cs 157b: database management systems ii january 30 class meeting department of computer science san...

CS 157B: Database Management Systems IIJanuary 30 Class Meeting

Department of Computer ScienceSan Jose State University

Spring 2013Instructor: Ron Mak

www.cs.sjsu.edu/~mak

Department of Computer ScienceSpring 2013: January 30

CS 157B: Database Management Systems II© R. Mak

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Form Project Teams

3 students each. Pick a team name.

Each team member will get the same score for each team project.

Teams will last the entire semester. Choose your team members wisely!

Someone from each team send me: Your team name Name and email address of each team member

If necessary, I will arbitrarily form teams by randomly assigning students.



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Project #1

At this time, each team should: Find an interesting dataset to download.

Or make up a dataset.

Design tables with one-to-one, one-to-many, and many-to-many associations. Add new tables (and populate with sample data)

as necessary.

Design an application with queries that will show off your tables and their associations. Such as by printing reports.

Start thinking about how to use Hibernate!



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Hibernate on NetBeans and Eclipse

See my write-up:

http://www.cs.sjsu.edu/~mak/CS157B/projects/1/Hibernate.pdf



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Student.java

@Entitypublic class Student { private long id; private String firstName; private String lastName; public Student() {} public Student(String firstName, String lastName) { this.firstName = firstName; this.lastName = lastName; } ...}



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Student.java

@Entitypublic class Student { ... @Id @GeneratedValue @Column(name="id") public long getId() { return id; } public void setId(long id) { this.id = id; } @Column(name="first_name") public String getFirstName() { return firstName; } public void setFirstName(String name) { this.firstName = name; } @Column(name="last_name") public String getLastName() { return lastName; } public void setLastName(String name) { this.lastName = name; } ...}



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Student.java

Main method (for testing)

public static void main(String args[]){ // Configure Hibernate and add the Student class. AnnotationConfiguration config = new AnnotationConfiguration(); config.addAnnotatedClass(Student.class); config.configure(); // Create the database table. (new SchemaExport(config)).create(true, true); // Create a session. SessionFactory factory = config.buildSessionFactory(); Session session = factory.openSession(); ...}



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Student.javapublic static void main(String args[]){ ... // Create a session. SessionFactory factory = config.buildSessionFactory(); Session session = factory.openSession(); // Load the Student table in a transaction. Transaction tx = session.beginTransaction(); { session.save(new Student("Mary", "Jane")); session.save(new Student("Kim", "Smith")); session.save(new Student("John", "Doe")); session.save(new Student("Tim", "Novak")); session.save(new Student("Leslie", "Klein")); } tx.commit(); session.close();}

SchoolDemo1



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HibernateContext.java

Goal: Move all the Hibernate bookkeeping code into a shared class.



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HibernateContext.javaimport org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.AnnotationConfiguration;import org.hibernate.tool.hbm2ddl.SchemaExport;

public class HibernateContext { public static AnnotationConfiguration config = null; public static SessionFactory factory = null; /** * Set the configuration if it is null. */ private static void setConfiguration() { if (config == null) { config = new AnnotationConfiguration(); config.configure(); } }

...}



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public class HibernateContext { public static AnnotationConfiguration config = null; public static SessionFactory factory = null;

... /** * Set the factory if it is null. */ private static void setFactory() { if (factory == null) { setConfiguration(); factory = config.buildSessionFactory(); } } ...}



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... /** * Open a session from the factory. * @return a session. */ public static Session getSession() { setFactory(); return factory.openSession(); } ...}



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... /** * Create a new schema (database) from the configuration. */ public static void createSchema() { setConfiguration(); (new SchemaExport(config)).create(true, true); } ...}



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... /** * Add a new class object to the database. * @param klass the class object. */ public static void addClass(Class klass) { setConfiguration(); config.addAnnotatedClass(klass); } ...}



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... /** * Add a list of class objects to the database. * @param klasses the list of class objects. */ public static void addClasses(Class klasses[]) { for (Class klass : klasses) { addClass(klass); } }}



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Student.java@Entitypublic class Student { ...

