Emerging Technology Fall Semester, 2004 Joins & Many-to-One
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CS 683 Emerging Technologies Fall Semester, 2004 Doc 31 Joins & Many-to-One

Contents

References

Joins

Inner Join (or just Join)

Outer Join

Many-to-One Bidirectional

Classes

Tables

Mapings

Methods

Write, Update & Delete Cascading

Some Useful Session Methods

Logging – log4j

Copyright ©, All rights reserved. 2004 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA. OpenContent ( http://www.opencontent.org/opl.shtml) license defines the copyright on this document

References

Hibernate Reference 2.1.6

Online html version http://www.hibernate.org/hib_docs/reference/en/html/

Other versions (including Chinese) at: http://www.hibernate.org/5.html

Hibernate in Action, Bauer & King

Log4j Documentation, http://logging.apache.org/log4j/docs/

CS 683 Fall 04

Doc 31, Joins & Many-to-One Slide # 3

Joins

People

Email_Addresses

The tables have a column in common as email_addresses.person_id refers to people.id. So we can create a new table by joining the two tables together on that column

Inner Join (or just Join)

Only uses entries linked in two tables

select 
   first_name, last_name, user_name, host  
from 
   people, email_addresses 
where 
   people.id = email_addresses.person_id;

or equivalently

select 
   first_name, last_name, user_name, host  
from 
   people inner join email_addresses 
on 
   (people.id = email_addresses.person_id);

Outer Join

Uses all entries from a table

Left Outer Join

Use all entries from the left table

select 
   first_name, last_name, user_name, host  
from 
   people left outer join email_addresses 
on 
   (people.id = email_addresses.person_id);

Right Outer Join

Use all entries from the right table

select 
   first_name, last_name, user_name, host  
from 
   people right outer join email_addresses 
on 
   (people.id = email_addresses.person_id);

A right outer join B & B left outer join A

The following two statements are equivalent

select 
   first_name, last_name, user_name, host  
from 
   people right outer join email_addresses 
on 
   (people.id = email_addresses.person_id);

select 
   first_name, last_name, user_name, host  
from 
   email_addresses left outer join people
on 
   (people.id = email_addresses.person_id);

Many-to-One Bidirectional

Classes

public class Person {
   String firstName;
   String lastName;
   Set addresses;
   long id;

public class EmailAddress {
   String userName;
   String host;
   Person owner;
   long id;

Tables

People

Email_Addresses

CREATE TABLE PEOPLE (
   ID serial NOT NULL ,
   FIRST_NAME varchar(50) NULL ,
   LAST_NAME varchar(50) NULL , 
   CONSTRAINT PEOPLE_PK PRIMARY KEY  (id),
   CONSTRAINT PEOPLE_UNIQ UNIQUE  (id))
   
CREATE TABLE EMAIL_ADDRESSES (
   USER_NAME varchar(50) NULL ,
   HOST varchar(50) NULL ,
   ID serial NOT NULL ,
   PERSON_ID int4 NULL , 
   CONSTRAINT EMAIL_ADDRESSES_PK PRIMARY KEY  (id),
   CONSTRAINT EMAIL_ADDRESSES_UNIQ UNIQUE  (id))

Mapings

EmailAddress.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
   "-//Hibernate/Hibernate Mapping DTD//EN"
   "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd" >
   
<hibernate-mapping package="cs683">
   <class
      name="EmailAddress"
      table="EMAIL_ADDRESSES" >
         <id
         name="id"
         type="long"
         column="id">
         <generator class="increment"/>
      </id>
      <property
         name="userName"
         column="user_name"
         type="string"
         not-null="false"
         length="50"/>
      <property
         name="host"
         column="host"
         type="string"
         not-null="false"
         length="50" />
   <many-to-one name="owner" column="person_id" class="Person" not-null="true">
   </many-to-one>
   </class>
</hibernate-mapping>

Person.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
   "-//Hibernate/Hibernate Mapping DTD//EN"
   "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd" >
   
<hibernate-mapping package="cs683">
   <class
      name="Person"
      table="people"
   >
      <id
         name="id"
         type="long"
         column="id"
      >
         <generator class="increment"/>
      </id>
   
      <set name="addresses" 
               inverse="false" 
               cascade="all"
               table="EMAIL_ADDRESSES">
         <key  column="person-id"/>
   
