB2 in production, changes will only be required in the hibernate.cfg.xml file.
  11. 11. Steps to use Hibernate A.    Creating individual mapping/descriptor files for each persistable Java classes/Table in DB Table JAVA POJO Class XML HBM File RDBMS A
  12. 12. 12. Steps to use Hibernate A Table in Database       CREATE TABLE BOOK (    ISBN   VARCHAR(50) NOT NULL,    NAME VARCHAR(100) NOT NULL,    PRICE INT  NOT NULL,   PRIMARY KEY (ISBN)   );
  13. 13. Steps to use Hibernate Java (POJO):
  14. 14. Steps to use Hibernate Hibernate-mapping: (*.hbm.xml) 0
  15. 15. 4 simple case study
  16. 16. simple case study Creating global session factory: For an application using Hibernate as O/R mapping framework, a global session factory should be created and accessed through a particular interface. Here we use a static variable for storing the session factory. It is initialized in a static block when this class is loaded for the first time.
  17. 17. Simple Case Study Using the SessionFactory in Application:   SessionFactory factory = HibernateUtil.getSessionFactory();   Session session = factory.openSession();   try { } finally { //………………….. // Using the session to retrieve objects //………………………………. session.close(); } SessionFactorys are immutable. The behaviour of a SessionFactory is controlled by properties supplied at configuration time.
  18. 18. Simple Case Study Retrieving objects   Book book = (Book) session.load(Book.class, isbn); or Book book = (Book) session.get(Book.class, isbn);   What’s the difference between load() and get() ? The first difference is that when the given ID could not be found, load() will throw an exception “org.hibernate.ObjectNotFoundException”, while get() will return a null object. The second difference is that load() just returns a proxy by default and database won’t be hit until the proxy is first invoked. The get() will hit the database immediately.
  19. 19. 19. Simple Case Study Using HQL (Hibernate Query Language): If you are sure that there will be only one object matching, you can use the uniqueResult() method to retrieve the unique result object. So, the code would appear as:
  20. 20. 20. Simple Case Study persisting Objects:   For saving a newly created object, we can use the save() method. Hibernate will issue an INSERT statement.   session.save(book);   For updating an existing object, we can use the update() method. Hibernate will issue an UPDATE statement.   session.update(book);   For deleting an existing object, we can use the delete() method. Hibernate will issue a DELETE statement.   session.delete(book);
  21. 21. Id Generation in Hibernate
  22. 22. Simple Case Study ID generation in Hibernate   There are three approaches to set ID:   a. Sequence b. Identity c. Native
  23. 23. 23. Simple Case Study ID generation in Hibernate   There are three approaches to set ID:   a.Sequence To generate an ID is to use an auto-incremented sequence number. For some kinds of databases (including HSQLDB), we can use a sequence/generator to generate this sequence number:
  24. 24. Simple Case Study b. Identity: To generate an auto-incremented sequence number is to use an identity column of a table.
  25. 25. 25. Simple Case Study c. Native: most suitable strategy to use for your database
  26. 26. 26. Simple Case Study primary key generation using multiple columns: Table:
  27. 27. 27. Simple Case Study Java (POJO Class)
  28. 28. 28. Simple Case Study Mapping (an HBM file)
  29. 29. 5. Transaction in Hibernate:
  30. 30. Transaction in Hibernate:
  31. 31. 31. Transaction in Hibernate Example : select
  32. 32. 32. Transaction in Hibernate Example : update
  33. 33. Transaction in Hibernate Example : delete
  34. 34. 6 Using Criteria in Hibernate
  35. 35. 35. Transaction in Hibernate Sometimes we need to build up a query dynamically in our application, e.g. for an advanced search function.“Criteria Queries” is an alternative way of HQL query.The traditional method of doing this is to generate a HQL statement, or SQL statement if not using Hibernate, by string concatenation. The problem for this method is making your code hard to maintain because of the hard reading statement fragments. Traditinal approach: if (startDate != null) { if (firstClause) { query = query + " where "; } else { query = query + " and "; query += " s.date >= '" + startDate + "'"; } // And so on...
  36. 36. Transaction in Hibernate Hibernate Criteria: Criteria criteria = session.createCriteria(Book.class); if (startDate != null) { criteria.add(Expression.ge("date",startDate); } if (endDate != null) { criteria.add(Expression.le("date",endDate); } List results = criteria.list();
  37. 37. 37. Transaction in Hibernate SELECT * FROM ORDERS WHERE ORDER_ID=’1092’; In Cretira it would become: List orders= session.createCriteria(Order.class) .add(Restrictions.eq(“orderId”,”1092”)) .list(); SELECT O.*, P.* FROM ORDERS O, PRODUCT P WHERE O.ORDER_ID=P.ORDER_ID AND P.ID=’1111’; Would become List orders = session.createCriteria(Order.class) .setFetchMode(“products”,FetchMode.JOIN) .add(Restrictions.eq(“id”,”1111”)) .list();
  38. 38. 38. Transaction in Hibernate This criteria query corresponds to the following HQL query: from Book book where book.name = 'Hibernate for Beginners'
  39. 39. 39. Transaction in Hibernate •Restriction.between is used to apply a "between" constraint to the field. •Restriction.eq is used to apply an "equal" constraint to the field. •Restriction.ge is used to apply a "greater than or equal" constraint to the field. •Restriction.gt is used to apply a "greater than" constraint to the field. •Restriction.idEq is used to apply an "equal" constraint to the identifier property. •Restriction.in is used to apply an "in" constraint to the field. •Restriction.isNotNull is used to apply an "is not null" constraint to the field. •Restriction.isNull is used to apply an "is null" constraint to the field. •Restriction.ne is used to apply a "not equal" constraint to the field. IN: criteria.add(Restrictions.in("newCourseID", courseIDs));
  40. 40.   7. Caching in Hibernate:
  41. 41. 41. Caching in Hibernate Hibernate supports the caching of persistent objects at different levels: 1 st level of caching 2 nd Level of caching
  42. 42. 42. Caching in Hibernate 1. 1st level of caching:   Suppose we get an object with same identifier for two times within a session, will Hibernate query the database for two times? 
  43. 43. 43. Caching in Hibernate If we inspect the SQL statements executed by Hibernate, we will find that only one database query is made. That means Hibernate is caching our objects in the same session. This kind of caching is called “first level caching”, whose caching scope is a session.   But how about getting an object with same identifier for two times in two different sessions?
  44. 44. 44. Caching in Hibernate 2 nd Level of caching:
  45. 45. 45. Caching in Hibernate  We will find that two database queries are made. That means Hibernate is not caching the persistent objects across different sessions by default. We need to turn on this “second level caching” whose caching scope is a session factory.
  46. 46. 46 Caching in Hibernate To enable 2nd level of caching, update the ‘hibernate.cfg.xml’ To monitor the caching activities of Hibernate at runtime, we can add the following line to the log4j configuration file “log4j.properties”. log4j.logger.org.hibernate.cache=debug
  47. 47. Thank you.