public static Student find(long id) { Session session = HibernateContext.getSession(); Query query = session.createQuery("from Student where id = :idvar"); query.setLong("idvar", id); Student student = (Student) query.uniqueResult(); session.close(); return student; }

...}

Hibernate Query Language (HQL)



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Student.java@Entitypublic class Student { ...

public static Student find(String lastName) { Session session = HibernateContext.getSession(); Query query = session.createQuery("from Student where lastName = :name"); query.setString("name", lastName); Student student = (Student) query.uniqueResult(); session.close(); return student; }

...}



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Teacher.java

Similar to Student.java

@Entitypublic class Teacher { private long id; private String firstName; private String lastName; public Teacher () {} public Teacher(String firstName, String lastName) { this.firstName = firstName; this.lastName = lastName; } ...}



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Teacher.java

@Entitypublic class Teacher { ... @Id @GeneratedValue @Column(name="id") public long getId() { return id; } public void setId(long id) { this.id = id; } @Column(name="first_name") public String getFirstName() { return firstName; } public void setFirstName(String name) { this.firstName = name; } @Column(name="last_name") public String getLastName() { return lastName; } public void setLastName(String name) { this.lastName = name; } ...}



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Teacher.java@Entitypublic class Teacher { ... /** * Load the Teacher table. */ public static void load() { Session session = HibernateContext.getSession(); Transaction tx = session.beginTransaction(); { session.save(new Teacher("Tom", "Rogers")); session.save(new Teacher("Art", "Thompson")); session.save(new Teacher("John", "Lane")); session.save(new Teacher("Mabel", "Flynn")); } tx.commit(); session.close(); System.out.println("Teacher table loaded."); } ...}



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Teacher.java

@Entitypublic class Teacher { ... /** * List all the teachers. */ public static void list() { Session session = HibernateContext.getSession(); Query query = session.createQuery("from Teacher"); System.out.println("All teachers:"); for (Teacher teacher : (List<Teacher>) query.list()) { teacher.print(); } session.close(); }}



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Teacher.java

@Entitypublic class Teacher { ... /** * Print teacher attributes. */ public void print() { System.out.printf("%d: %s %s\n", id, firstName, lastName); } ...}



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SchoolDemo.javaimport java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;

public class SchoolDemo { private static final String HELP_MESSAGE = "*** Commands: create, load, find <n>, students, teachers, quit"; public static void main(String args[]) { BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in)); String command; Class klasses[] = {Student.class, Teacher.class}; HibernateContext.addClasses(klasses);

... }}



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SchoolDemo.javapublic class SchoolDemo { ... public static void main(String args[]) { ... do { System.out.print("\nCommand? "); try { command = stdin.readLine(); } catch (java.io.IOException ex) { command = "?"; } String parts[] = command.split(" ");

... } while (!command.equalsIgnoreCase("quit")); }}



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SchoolDemo.javapublic class SchoolDemo { ... public static void main(String args[]) { ...

do { ... if (command.equalsIgnoreCase("create")) { HibernateContext.createSchema(); } else if (command.equalsIgnoreCase("load")) { Student.load(); Teacher.load(); }




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SchoolDemo.javapublic class SchoolDemo { ... public static void main(String args[]) { ...

do { ...

else if (command.equalsIgnoreCase("teachers")) { Teacher.list(); } else if (command.equalsIgnoreCase("students")) { Student.list(); }




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SchoolDemo.javapublic class SchoolDemo { ... public static void main(String args[]) { ... do { ... else if (parts[0].equalsIgnoreCase("find") && (parts.length >= 2)) { long id = Long.parseLong(parts[1]); Student student = Student.find(id); if (student != null) { student.print(); } else { System.out.printf("*** No student with id %d\n", id); } } ... } while (!command.equalsIgnoreCase("quit")); }}

SchoolDemo2



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One-to-One Association

Recall:

Id Last First Contact_id

7003 Rogers Tom 207

7008 Thompson Art 190

7012 Lane John 458

7051 Flynn Mabel 856

Id Email_address

458 [email protected]




Teacher Contact_Info

Student Contact_Info

Also:



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ContactInfo.java@Entity@Table(name="Contact_Info")public class ContactInfo { private long id; private String emailAddress; public ContactInfo() {} public ContactInfo(String address) { this.emailAddress = address; } @Id @GeneratedValue @Column(name="id") public long getId() { return id; } public void setId(long id) { this.id = id; }

@Column(name="email_address") public String getEmailAddress() { return emailAddress; } public void setEmailAddress(String address) { this.emailAddress = address; }}



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Student.java (One-to-One)

@Entitypublic class Student { ...

private ContactInfo contactInfo; @OneToOne(cascade=CascadeType.ALL, fetch=FetchType.LAZY) @JoinColumn(name="contact_id") public ContactInfo getContactInfo() { return contactInfo; } public void setContactInfo(ContactInfo info) { this.contactInfo = info; }

...}



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Student.java (One-to-One)

@Entitypublic class Student { ...

public static void load() { Session session = HibernateContext.getSession(); // Load the Student table in a transaction. Transaction tx = session.beginTransaction(); { session.save(new Student("Mary", "Jane", new ContactInfo("[email protected]"))); session.save(new Student("Kim", "Smith", new ContactInfo("[email protected]"))); session.save(new Student("John", "Doe", new ContactInfo("[email protected]"))); session.save(new Student("Tim", "Novak", new ContactInfo("[email protected]"))); session.save(new Student("Leslie", "Klein", new ContactInfo("[email protected]"))); } tx.commit(); session.close();

System.out.println("Student table loaded."); }

...}



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Student.java (One-to-One)@Entitypublic class Student { ...

private ContactInfo contactInfo; ...

public void print() { System.out.printf("%d: %s %s (%s)\n", id, firstName, lastName, contactInfo.getEmailAddress()); }

...}



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Lazy Fetching

Each Student object has a one-to-one association with a ContactInfo object via its contactInfo field.

Whenever our Java program fetches a record from the Student table, Hibernate does not fetch the associated record from the Contact_Info table until our program references any field of the ContactInfo object. This is a Hibernate performance optimization.

private ContactInfo contactInfo;...@OneToOne(cascade=CascadeType.ALL, fetch=FetchType.LAZY)@JoinColumn(name="contact_id")public ContactInfo getContactInfo() { return contactInfo; }public void setContactInfo(ContactInfo info) { this.contactInfo = info; }

SchoolDemo3



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Lazy Initialization Exception

Hibernate throws the dreaded LazyInitializationException whenever your program attempts to access the field of an object whose corresponding table record has not yet been fetched, often due to lazy fetching.

In SchoolDemo3, we attempted to print the value of field emailAddress of a ContactInfo object.

The corresponding record had not yet been fetched from the Contact_Info table.

Hibernate can fetch table records only within the context of a session.



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Recall that after we fetched a matching record from the Student table, we closed the session.

Therefore, Hibernate couldn’t fetch the associated Contact_Info record, and we got the exception when we attempted to print the emailAddress field of the ContactInfo object.

public static Student find(long id){ Session session = HibernateContext.getSession(); Query query = session.createQuery("from Student where id = :idvar"); query.setLong("idvar", id); Student student = (Student) query.uniqueResult(); session.close(); return student;}



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One solution: Use eager fetching. Whenever Hibernate fetches a table record, it

immediately fetches records from associated tables.

private ContactInfo contactInfo;...@OneToOne(cascade=CascadeType.ALL, fetch=FetchType.EAGER)@JoinColumn(name="contact_id")public ContactInfo getContactInfo() { return contactInfo; }public void setContactInfo(ContactInfo info) { this.contactInfo = info; }

SchoolDemo3



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Lazy Initialization Exception However, eager fetching is not always a good idea.

Don’t defeat Hibernate’s performance optimization, especially if there are many associations and you’re fetching many records!

Better: Keep lazy fetching. Attach the Student object to another Hibernate session. Inside of this session, Hibernate can fetch the corresponding

Context_Info record to allow you to print ContactInfo fields.

public void printInSession(){ Session session = HibernateContext.getSession(); session.update(this); print(); session.close();}

Student.java

SchoolDemo3

cs 157b: database management systems ii january 30 class meeting department of computer science san...

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