Persisting Your Objects In The Database World @ AlphaCSP Professional OSS Convention 2006

Copyright AlphaCSP, The 1st Java open source convention Israel 2006

The 1st Java professional open source

Convention – Israel 2006


Persisting Your Objects in the

Database World

Baruch SadogurskyAlphaCSP

Page 3Copyright AlphaCSP, The 1st Java open source convention Israel 2006

Agenda

• O/R mapping– Problem definition– Past, current and future solutions

overview• Getting started with Hibernate

– Concepts– Architecture– Answering O/R mapping problems– Step by step demo

• Hibernate “Hot Stuff”


O/R Mapping

The problem, the solutions


Software Infrastructure Components

Transaction management

Security management

Availability ensuring

Saving and restoring objects


The Object-Relational Impedance Mismatch

• Portability• Inheritance mapping• Associations mapping• Object graph navigation


Infrastructure Development Bottleneck

Application Development

Infrastructure Development

20%

80%

Work Harder

Work Smarter

Application Development

Infrastructure Development

80%

20%


Solutions – Entity EJBs (1.x – 2.x)

• Part of J2EE EJB (1.x – 2.x) spec.• Intrusive persistence• Can’t be used outside of EJB

container• Difficult to port• Complicated programming model• Performance issues• No support for inheritance• Irrelevant technology


Solutions – TopLink

• Oracle product • Implements EJB 3.0• Excellent solution• Closed-source• Pricy


Solutions –JDO

• Part of J2EE spec.• Implementations mainly use

bytecode injection• Both closed-source and open-

source implementations• Mapping not standardized


Solutions – Hibernate



• Natural programming model• Support for ultra-fine-grained

object models• No build-time bytecode

enhancement• Extreme scalability• Detached objects support• Transitive persistence



• Integration• Support• Part of JBoss JEMS• De-facto standard• The query language• Support for "application"

transactions • Free / open source


Solutions –EJB 3.0

• The persistence API and query language in JSR-220 inspired by Hibernate

• De-jure standard• Gavin King, the author of Hibernate

is active in the expert group• “The Next Generation of EJB

Development” lecture by Frederic Simon covers EJB 3 in deep


Getting Started With Hibernate


Persistence Architecture

• From “Hibernate in Action”


Persistence Life Cycle

• From “Hibernate in Action”


Persistence Engine

• Non intrusive persistence

Database

POJOs

Mapping data

Session(Persistence Engine)


Database Manipulations

• Object-to-database and vice-versa manipulations are done with the Session methods

• Queries are submitted in Hibernate Query Language (HQL)– SQL-like syntax– Object orientation


HQL Example

• Same results in:– SQL:

SELECT cust.name, cust.address, cust.phone, cust.id, cust.current_order FROM customers cust, stores store, locations loc, store_customers sc,product prod WHERE prod.name = 'widget‘ AND store.loc_id = loc.id AND loc.name IN ('Melbourne', 'Sydney') AND sc.store_id = store.id AND sc.cust_id = cust.id AND prod.id = ALL(SELECT item.prod_id FROM line_items item, orders o WHERE item.order_id = o.id AND cust.current_order = o.id);

– HQL:select cust from Product prod, Store store

inner join store.customers cust where prod.name = 'widget' and store.location.name in ('Melbourne', 'Sydney')

and prod = all elements(cust.currentOrder.lineItems);


Criteria-Database Manipulations

• Queries have drawbacks• Unusual solution – Criteria API

– Java objects as filters

• Some limitations apply• Criteria by Example


Demo Class Diagram

-id : long+title : string+author : string+publicationDate : string+category : string+price : double+count : int+tracks : Track

CompactDisk

-id : long+name : string+duration : long+cd : CompactDisk

Track

+cd

1

+tracks

*

test.cd

PK CD_ID

CD_TITLE CD_AUTHOR CD_PUBLICATION_DATE CD_CATEGORY CD_PRICE CD_COUNT

test.track

PK TRACK_ID

TRACK_NAME TRACK_DURATIONFK1 CD_ID


Demo O/R mapping1 <hibernate-mapping>

2 <class name=“…CompactDisk" table="CD">

3 <id name="id" column="CD_ID“…>

4 <generator class="native"/>

5 </id>

6 <property name="title" column="CD_TITLE"/>

7 <property name="author" column="CD_AUTHOR"/>

8 <property name="publicationDate" column="CD_PUBLICATION_DATE"/>

9 <property name="category" column="CD_CATEGORY"/>

10 <property name="price" column="CD_PRICE"/>

11 <property name="count" column="CD_COUNT"/>

12 <bag name="tracks“ …>

13 <key column="TRACK_ID"/>

14 <one-to-many class=“…Track"/>

15 </bag>

16 </class>

17 </hibernate-mapping>

1 <hibernate-mapping>

2 <class name=“…Track" table="TRACK">

3 <id name="id" column="TRACK_ID" …>

4 <generator class="native"/>

5 </id>

6 <property name="name" column="TRACK_NAME"/>

7 <property name="duration" column="TRACK_DURATION"/>

8 <many-to-one name="cd" column="CD_ID" class=“…CompactDisk" not-null="true"/>

9 </class>

10 </hibernate-mapping>


Hibernate Demo


Hibernate “Hot Stuff”


