Emerging Technology Fall Semester, 2004 One-to-Many & HQL
	Previous     Lecture Notes Index     Next      © 2004, All Rights Reserved, SDSU & Roger Whitney San Diego State University -- This page last updated 22-Nov-04

CS 683 Emerging Technologies Fall Semester, 2004 Doc 30 One-to-Many & HQL

Contents

References

Many-to-One

Classes

Tables

Mapping Files

Some Mapping Options

Class

id

types

Generate Class

Property

Mapping Collections

Collection Mappings

Many-to-one

Variations

Queries - HQL

Querying a Class

Controlling Number of Hits

Getting One Result

Aliases

Restricting Queries

Logical Operators

Ordering Query Results

Properties of Properties

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

Many-to-One

Classes

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

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

Tables

People

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))

Mapping Files

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" />
   </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="save-update"
               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>

Some Mapping Options

Class

<class
   name="ClassName"
   table="tableName"
   
   mutable="true|false"         (default: true)
   dynamic-update="true|false"   (default: false)
   dynamic-insert="true|false"   (default: false)
   where="arbitrary sql where condition" 
   batch-size="N"
   lazy="true|false" 
/>

http://www.hibernate.org/hib_docs/reference/en/html/mapping.html#mapping-declaration-class

id

<id
   name="propertyName"
   type="typename"
   column="column_name"
   
   unsaved-value="any|none|null|id_value"      (default: null)
   access="field|property|ClassName">      (default: property)
   
   <generator class="generatorClass"/>
</id>

http://www.hibernate.org/hib_docs/reference/en/html/mapping.html#mapping-declaration-id

types

• integer, long, short, float, double, character, byte, boolean

Java primitives or wrapper classes to appropriate SQL types

• string

java.lang.String to VARCHAR (or Oracle VARCHAR2)

• date, time, timestamp

java.util.Date to SQL types DATE, TIME and TIMESTAMP

• calendar, calendar_date

java.util.Calendar to SQL types TIMESTAMP and DATE

• big_decimal

java.math.BigDecimal to NUMERIC (or Oracle NUMBER)

• locale, timezone, currency

java.util.Locale, java.util.TimeZone and java.util.Currency to VARCHAR (or Oracle VARCHAR2)

• binary

byte arrays to an appropriate SQL binary type.

• text

Maps long Java strings to a SQL CLOB or TEXT type.

• serializable

Maps serializable Java types to an appropriate SQL binary type

http://www.hibernate.org/hib_docs/reference/en/html/mapping.html#mapping-types

Generate Class

• native

Picks identity, sequence or hilo depending upon the underlying database.

• increment

Generates unique identifiers

• identity

Identity columns in DB2, MySQL, MS SQL Server, Sybase and HypersonicSQL

• sequence

Sequence in DB2, PostgreSQL, Oracle, SAP DB, McKoi

• hilo

uses a hi/lo algorithm to efficiently generate identifiers

• uuid.hex 128-bit UUID algorithm

• assigned

The application to assign an identifier

• foreign

Uses the identifier of another associated object. Usually used in conjunction with a <one-to-one> primary key association.

Property

<property
   name="propertyName"
   
   column="column_name"      (default: property name)
   type="typename"
   update="true|false"       (default: true)
   insert="true|false"          (default: true)
   formula="arbitrary SQL expression"  
   access="field|property|ClassName"      (default: property)
/>

update – should property be included in updates

insert – should property be included in inserts

formula – used to compute a value rather than reading it

access – how Hibernate accesses the value in the object

http://www.hibernate.org/hib_docs/reference/en/html/mapping.html#mapping-declaration-property

Mapping Collections

Hibernate supports:

• Set
• Bag
• List
• Maps

Java Collection Information

API

http://java.sun.com/j2se/1.4.2/docs/api/java/util/package-summary.html

Overview

http://java.sun.com/j2se/1.4.2/docs/guide/collections/index.html

Set

Collection that does not allow duplicate entries

No order on the elements

Hibernate has own Set implementation

You can use any class that implements Set interface

java.util.HashSet

java.util.TreeSet

Bag

Collection that allows duplicate entries

No order on the elements

Hibernate has own Bag implementation

You can use any class that with the java.util.List interface

Hibernate does not maintain original order of elements

List Mapping

Collection that maintains order

Requires additional column in table

Map Mapping

Map is a collection indexed by keys (Dictionary)