         <one-to-many class="cs683.EmailAddress" />   
         
      </set>

Person.hbm.xml Continued

      <property
         name="lastName"
         column="last_name"
         type="string"
         not-null="false"
         length="50"
      />
      <property
         name="firstName"
         column="first_name"
         type="string"
         not-null="false"
         length="50"
      />
   
   </class>
</hibernate-mapping>

No changes from Document 30

Methods

Write

   static void sampleWrite() throws MappingException, HibernateException,
         Exception
      {
      Session session = getHibernateSession();
      Transaction save = null;
      try
         {
         save = session.beginTransaction();
         Person newPerson = new Person("Susan", "Many");
   
         EmailAddress bar = new EmailAddress("foo", "bar.aol.com");
         EmailAddress cat = new EmailAddress("catwoman", "gmail.com");
         newPerson.addAddress(cat);
         newPerson.addAddress(bar);
         session.save(bar);
         session.save(cat);
         session.save(newPerson);
         save.commit();
         }
      catch (Exception problem)
         {
         if (save != null)
            save.rollback();
         throw problem;
         }
      finally
         {
         session.close();
         }
      }

Set all the links before saving

Read

   static void sampleRead() throws MappingException, HibernateException,
         Exception
      {
      String query = "select p from Person p join p.addresses address where 
                  address.host like '%gmail%'"
      Session session = getHibernateSession();
      Query getGmailUser = 
      session.createQuery(query);
      List result = getGmailUser.list();
      System.out.println("Number of People: " + result.size());
   
      Object first =result.get(0);
      System.out.println( first);
      session.close();
      }

Select

Select indicates which type of object to return

select 
   address 
from 
   Person p join p.addresses address 
where 
   address host like ‘%gmail%’
   
select 
   p 
from 
   Person p join p.addresses address 
where 
   address host like ‘%gmail%’

Select without a Join

select p from Person p where p.lastName = 'Beck’

Joins

Hibernate supports

• Inner join
• Left outer join
• Right outer join

Inner join

Join defaults to inner

The following are equivalent

select 
   p 
from 
   Person p join p.addresses address
   
select 
   p 
from 
   Person p inner join p.addresses address

Outer Joins

The left join will get Eckberg

select 
   p 
from 
   Person p left join p.addresses address 
where 
   address host like ‘%gmail%’ or p.lastName like ‘E%’

The right join will not get Eckberg

select 
   p 
from 
   Person p right join p.addresses address 
where 
   address host like ‘%gmail%’ or p.lastName like ‘E%’

People

Email_Addresses

Selecting Multiple Objects

select p, address from Person p join p.addresses address

Session session = getHibernateSession();
Query getGmailUser = session
      .createQuery("select p, address from Person p join p.addresses address");
   
List result = getGmailUser.list();
System.out.println("Number of People: " + result.size());
   
for (int k = 0; k < result.size(); k++)
   {
   Object[] resultArray = (Object[]) result.get(k);
   Person personResult = (Person) resultArray[0];
   EmailAddress addressResult = (EmailAddress) resultArray[1];
   System.out.println("" + personResult + " " + addressResult);
   }
   
session.close();

Update

   static void sampleUpdate() throws MappingException, HibernateException,
         Exception
      {
      Session session = getHibernateSession();
      Transaction update = session.beginTransaction();
      Query getGmailUser = session.createQuery( 
         "select p from Person p join p.addresses address where 
         address.host='gmail.com'") ;
   
      List result = getGmailUser.list();
      Person gmailUser = (Person) result.get(0);
   
      gmailUser.setFirstName("Roger");
      Iterator listEmails =  gmailUser.getAddresses().iterator();
      while (listEmails.hasNext())
         {
         EmailAddress anAddress =(EmailAddress) listEmails.next();
         if (anAddress.getHost().equals("gmail.com"))
            anAddress.setHost("gmail.google.com");
         }
      update.commit();
      session.close();
      }

Delete

   static void sampleDelete() throws MappingException, HibernateException,
         Exception
      {
      Session session = getHibernateSession();
      Transaction deleter = null;
      try
         {
         deleter = session.beginTransaction();
         Query getGmailUser = session.createQuery(
            "select p from Person p join p.addresses address where 
               address.host like '%gmail%'");
         Person result = (Person) getGmailUser.uniqueResult();
         session.delete(result);
         deleter.commit();
         }
      catch (Exception problem)
         {
         if (deleter != null) deleter.rollback();
         throw problem;
         }
      finally
         {
         session.close();
         }
      }

Does this delete the email addresses?

