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JavaTM Persistence API 2.0: An Overview

Sanjeeb SahooSr. Staff Engineer, Sun, an Oracle Company

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The following/preceding is intended to outline our general product direction. It is intended for

information purposes only, and may not be incorporated into any contract. It is not a

commitment to deliver any material, code, or functionality, and should not be relied upon in

making purchasing decisions.The development, release, and timing of any

features or functionality described for Oracle’s products remains at the sole discretion of

Oracle.

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JavaTM Persistence API: Brief History

• Java Persistence 1.0– Standardized object/relational mapping for Java

applications– Available as part Java EE 5 Platform or standalone– Covered most of the essential features

• Java Persistence 2.0– More and better increased application portability – Released in December 2009– Available as part of Java EE 6 Platform or standalone– Reference Implementation is EclipseLink– Available as part of GlassFish v3

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Key Interfaces

• EntityManagerFactory– Used to create entity managers– One entity manager factory per persistence unit

• EntityManager• Used to manage persistence context

• Entities read/written from database• Operations: persist, remove, find, refresh, createQuery,…

• Query, TypedQuery• Used for query configuration, parameter binding, query

execution

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Packaging

• Java SE (Standalone Java Application)– Jar file with entities, application classes and META-

INF/persistence.xml

• Java EE– War file

• WEB-INF/classes/META-INF/persistence.xml• WEB-INF/lib/entities.jar (with META-INF/persistence.xml)

– EJB jar• EJBs and entities and META-INF/persistence.xml

– EAR file• lib/entities.jar with META-INF/persistence.xml

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Bootstrapping

• Java SE (Standalone Java Application)– Persistence.createEntityManagerFactory

• Java EE– @PersistenceContext EntityManager em;– @PersistenceUnit EntityManagerFactory emf;

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JavaTM Persistence 2.0:New Features

• Expanded modeling capabilities• Additional O/R mapping options• Additions to Java Persistence query language• Metamodel API• Criteria API• Pessimistic locking• Standardization of many configuration options• Support for validation

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Object/Relational MappingEssentials

• Entities• Basic types

• Strings, integers, floats, decimals, …

• Embeddable classes• E.g., Address

• Relationships• One-to-one, one-to-many/many-to-one, many-to-many• Collections modeled with java.util Collection, Set, List, or Map• Customized via metadata: @JoinColumn, @JoinTable, etc.

• Inheritance• Single table, joined subclass, table per class (optional)

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JavaTM Persistence 2.0: Expanded modeling and mapping

• Collections of basic types• Collections of embeddables• Richer support for embeddable classes

– Multiple levels of embedding– Embeddable classes with relationships

• Persistently ordered lists• Improved map support

– Joins with additional columns– Ternary relationships

• Orphan deletion

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JavaTM Persistence 2.0: Expanded modeling and mapping

• Derived identities– Improved modeling for overlapping primary and foreign

keys

• Combinations of access types• Expanded relationship mapping options

– Unidirectional one-many foreign key mappings– One-one, many-one/one-many join table mappings

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Collections of Basic Types and Embeddables

• Collections of strings, integers, etc.• Collections of embeddables (e.g., Address, Detail)

• Specified by @ElementCollection

• Stored in “collection table”

• Customize mappings with:– @CollectionTable– @Column (for basic types)– @AttributeOverride, @AssociationOverride (for

embeddables)

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Collections of Basic Types

@Entitypublic class Person { @Id protected String ssn; protected String name; protected Date birthDate; ... @ElementCollection protected Set<String> nickNames; ...}

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Collections of Basic Types

PERSONSSN NAME BIRTHDATE

PERSON_SSN NICKNAMES PERSON_NICKNAMES

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Collections of Embeddable Types

@Entity public class Landlord { @Id String taxId; String name; @ElementCollection @CollectionTable(name=“rentals”) Set<Address> properties; ...}

@Embeddable public class Address { String street; String city; String state; ... }

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LANDLORD_TAXID STREET CITY STATE …

Collections of Embeddable Types

LANDLORD TAXID NAME …

RENTALS

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Multiple Levels of Embedding

@Entity public class Employee { @Id int empId; String name; ContactInfo contactInfo; . . . }

@Embeddable public class ContactInfo { @Embedded Address address; . . .}

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Embeddables with Relationships

@Entity public class Employee { @Id int empId; String name; ContactInfo contactInfo; . . . }

@Embeddable public class ContactInfo { @Embedded Address address; @OneToMany Set<Phone> phones; . . .}

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Persistently Ordered Lists

• Order is maintained in database by provider– Uses additional (integral) ordering column

• Specified with @OrderColumn• Provides alternative to @OrderBy

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Persistently Ordered Lists

@Entity public class CreditCard { @Id String cardNumber; @ManyToOne Customer customer; ... @OneToMany(mappedBy=“creditCard”) @OrderColumn(name=“TXORDER”) List<CardTransaction> transactionHistory; ...}