Requires additional column in table for keys

Collection Mappings

<map
   name="propertyName"
   
   table="table_name"            (default: property name)
   schema="schema_name"
   lazy="true|false"            (default: false)
   inverse="true|false"            (default: false)
   cascade="all|none|save-update|delete|all-delete-orphan"    
            (default: none)
   sort="unsorted|natural|comparatorClass"   
   order-by="column_name asc|desc"
   where="arbitrary sql where condition"
   outer-join="true|false|auto"
   batch-size="N"                  (default: 1)
   access="field|property|ClassName"      (default: property)
>
   
   <key .... />
   <index .... />
   <element .... />
</map>

http://www.hibernate.org/hib_docs/reference/en/html/collections.html#collections-mapping

Many-to-one

<many-to-one
   name="propertyName"
   column="column_name"         
   class="ClassName"            
   cascade="all|none|save-update|delete"   
   outer-join="true|false|auto"      
   update="true|false"      
   insert="true|false"         
   property-ref="propertyNameFromAssociatedClass"
   access="field|property|ClassName"   
      unique="true|false"         
/>

Person Class

package cs683;
   
import java.util.HashSet;
import java.util.Set;
   
public class Person {
   String firstName;
   String lastName;
   Set addresses =  new HashSet();;
   long id;
   
   public Person () { super(); }
   
   public Person(String first, String last) {
      firstName = first;
      lastName = last;
   }
   
   public String getLastName() { return lastName; }
   public String getFirstName() { return firstName; }
   
   public void setFirstName( String name) { firstName = name; }
   public void setLastName( String name) {   lastName = name; }
   
   public long getId() { return id; }
   public void setId(long l) {id = l; }
   
   public String toString() {   return firstName + " " + lastName + id; }
   public Set getAddresses() { return addresses; }
   public void setAddresses(Set addresses) { this.addresses = addresses; }
   public void addAddress(EmailAddress newAddress) {
      addresses.add( newAddress);
   }
}

EmailAddress class

package cs683;
   
public class EmailAddress {
   String userName;
   String host;
   long id;
   
   public EmailAddress() { }
   
   public EmailAddress(String user, String host) {
      userName = user;
      this.host = host;
   }
   
   public String getHost() { return host; }
   
   public void setHost(String host) { this.host = host; }
   
   public long getId() { return id; }
   
   public void setId(long id) { this.id = id; }
   
   public String getUserName() { return userName; }
   
   public void setUserName(String userName) {
      this.userName = userName;
   }
}

Main

package cs683;
   
import java.util.List;
import java.util.Set;
   
import net.sf.hibernate.HibernateException;
import net.sf.hibernate.MappingException;
import net.sf.hibernate.Query;
import net.sf.hibernate.Session;
import net.sf.hibernate.SessionFactory;
import net.sf.hibernate.Transaction;
import net.sf.hibernate.cfg.Configuration;
   
public class Main {
   public static void main(String[] args) throws Exception {
      sampleWrite();
      sampleRead();
   }
   
   static Session getHibernateSession() throws MappingException,
         HibernateException, Exception
      {
      Configuration config = new Configuration();
      config.addClass(cs683.Person.class);
      config.addClass(cs683.EmailAddress.class);
   
      SessionFactory sessions = config.buildSessionFactory();
      Session session = sessions.openSession();
      return session;
      }

Main Continued

   static void sampleWrite() throws MappingException, HibernateException,
         Exception {
      Session session = getHibernateSession();
      Transaction save = session.beginTransaction();
      Person newPerson = new Person("Susan", "LittleBit");
      session.save(newPerson);
      EmailAddress bar = new EmailAddress("foo", "bar.aol.com");
      session.save(bar);
      EmailAddress cat = new EmailAddress("catwoman", "gmail.com");
      session.save(cat);
      newPerson.addAddress(cat);
      newPerson.addAddress(bar);
      save.commit();
      session.close();
      }
   
   static void sampleRead() throws MappingException, HibernateException,
         Exception {
      Session session = getHibernateSession();
      Query getPerson = 
         session.createQuery(" from Person p where p.lastName = 'LittleBit'");
      List result = getPerson.list();
      System.out.println("Number of Objects: " + result.size());
      System.out.println(result.get(0));
      Set addresses = ((Person) result.get(0)).getAddresses();
      System.out.println(addresses.getClass());
      session.close();
      }
   }

Variations

Cascading Saves

Person contains a collection of email addresses

When saving a person to also save the email addresses

• Cascade must be on

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

• Email Address must be registered with the session

Person newPerson = new Person("Susan", "LittleBit");
      session.save(newPerson);
      EmailAddress bar = new EmailAddress("foo", "bar.aol.com");
      session.save(bar);
      EmailAddress cat = new EmailAddress("catwoman", "gmail.com");
      session.save(cat);
      newPerson.addAddress(cat);
      newPerson.addAddress(bar);

