Robert Greiner CSE7330 Southern Methodist University Getting Things Done with Hibernate

Introduction – A quick Quiz.  How many of you are proficient in:

Quiz Results: How did you do?  Did you answer “Yes” to all of the databases?  If not, this presentation is for You!

Hibernate’s Most Important Features  Object to Relational Mapping Tool.  Relational databases do not map well to the real world  Takes Java Objects and maps them to relational tables Not easy!  Works with any relational database  Handles Database Transactions Automatically  Possible through mapping files  Programmers don’t need to worry about writing SQL FACT: Programmers are not typically proficient in SQL but still need to interact with databases on a regular basis.  Another tool to help you get things done.  Because that’s what gets you hired and keeps you employed

What Hibernate Isn’t?  The answer to all of your database problems.  No amount of awesome code will substitute for good design.  At the end of the day, data is stored in a relational model

Example  Suppose you have a system that needs to keep track of students and courses (easy)  Students Table  Courses Table  How do we express the m:n relationship for students that need to enroll in several courses? (not as easy)  Enrolled Table (This does not map well to an object)  Can Hibernate help with this?  Yes!

Let’s see some code

The Anatomy of a Hibernate Project  Java Classes  Student.java  Course.java  Hibernate Mapping File  Student.hbm.xml  Course.hbm.xml  Hibernate Files  hibernate.cfg.xml  HibernateUtil.java  StudentManager.java main() Regular Java Objects

Student.java public class Student { private long sid; private String firstName; private String lastName; private double gpa; Student() {} //Default constructor public Student(String firstName, String lastName, double gpa) { this.firstName = firstName; this.lastName = lastName; this.gpa = gpa; } public void setSid(long sid) { this.sid = sid; } public long getSid() { return this.sid; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; }... } Just a regular everyday Java class Need a getter/setter for each database value

Course.java public class Course { long cid; String name; Set students = new HashSet(); public Course() {} public Course(String name) { this.name = name; }... public String getName() { return name; } public void setName(String name) { this.name = name; } public Set getStudents() { return students; } public void setStudents(Set students) { this.students = students; } public void addStudent(Student student) { this.students.add(student); } Each course object holds a collection of the Students enrolled in it.

Student.hbm.xml Teach Hibernate how to map objects to the database <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN" "

Course.hbm.xml <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN" "

Hibernate.cfg.xml <!DOCTYPE hibernate-configuration SYSTEM " org.hsqldb.jdbcDriver jdbc:hsqldb:hsql://localhost sa org.hibernate.dialect.HSQLDialect false true

HibernateUtil.java – The Setup public class HibernateUtil { private static final SessionFactory sessionFactory = buildSessionFactory(); private static Session session = HibernateUtil.getSessionFactory().openSession(); private static SessionFactory buildSessionFactory() { try { return new Configuration().configure().buildSessionFactory(); } catch (Throwable ex) { System.out.println("Exception!!!!"); throw new ExceptionInInitializerError(ex); } public static SessionFactory getSessionFactory() { return sessionFactory; }...

HibernateUtil.java – Insert Students/Courses public static void insertStudents(List students) { //Inserts a list of students into the database Session session = HibernateUtil.getSessionFactory().openSession(); Transaction tx = session.beginTransaction(); for (Student s : students) { Long sid = (Long) session.save(s); } tx.commit(); session.close(); } public static void insertCourses(List courses) { Session session = HibernateUtil.getSessionFactory().openSession(); Transaction tx = session.beginTransaction(); for (Course c : courses) { Long sid = (Long) session.save(c); } tx.commit(); session.close(); }

HibernateUtil.java – Read Students/Courses private static List getStudents() { List students = new ArrayList (); students = session.createCriteria(Student.class).list(); return students; } private static List getCourses() { List courses = new ArrayList (); courses = session.createCriteria(Course.class).list(); return courses; }

HibernateUtil.java – Print Collections public static void printDatabaseState() { List students = getStudents(); List courses = getCourses(); Set studentsInCourse = new HashSet(); for (Student s : students) { System.out.println(s.getSid() + " - " + s.getFirstName() + " " + s.getLastName()); } for (Course c : courses) { studentsInCourse = c.getStudents(); System.out.println(c.getName()); for (Object s : studentsInCourse) { System.out.println(" " + ((Student)s).getFirstName() + " " + ((Student)s).getLastName()); }

StudentManager.java public class StudentManager { List students = new ArrayList (); List courses = new ArrayList (); public static void main(String[] args) { //Initialize and call each method } public void addStudents() { this.students.add(new Student("Albert", "Einstein", 4.0)); this.students.add(new Student("Carl", "Sagan", 2.5)); this.students.add(new Student("Alan", "Turing", 4.0)); this.students.add(new Student("Ken", "Thompson", 4.0)); this.students.add(new Student("Bill", "Gates", 0.0)); this.students.add(new Student("Steve", "Jobs", 3.5)); HibernateUtil.insertStudents(this.students); } public void addCourses() { this.courses.add(new Course("CSE7330")); this.courses.add(new Course("CSE5330")); this.courses.add(new Course("CSE7314")); this.courses.add(new Course("CSE8313")); this.courses.get(0).addStudent(this.students.get(0)); this.courses.get(0).addStudent(this.students.get(1)); this.courses.get(0).addStudent(this.students.get(2)); this.courses.get(1).addStudent(this.students.get(3)); this.courses.get(1).addStudent(this.students.get(5)); this.courses.get(2).addStudent(this.students.get(0)); this.courses.get(2).addStudent(this.students.get(1)); this.courses.get(3).addStudent(this.students.get(2)); this.courses.get(3).addStudent(this.students.get(3)); this.courses.get(3).addStudent(this.students.get(5)); HibernateUtil.insertCourses(this.courses); }

Results Program Output 1 - Albert Einstein 2 - Carl Sagan 3 - Alan Turing 4 - Ken Thompson 5 - Bill Gates 6 - Steve Jobs CSE7330 Alan Turing Albert Einstein Carl Sagan CSE5330 Steve Jobs Ken Thompson CSE7314 Albert Einstein Carl Sagan CSE8313 Alan Turing Steve Jobs Ken Thompson

Summary  It can be difficult to express real life objects as relations  Hibernate is an Object to Relational mapping tool  Example: No 3 rd Enrolled object needed Allows for a more Object Oriented approach  Hibernate allows you to interact with a database without having to know platform-specific SQL  Did you see one line of SQL in this presentation?

Future Applications  Web frameworks are moving towards ORM.  Rails (Ruby)  Django (Python)  Hibernate for other languages  nHibernate (.NET)

The 5 W’s of Hibernate  Who: Hibernate is maintained by Red Hat  What: Object to Relational Mapping Tool  When: Your next project that uses a database  Where: Project Homepage:  Why: Get things done!

References  Harnessing Hibernate  Dr. James Elliot  O'Reilly Media (April 1, 2008)  Amazon Link Amazon Link  Java Persistence with Hibernate  Christian Bauer  Manning Publications; Revised edition (November 24, 2006)  Amazon Link Amazon Link   Official Hibernate Project Site  Red Hat  11/11/2009   Hibernate Tutorials  Bushan Dongare  Good intro tutorial to hibernate  11/11/2009   Stack Overflow Tag for Hibernate Questions  Great community resource for getting your questions answered  Community Authored and Licensed 