@Entity public class CardTransaction { @Id @GeneratedValue Long id; @ManyToOne @JoinColumn(name=“CARDID”) CreditCard creditCard; @Temporal(DATE) Date txDate; ...}

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CARDID ID TXDATE … TXORDERCARDTRANSACTION

OrderColumn

CREDITCARD CARDNUMBER …

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@Entity public class CreditCard { @Id String cardNumber; @ManyToOne Customer customer; ... @OneToMany(mappedBy=“creditCard”) @OrderColumn(name=“TXORDER”) @OrderBy(“txDate”) List<CardTransaction> transactionHistory; ...}

@Entity public class CardTransaction { @Id @GeneratedValue Long id; @ManyToOne @JoinColumn(name=“CARDID”) CreditCard creditCard; @Temporal(DATE) Date txDate; ...}

@OrderBy Alternative

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Generalized Maps

• Map key can be– Basic type– Embeddable– Entity

• Map value can be– Basic type– Embeddable– Entity

• Support for legacy join tables with additional columns

• Support for ternary relationships

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Generalized Maps

• Map collection is specified with– @ElementCollection, @OneToMany, @ManyToMany– Annotation is determined by map value

• Customize mapping with:– @CollectionTable (for element collection)– @JoinTable (for relationship)– @MapKeyColumn (for basic map key)– @MapKeyJoinColumn(s) (for entity key)– @AttributeOverride(s) using “key.” or “value.” syntax

(for embeddables)

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Generalized Maps

@Entitypublic class VideoStore { @Id Integer storeId; Address location; @ElementCollection @CollectionTable( joinColumn=@JoinColumn(name=“VIDEO_STOREID”)) Map<Movie, Integer> inventory; ...}

@Entitypublic class Movie { @Id String title; String director; ...}

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VIDEO_STOREID INVENTORY_KEY INVENTORYVIDEOSTORE_INVENTORY

Generalized Maps

VIDEOSTORESTOREID NAME STREET CITY STATE …

MOVIE TITLE DIRECTOR …

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Automatic Orphan Deletion

• Deletion of related entities when removed from relationship– For entities logically “owned” by “parent”– For one-to-one and one-to-many relationships

• Specified with orphanRemoval element– cascade=REMOVE is redundant

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Orphan Deletion

@Entitypublic class Order { @Id int orderId; ... @OneToMany(cascade=PERSIST, orphanRemoval=true) Set<Item> items;}

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Java Persistence Query Language:New Functionality

• Support for all new modeling and mapping features

• Operators and functions in select list• Case, coalesce, nullif expressions• Restricted polymorphism• Collection-valued input parameters• Date / time / timestamp literals

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New Operators

• INDEX– For ordered lists

• KEY, VALUE, ENTRY– For maps

• CASE, COALESCE, NULLIF– For case expressions and the like

• TYPE– For entity type expressions / restricted polymorphism

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Restricted Polymorphism, Collection-valued Input Parameters

SELECT eFROM Employee eWHERE TYPE(e) IN (PartTime, Contractor)

SELECT eFROM Employee e WHERE TYPE(e) IN :empTypes

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Criteria API

• Object-based API for building queries• Designed to mirror JPQL semantics• Strongly typed

– Based on type-safe metamodel of persistence unit– Heavy use of Java generics– Typing carries through to query execution as well

• Supports object-based or strong-based navigation

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Criteria API: Core Interfaces

• CriteriaQuery– Represents a query definition object– Used to add / replace / browse constituent query elements– select, from, where, orderBy, groupBy, having,… methods

• CriteriaBuilder– Factory for CriteriaQuery objects– Obtained from EntityManager or EntityManagerFactory– Used to create selections, expressions, restrictions,

orderings…

• Root– Query root

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Criteria API: Core Interfaces

• Join, ListJoin, MapJoin,…– Joins from a root or existing join

• Path– Navigation from a root, join, path

• Subquery• Parameter• TypedQuery

– Executable query object– Extends Query interface

• Tuple– Multiple-valued result type

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The World’s Simplest Query

SELECT c

FROM Customer c

CriteriaBuilder cb = ...;

CriteriaQuery<Customer> cq = cb.createQuery(Customer.class);

Root<Customer> c = cq.from(Customer.class);

cq.select(c);

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Joins and Navigation

SELECT c

FROM Customer c join c.orders o

CriteriaBuilder cb = ...;

CriteriaQuery<Customer> cq = cb.createQuery(Customer.class);

Root<Customer> c = cq.from(Customer.class);

Join<Customer, Order> o = customer.join(“orders”);

cq.select(c);

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Joins and Navigation: What’s the Problem?