Write, Update & Delete Cascading

<set 
      name="addresses" 
      inverse="false" 
      cascade="all" 
      table="EMAIL_ADDRESSES">
   <key  column="person_id"/>
   <one-to-many class="cs683.EmailAddress" />
</set>

Values for Cascade

all – cascade write, update & delete

none – no cascading

save-update – cascade only update & save

delete – cascade only deletes

Some Useful Session Methods

Hibernate API http://www.hibernate.org/hib_docs/api/

Session API http://www.hibernate.org/hib_docs/api/net/sf/hibernate/Session.html

int delete(String query) throws HibernateException

Delete all objects returned by the query

public Iterator iterate(String query) throws HibernateException

Execute a query and return the results in an iterator.

public void saveOrUpdate(Object object)

throws HibernateException

Either save() or update() the given instance, depending upon the value of its identifier property

Logging – log4j

Main Web site http://logging.apache.org/log4j/docs/

Defines 5 levels of logging (from weak to strong)

• Debug
• Info
• Warn
• Error
• Fatal

Logging methods

• void debug(Object message)
• void debug(Object message, Throwable t)
• void info(Object message)
• void info(Object message, Throwable t)
• void warn(Object message)
• void warn(Object message, Throwable t)
• void error(Object message)
• void error(Object message, Throwable t)
• void fatal(Object message)
• void fatal(Object message, Throwable t)

Can set

• Which level of log messages are recorded
• Where log message is recoded
• Normally done in configuration file

DEBUG < INFO < WARN < ERROR < FATAL

Example

import org.apache.log4j.Logger;
   
public class Foo
   {
   static Logger log = Logger.getLogger(Foo.class);
   
   public static void main(String[] args) throws Exception
      {
      log.info("Starting Foo.main" + Foo.class);
      new Foo().sampleMethod();
      log.info("End Foo.main");
      }
   
   public void sampleMethod() throws Exception
      {
      int x =0;
      int y = 1;
      try
         {
         int z = y/x;
         }
      catch (Exception e)
         {
         log.fatal("In Sample",e);
         throw e;
         }
      }
   }

Configuration File - log4j.properties

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n
   
log4j.rootLogger=off, stdout
log4j.logger.cs683=error

log4j.properties file placed in a directory in the classpath

Can read file manually

Set log levels per package

Loggers inherit values from parent logger

RootLogger is ancestor of all loggers

Order of logging levels

ALL < DEBUG < INFO < WARN < ERROR < FATAL < OFF

Hibernate log4j.properties

### direct log messages to stdout ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n
   
### direct messages to file hibernate.log ###
#log4j.appender.file=org.apache.log4j.FileAppender
#log4j.appender.file.File=hibernate.log
#log4j.appender.file.layout=org.apache.log4j.PatternLayout
#log4j.appender.file.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n
   
### set log levels - for more verbose logging change 'info' to 'debug' ###
   
log4j.rootLogger=off, stdout
   
log4j.logger.net.sf.hibernate=off
   
### log just the SQL
log4j.logger.net.sf.hibernate.SQL=debug
   
### log JDBC bind parameters ###
log4j.logger.net.sf.hibernate.type=off
   
### log schema export/update ###
log4j.logger.net.sf.hibernate.tool.hbm2ddl=debug
   
### log cache activity ###
#log4j.logger.net.sf.hibernate.cache=debug

Handling Errors

static void sampleDelete() throws MappingException, HibernateException,
      Exception
   {
   log.debug("Enter delete");
   Session session = getHibernateSession();
   Transaction deleter = null;
   try
      {
      deleter = session.beginTransaction();
      session.delete("select p from Person p join p.addresses address 
            where address.host like '%gmail%'");
      deleter.commit();
      }
   catch (Exception problem)
      {
      if (deleter != null)
         deleter.rollback();
      log.error("Delete problem", problem);
      throw problem;
      }
   finally
      {
      session.close();
      }
   log.debug("Exit delete");
   }

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