Craig Russell

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JavaTM Data Objects 2.0 Preview
Craig Russell Architect Sun Java Enterprise System
This is the preview for Java Data Objects 2.0
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Presentation Objectives

• Java Data Objects Overview
• Current status of Java Data Objects
• Strategic goals of Java Data Objects
• Java Data Objects 2.0

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Presenter's Qualifications

• Architect, Sun Java Enterprise System
• Specification Lead, Java Data Objects
• JSR 12
• JSR 243
• Author of "Java Data Objects" published 2003,
  O'Reilly

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Java Data Objects Overview

• Transparent Persistence for Java
• Java objects mapped to database objects
• Application objects automatically retrieved,
  stored, updated
• No database code in Domain Objects
• NOT a Framework (but plays well with others)
• Runs with frameworks (app server, web server)
• Datastore independent
• Application interfaces
• life-cycle, query, transactions

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Java Data Objects Interfaces

• PersistenceManagerFactory
• bootstrap
• identifies data source
• PersistenceManager
• life-cycle (makePersistent, deletePersistent)
• Query
• filter collections of persistent instances
• Transaction
• begin, complete transactions

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Current Status

• Java Data Objects proposed as Java Specification
  Request 12 in May 1999
• 1.0 released April 2002
• 1.0.1 released August 2003
• New Java Specification Request for 2.0 proposed
  in 2004 JSR 243
• Vendors, Users working on detailed user interfaces

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Strategic Goals

• Easy to Use...
• natural programming model
• configuration and deployment
• In a Wide Variety of Environments...
• Java 2 Standard Edition (rich clients)
• application, web servers

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Goals for Java Data Objects 2.0

• Maintain JDO 1.0 Compatibility
• Standardize Mapping to Relational DB
• Multi-tier Development Improvements
• Usability Improvements
• Better Object Modeling
• Richer Queries
• More Vendor Support

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Standardize Mapping to RDBMS

• Simple Mapping
• Class lt-gt Table
• Field lt-gt Column
• 1-1 relationship lt-gt unique foreign key
• 1-many relationship lt-gt foreign key
• many-many relationship lt-gt join table
• Complex Mapping
• Inheritance strategies
• Multiple tables per class
• List, Map, Embedded

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Multi-tier Development

• Disconnected Object Graphs
• Disconnect objects from PersistenceManager
• Close PersistenceManager
• Modify disconnected objects
• send to different tier, or
• apply changes directly to objects
• Begin new transaction
• Reconnect objects to PersistenceManager
• Commit transaction (applies changes)
• Disconnected Objects keep original identity and
  version

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Usability (Bootstrap)

• How do you find a PersistenceManagerFactory?
• Java Data Objects 1.0 Properties
• javax.jdo.PersistenceManagerFactoryClass\
• com.sun.jdori.fostore.FOStorePMF
  javax.jdo.option.ConnectionURL\
• fostore/shared/databases/jdo/dbdir
  javax.jdo.option.ConnectionUserNamecraig
  javax.jdo.option.ConnectionPasswordfaster
  javax.jdo.option.Optimistictrue
• javax.jdo.option.RetainValuestrue
• javax.jdo.option.NontransactionalReadtrue

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Bootstrap

• JDO 1.0 Properties instance
• getPersistenceManagerFactory (Properties props)
• JDO 2.0 Properties loaded from
• stream
• getPersistenceManagerFactory (InputStream props)
• File (use to get a stream)
• getPersistenceManagerFactory (File propsFile)
• resource name (use to get a stream)
• getPersistenceManagerFactory (String
  propsResource)
• JDO 2.0 JNDI lookup
• getPersistenceManagerFactory (String name,
  Context c)

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Usability

• JDO 2.0 Transaction adds
• boolean getRollbackOnly()
• void setRollbackOnly()
• JDO 2.0 Query can be defined in metadata and
  accessed by name

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Better Object Modeling

• Persistent Abstract Class Support
• map abstract classes to tables
• map properties, fields to columns
• create new implementation instances
• Persistent Interface Support
• map interfaces to tables
• map properties to columns
• create new implementation instances
• use interfaces in queries

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Richer Queries
Preserve Expressability in SQL

• Projections
• Aggregates
• More String expressions
• More numeric, Map functions
• Paging query results
• Native SQL
• User-defined Result Class

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Projections

• JDO 1.0 query results are a subset of instances
  in the candidate collection
• JDO 2.0 query results can be projections of
• candidate collection instances
• variable instances
• fields
• parameters
• combinations of the above.

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Projections Example
Query q pm.newQuery (Employee.class,
"dept.name.startsWith(deptName)") q.declarePara
meters ("String deptName") q.setResult("name,
salary, boss") Collection names (Collection)
q.execute("RD")
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Aggregates

• Query Results can be aggregates
• Aggregates have standard semantics
• min
• max
• avg
• sum
• count
• Group by projected fields
• Having allows conditional filtering

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Aggregates Example
Query q pm.newQuery (Employee.class,
"dept.name.startsWith(deptName)") q.declarePara
meters ("String deptName") q.setResult("dept.name
, min(salary), max(salary)") q.setGrouping("dept.
name having count(dept.name) gt 1") Collection
names (Collection) q.execute("RD") for
(Object i (CollectionltObject gt) results)
println(i0, i1, i2)
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String Expressions

• toLowerCase(), toUpperCase()
• indexOf(String), indexOf(String, int)
• matches(String pattern)
• pattern is a subset of regular expressions
• (?i) global case-insensitive
• . match any one character
• . match any number (0 to n) of characters
• pattern is literal or parameter only
• substring(int), substring(int, int)

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Other Query Filter Methods

• Math.abs(numeric expression)
• Math.sqrt(numeric expression)
• Map.containsKey(Object)
• Map.containsValue(Object)

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Paging Query Results

• Improves performance for some applications
• Skips already-returned results
• Limits number of results
• Query.setRange (int fromIncl, int toExcl)
• default
• fromIncl 0
• toExcl Integer.MAX_VALUE

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User-Defined Result Class

• JDO 1.0 query results are of type Collection
• JDO 2.0 allows user to specify result class
• Primitive wrapper (unique results)
• CollectionltPrimitive wrappergt
• Object (projected or aggregate unique results)
• CollectionltObjectgt
• User-defined Class (unique results)
• CollectionltUser-defined Classgt

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ResultClass Example
class Employee private String name private
float salary private Department dept private
Employee boss
class Info public String name public Float
salary public Employee reportsTo
Query q pm.newQuery (Employee.class,
"dept.name deptName") q.declareParameters
("String deptName") q.setResult("name, salary,
boss as reportsTo") q.setResultClass(Info.class)
Collection results (Collection)
q.execute("RD") for (Info i
(CollectionltInfogt) results) println(i.name,
i.salary, i.reportsTo.name)
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Native SQL

• JDO 1.0 does not recognize SQL
• JDO 2.0 supports
• obtaining java.sql.Connection from
  PersistenceManager
• defining SQL queries
• may improve performance (good)
• makes query non-portable (bad)
• may support SQL-specific constructs (?)
• may allow SQL DBA more control (!)

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More Vendor Support

• Remove PersistenceCapable requirement
• Remove pre-processor, post-processor requirement
• Allow non-enhancer versions of JDO implementation
• All other compliance requirements remain

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JDO Strategic Goals
Standardize Relational Mapping Improve
Usability Extend Query Functionality Add Vendor
Support
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Craig Russell craig.russell_at_sun.com java.sun.com/p
roducts/jdo JDOCentral.com
JDO gives customers compelling persistence
solutions