SELECT c

FROM Customer c join c.orders o

CriteriaBuilder cb = ...;

CriteriaQuery<Customer> cq = cb.createQuery(Customer.class);

Root<Customer> c = cq.from(Customer.class);

Join<Customer, Order> o = customer.join(“wombats”);

cq.select(c);

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Metamodel

• Abstract, “schema-level” view of managed classes of persistence unit– Entities, mapped superclasses, embeddables, and their

attributes and relationships

• Accessible at runtime– EntityManagerFactory.getMetamodel()– EntityManager.getMetamodel()

• Useful for frameworks• Provides foundation for type-safe queries• Can be materialized as static metamodel classes

– Use javac + annotation processor

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Type-safe Navigation

SELECT c

FROM Customer c join c.orders o

CriteriaBuilder cb = ...;

CriteriaQuery<Customer> cq = cb.createQuery(Customer.class);

Root<Customer> c = cq.from(Customer.class);

Join<Customer, Order> o = customer.join(Customer_.orders);

cq.select(c);

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Optimistic Locking

• Assumes read-committed isolation, deferred writes– Short term read-locks– Long term write-locks

• Layered on top of @Version use– Verify version for updated entities before transaction

commit

• Lock Modes– OPTIMISTIC (READ)– OPTIMISTIC_FORCE_INCREMENT (WRITE)

• “READ” lock => verify version for clean data• “WRITE” lock => update version for clean data

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Pessimistic Locking

• Grab database locks upfront• Lock Modes

– PESSIMISTIC_READ– PESSIMISTIC_WRITE– PESSIMISTIC_FORCE_INCREMENT

• Normal (default) pessimistic locking– Persistent state of entity (except element collections)– Relationships where entity holds foreign key

• Extended pessimistic locking– Uses javax.persistence.lock.scope property (EXTENDED)– Element collections and relationships in join tables– Phantoms are possible

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Pessimistic Locking

@Stateless public class HRBean { ... @PersistenceContext EntityManager em; ... public void giveRaises(int deptId) { Department dept = em.find(Department.class, deptId, LockModeType.PESSIMISTIC_READ); if (dept.getBudget() > 100000) { Query q = em.createQuery( “SELECT emp ” + “FROM Employee emp ” + “WHERE emp.dept.id = ” + deptId); q.setLockMode(LockModeType.PESSIMISTIC_WRITE); List = q.getResultList(); // update employee salaries selectively... } }}

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Locking APIs

• EntityManager methods: lock, find, refresh• Query / TypedQuery methods: setLockMode,

setHint• NamedQuery annotation: lockMode element

• javax.persistence.lock.scope property• javax.persistence.lock.timeout hint

• PessimisticLockException (if transaction rolls back)

• LockTimeoutException (if only statement rolls back)

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Second Level Cache APIs

• APIs and control options added for portability• Cache interface methods: evict, evictAll, contains• @Cacheable + shared-cache-mode XML element

– ALL, NONE, ENABLE_SELECTIVE, DISABLE_SELECTIVE

• Properties for find, refresh, setProperty methods– javax.persistence.cache.retrieveMode property

• USE, BYPASS– javax.persistence.cache.storeMode property

• USE, BYPASS, REFRESH

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Validation

• Leverages work of Bean Validation JSR (JSR 303)• Automatic validation upon lifecycle events

– PrePersist– PreUpdate– PreRemove

• persistence.xml validation-mode element– AUTO– CALLBACK– NONE

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Validation

@Entity public class Employee { @Id Integer empId; @NotNull String name; Float salary; @Max(15) Integer vacationDays; @Valid Address worksite; ...} @Embeddable public class Address { @Size(max=30) String street; @Size(max=20) String city; @Size(min=2,max=2) String state; @Zipcode String zipcode; ...}

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Standard Configuration Properties

• javax.persistence.jdbc.driver• javax.persistence.jdbc.url• javax.persistence.jdbc.user• javax.persistence.jdbc.password• . . .

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JPA 2.1 Candidate Featureshttp://jcp.org/en/jsr/detail?id=338

Multi-tenancy Support for stored procedures, vendor function Update and Delete Criteria queries, JPQL ↔

Criteria Query by Example Support for schema generation UUID generator type Persistence Context synchronization control Dynamic definition of PU Additional event listeners

NEW

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Summary

• Expanded modeling capabilities• Additional O/R mapping options• Additions to Java Persistence query language• Metamodel API• Criteria API• Pessimistic locking• Standardization of many configuration options• Support for validation• Improved portability

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Resources

• Java Persistence 2.0 Specification http://jcp.org/en/jsr/detail?id=317

• Reference Implementation is EclipseLink http://www.eclipse.org/eclipselink

• Available as part of Java EE 6 with GlassFish http://glassfish.org

• Book: Pro JPA 2 (Keith & Schincariol)

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The following/preceding is intended to outline our general product direction. It is intended for

information purposes only, and may not be incorporated into any contract. It is not a

commitment to deliver any material, code, or functionality, and should not be relied upon in

making purchasing decisions.The development, release, and timing of any

features or functionality described for Oracle’s products remains at the sole discretion of

Oracle.