There are several competing persistence technologies available for Java.
Two of these are "standardised" (via the JCP). When developing your application you need
to choose the most appropriate technology for your needs. Java Data Objects (JDO)
has been a standard since 2001 with the release of JDO1. It was improved with the release
of JDO2. Just to confuse issues the Java Persistence API (JPA) was approved
in its JPA1 form, and JDO2.1/JDO2.2 provide updates to JDO2 building on some of the new
features of JPA1. Below we show some of the differences of these 2 standards to give you
assistance in selecting what you need. Highlighted in bold are the notable differences where one
specification provides something not available in the other.
| Feature | JDO2.1 | JPA1 |
|---|
| JDK Requirement | 1.3+ | 1.5+ |
| Usage | J2EE, J2SE | J2EE, J2SE |
| Persistence specification mechanism | MetaData, Annotations | MetaData, Annotations |
| Datastore supported | Any | RDBMS only |
| Restrictions on persisted classes | no-arg constructor (could be added by compiler/enhancer) | No final classes. No final methods. Non-private no-arg constructor. Identity Field.
Version Field. |
| Ability to persist "transient" fields | Yes | No |
| Persist static/final fields | No | Not specified |
| Transactions | Pessimistic, Optimistic | Optimistic |
| Object Identity | datastore-identity, application-identity | application-identity |
| Object Identity generation | Sequence, Table, Identity, Auto, UUID String, UUID Hex | Sequence, Table, Identity, Auto |
| Change objects identity | Throw exception when not allowed | Undefined !! |
| Supported types | Java primitive types, wrappers of primitive types, java.lang.String, java.lang.Number, java.math.BigInteger, java.math.BigDecimal,
java.util.Currency, java.util.Locale, java.util.Date, java.sql.Time, java.sql.Date, java.sql.Timestamp, java.io.Serializable,
boolean[], byte[], char[], double[], float[], int[], long[], short[],
java.lang.Object, interface,
Boolean[], Byte[], Character[], Double[], Float[], Integer[], Long[], Short[], BigDecimal[], BigInteger[], String[],
PersistenceCapable[], interface[], Object[], Enums,
java.util.Collection, java.util.Set, java.util.List, java.util.Map,
Collection/List/Map of simple types, Collection/List/Map of reference (interface/Object) types,
Collection/List/Map of persistable types
| Java primitive types, wrappers of the primitive types, java.lang.String, java.math.BigInteger, java.math.BigDecimal,
java.util.Date, java.util.Calendar, java.sql.Date, java.sql.Time, java.sql.Timestamp, java.io.Serializable,
byte[], Byte[], char[], Character[], Enums,
java.util.Collection, java.util.Set, java.util.List, java.util.Map
Collection/List/Map of persistable types |
| Embedded Fields | Embedded persistent objects, Embedded Collections, Embedded Maps | Embedded persistent objects |
| Access a non-detached field | Throw exception | Undefined !! |
| Inheritance | Each class has its own strategy | Root class defines the strategy |
| Operation cascade default | persist, (delete) | |
| Operation Cascade configuration | delete | persist, delete, refresh |
| Query Language | JDOQL, SQL | JPQL, SQL |
| Query candidates | Candidate without subclasses, Candidate and its subclasses | Candidate and its subclasses |
| Query language case sensitivity | JDOQL lowercase/UPPERCASE | JPQL case-insensitive |
| Query language aliases | Not in JDOQL | Yes in JPQL |
| Object retrieval control | Lazy loading, eager fetching, fetch groups | Lazy loading, eager fetching |
| Bulk update/delete | JDOQL Bulk Delete | JPQL Bulk Delete, JPQL Bulk Update |
| RDBMS Schema Control | Tables, columns, PK columns, PK constraints, FK columns, FK constraints, index columns,
index constraints, unique key columns, unique key constraints | Tables, columns, PK columns, FK columns, unique key columns |
| ORM Relationships | Full range of Collection, Map, List, Array, 1-1, 1-N, M-N using
PC, Non-PC and interface objects | Basic 1-1, 1-N, M-N only. Collection<NonPC>, Map<NonPC> in JPA2 |
| Default ORM column size | 256 | 255 |
| Default ORM identifiers (tables/columns) | No | Yes |
| Default ORM mappings | Yes, JDBC types defined for Java types | No |
| Caching interface | L2 Caching API | Caching API in JPA2 |
As an overall conclusion "JPA1" is a subset of what is already available in "JDO2".