Hibernate Annotations

• In Hibernate 2 mappings can be declared in:– XML .hbm.xml files– XDoclet

• Hibernate 3 introduces additional way of mapping by metadata in Java 5 annotations– Tools support– Build-time validation– Part of EJB 3 spec. (JSR 220)

• “The Next Generation of EJB Development” lecture by Frederic Simon covers EJB 3 Annotations in deep


Annotations Example

1 @Entity 2 public class AnnoTrack { 3 4 @Id 5 private Long id; 6 private String name; 7 private long duration; 8 @ManyToOne 9 private CompactDisk cd; 10 private Calendar calendar; 11 @Transient 12 private Integer internalSerial; 13 // Getter/setter and business methods 14 }


User-Defined Types

• Mapping other properties to single column– Boolean.TRUE to 1

• Mapping composite types to more than one column– Person to PERSON.FIRST_NAME and PERSON.LAST_NAME


Automatic Dirty Checking

• Changes in persistent object are monitored by Hibernate

• Manipulate the objects by regular Java means

• All the changes will be persisted during flush

• Session caches all the objects, associated with it to perform the check


• For multi-tier applications, running in different VMs

• Same objects are sent to the web tier, changed there and then sent back to the backend tier

• Hibernate knows which part of subgraph to update

• Hibernate distinguishes between reattached and newly added objects

Detached Object Support


• Bidirectional transitioning from and to the mapping file

• ReverseEngTool – useful when legacy DB is present

• SchemaExport – useful for automated creation of a fresh DB

Roundtrip Tools


Second Level Cache

2nd L

evel

Cac

he

Clu

ster

ed D

atab

ase

Database

Database

Database

Hib

erna

te C

ore

Session

Session

Session


Second Level Cache

• Session – transaction-level cache• Second-level cache levels:

– JVM– Cluster– Clustered

• Pluggable architecture• “Taking Control over Clustering

Caching and Data Distribution” lecture by Eran Haggiag and Avishay Halperen covers JBoss TreeCache in deep


Lazy Initialization – The Problem

• Objects may refer to huge collections of other objects– If Category was object, refer to all

CDs of that Category

• Transitive persistence should bring them all from the database even if they aren’t needed


Lazy Initialization – The Solution

• By default a collection is fetched only when the application invokes an operation upon that collection

• Filters can be used to initialize the collection partially or to get its size

• Beware! Hibernate does not support lazy initialization for detached objects


Statistics & JMX management

• Hibernate can expose metrics of SessionFactory in 2 ways:– Statistics object, retrieved from SessionFactory

– StatisticsService JMX MBean

• Metrics:– Related to the general Session usage– Related to the entities, collections, queries,

and caches as a whole (aka global metrics)– Detailed, related to a particular entity,

collection, query or cache region


Lifecycle Callbacks

• Actual operations (load, save, update) are performed by default implementation of lifecycle listeners

• You can extend the default implementation to add additional behavior


XML Data Binding

• Another way to represent data – XML trees• Hibernate let you map DOM objects

– instead of POJOs– in addition to POJOs


Stored procedures & hand-written SQL

• It is possible to specify handwritten SQL (including stored procedures)

• Utilize database specific features • Provides migration path from a

direct SQL/JDBC based application to Hibernate

• Can be created programmatically or declaratively


Documentation of generated SQL

• Hibernate can generate SQL statements with embedded comments

• Makes it easy to discover the source of a misbehaving query


References

• http://www.alphacsp.com• Hibernate official site• Reference Documentation• ”Hibernate in Action” book

– by Christian Bauer and Gavin King

• ”Pro Hibernate 3” book• “Hibernate: A Developer's Notebo

ok” book


Your Turn Now

Q & A


The 1st Java professional open source

Convention – Israel 2006

Persisting Your Objects In The Database World @ AlphaCSP Professional OSS Convention 2006

Technology

ejb development

level cache

mapping gt

common attributes

reflection

ip multicast

class dynamic

private field