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KRAD Data Layer
JPA Design
Eric Westfall
July 2013
What is JPA?
• “Java Persistence API”
• Framework for managing relational data from
Java applications
• Standardized approach developed through the
Java Community Process (JCP)
• Three main areas:
– API for storage/retrieval of entities
– JPQL (query language)
– Object/Relational Metadata
JPA Versions
• JPA has had three major version releases
– 1.0, 2.0, 2.1
• We are targeting JPA version 2.1
• Fairly recent, finalized April 2013
JPA 2.1 Features
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Converters
Bulk Operations
Stored Procedure support
Database Schema Generation
Entity Graphs
JPQL/Criteria enhancements
Unsynchronized Persistence Contexts
Vendor Support for JPA Versions
Vendor Neutrality
• Ideally we would like to stay vendor-neutral
and use only JPA features
• But unfortunately we can’t!
• Two gaps:
– Lack of programmatic access to mapping
metadata
– Lack of support for custom ID generation
strategies
• Fortunately, this list is fairly small.
Vendor Selection
• Team working on JPA support in KRAD are
recommending the use of EclipseLink as the
default JPA implementation
– Lazy loading semantics are the same as OJB,
therefore eases the transition
– Is the reference implementation of JPA
– Provides us an easy method for programmatic
read/write access to metadata
– Support for custom identifier generation
So why use JPA then?
• Why not just use EclipseLink-specific
annotations and functionality instead of JPA?
Design Time!
Design
Time!
Plugging JPA into KRAD Data Layer
Client Application Code
KRAD Data API
JPA Persistence
Provider
JPA
Metadata
Provider
EclipseLink
Database
EntityManager Configuration
• Spring provides
LocalContainerEntityManagerFactoryBean
• But we’ve created a simpler version to handle
setting up KRAD for JPA with EclipseLink
JpaPersistenceProvider
• save
– verify the data object is valid and writable
– perform "reference linking" (see KRAD Data Layer Design document
for information on linking)
– execute an EntityManager.merge(...)
– return the merged object
• find
– execute an EntityManager.find(...)
– return the result
• findMatching
– translate from the Rice QueryByCriteria to a JPA Query and execute it
translate the result of the query into Rice QueryResults and return it
• delete
– verify the data object is valid and writable
– execute an EntityManager.delete(...)
SharedEntityManager
• Provided by Spring
• Allows us to inject an EntityManager that is
shared across multiple classes
• Example usage with JpaPersistenceProvider
JPA Metadata Provider
• Provides metadata about Entities managed by
the persistence unit
• Relationships, collections, keys, etc.
• Pulls what it can from the pure JPA
“Metamodel”
• Gets the rest from EclipseLink-specific APIs
Sequences and Generated IDs
• For Oracle we use native sequences
• For MySQL we use “_S” tables to simulate
sequences
• Can implement similar behavior using an
EclipseLink “SessionCustomizer”
Converters
• Supported natively as of JPA 2.1!
• Allows for conversion between database and
java types
• For example, storing booleans as “Y” and “N”
character data in the database
• Boolean, KualiDecimal, KualiPercent,
KualiInteger, Encrypted values
Extension Framework
• In KNS, allowed for institutions to customize
database by adding tables with additional
columns and “linking” them to the delivered
parent table
• Required manual copy and modification of
OJB mapping files
• Using programattic metadata modification,
can do this programatically now with JPA +
EclipseLink
Custom DAO’s and Data Access
• It is still very likely that applications will
continue to need custom DAOs for certain
cases
• In these cases, simply create the DAO and
inject the shared EntityManager into it and
use the JPA apis directly
– JPQL
– Crteria Query
– Etc.
JPA with krad-data, services, and DAOs
Client Application Code
KRAD Data API
JPA Persistence
Provider
JPA
Metadata
Provider
EclipseLink
Database
Service API
Service Implementation
Data Access Object
Backend Development
1.
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6.
Create JPA entities, map with annotations
Wire EntityManagerFactory bean in Spring
Wire SharedEntityManager bean ins Spring
Inject into a JpaPersistenceProvider
Inject into a JpaMetadataProvider
Register both providers with
ModuleConfiguration
7. Use the KRAD DataObjectService!