Lazy Fetching

Only read email addresses from database when they are needed

<set name="addresses" 
      inverse="false" 
      cascade="save-update" 
      lazy=true
      table="EMAIL_ADDRESSES">
         <key  column="person_id"/>

   static void sampleRead() throws MappingException, HibernateException,
         Exception {
      Session session = getHibernateSession();
      Query getPerson = 
         session.createQuery(" from Person p where p.lastName = 'LittleBit'");
      List result = getPerson.list();
      System.out.println("Number of Objects: " + result.size());
      System.out.println(result.get(0));
   
      //Next line reads EmailAddress from database
      Set addresses = ((Person) result.get(0)).getAddresses();
      System.out.println(addresses.getClass());
      session.close();
      }

Beware of Lazy Fetching

   static void sampleRead() throws MappingException, HibernateException,
         Exception {
      Session session = getHibernateSession();
      Query getPerson = 
         session.createQuery(" from Person p where p.lastName = 'LittleBit'");
      List result = getPerson.list();
      session.close();
   
      System.out.println("Number of Objects: " + result.size());
      System.out.println(result.get(0));
   
      Set addresses = ((Person) result.get(0)).getAddresses();
      System.out.println(addresses.getClass());
      }

If lazy=false the above works fine

If lazy=true the above does not work

Queries - HQL

Hibernate Query Language

Docs

http://www.hibernate.org/hib_docs/reference/en/html/queryhql.html

Hibern8ide

Java program to test queries

Session session = getHibernateSession();
   
String queryString = " from Person p where p.lastName = 'Whitney'  ";
Query getPerson =  session.createQuery( queryString);
List result = getPerson.list();
   
session.close();

Examples of queries will just show the queryString

Examples will run in Hibern8ide as given

Running Hibern8ide

public class Main
   {
   public static void main(String[] args) throws Exception
      {
      Hibern8IDE.main(args);
      }
   }

Classpath needs all the normal Hibernate jar files plus:

• hibern8ide/hibern8ide.jar
• hibern8ide/lib/*.jar

where hibern8ide is part of the hibernate extensions download

Querying a Class

from Person
from EmailAddress
   
from java.lang.Object

from x

• Returns all object of type x from database
• Includes objects of subclasses of x

Controlling Number of Hits

Session session = getHibernateSession();
   
String queryString = " from Person p where p.lastName = 'Whitney'  ";
Query getPerson =  session.createQuery( queryString);
getPerson.setFirstResult(5);
getPerson.setMaxResults(20);
List result = getPerson.list();
   
session.close();

setFirstResult(5)

the first result returned is the fifth one found in the database

setMaxResults(20);

Return at most 20 results

Getting One Result

Session session = getHibernateSession();
   
String queryString = " from Person p where p.lastName = 'Whitney'  ";
Query getPerson =  session.createQuery( queryString);
getPerson.setMaxResults(1);
Person whitney = (Person) getPerson.uniqueResult();
   
session.close();

Don’t need a list if know we will get one result

Aliases

from Person p where p.lastName = 'Whitney'
   
from Person aPerson where person.lastName = 'Whitney'
   
from Person as aPerson where person.lastName = 'Whitney'

p & aPerson are aliases for Person object in rest of query

Restricting Queries

from Person p where p.lastName = 'Whitney'
   
from Person p where p.lastName like 'W%'
   
from Person p where p.lastName not like 'W%'
   
from Person p where p.lastName in ( 'Whitney', 'Tester' )
   
from Person p where p.age between 21 and 50
   
from Person p where p.age < 21
   
from Person p where p.lastName is null
   
from Person p where p.lastName is not null

like wildcard characters

• % matches any number of characters
• _ matches a single character

Basic SQL operators supported

Logical Operators

from Person p 
   where p.lastName like 'W%' 
   and p.firstName in ('Roger', 'Paul')
   
from Person p 
   where (p.lastName like 'W%' and p.firstName in ('Roger', 'Paul') )
   or p.lastName = 'Chen'

“and” “or” and “( )” can be used to combine expressions

Ordering Query Results

from Person p order by p.lastName
   
from Person p order by p.lastName asc
   
from Person p order by p.lastName desc
   
from Person p order by p.lastName asc, p.firstName
   
from Person p where p.lastName = 'Whitney' order by p.firstName

Properties of Properties

from People p where p.address.city = 'La Jolla'
   
from Person p where p.addresses.size > 1

Previous     visitors since 22-Nov-04     Next