Topics in Enterprise Information Management

Transcription

1 Topics in Enterprise Information Management Dr. Ilan Kirsh JPA Basics

2 Object Database and ORM Standards and Products ODMG 1.0, 2.0, 3.0 TopLink, CocoBase, Castor, Hibernate,... EJB 1.0, EJB 2.0: Entity Beans / CMP IBM WebLogic, Bea WebSphere, Oracle, JBoss,... Java Data Objects (JDO) 1.0, 2.0 Solarmetric KODO, JPOX,... ObjectStore, Versant, ObjectDB JDO Implementations Java Persistence API 1.0 (JPA, EJB 3.0) TopLink / TopLink Essentials (Oracle) KODO / Open JPA (BEA / Solarmetric) Hibernate (Red Hat / JBoss) Persistence Providers 2

3 Entities

4 JPA Entities An entity class is a user defined persistable class that represents a domain model object. Annotated (or equivalent XML). Has a public / protected no-arg constructor. Should not be declared as final and should not have final methods. Top level entity class must declare an id using the Id annotation (or equivalent XML) to represent the persistent identity (primary key). 4

5 The Persistent State Persistent state can be managed either as fields or as properties by get / set methods. Accordingly, JPA annotations can be set on fields or on get methods. Mixing field access mode and property access mode in one entity class is not allowed. Fields with the transient modifier and fields and properties with annotation are excluded from the persistent state. 5

6 Persistent Fields / Properties Persistent fields must: not be static or final. have private, package or protected access. be accessed directly only from the entity. Persistent properties must have non final JavaBean style set (setproperty) and get (getproperty or isproperty) methods with protected or public access. Declared type must be persistable. 6

7 Persistable Types Java primitive types (byte, char, short, int, long, float, double, boolean) Java serializable types (including String primitive wrappers, BigInteger, BigDecimal, java.util.date, java.util.calendar, java.sql.date, java.sql.time, java.sql.timestamp, and user-defined serializable types). byte[], Byte[], char[], and Character[] enum types Entity types and embeddable classes Collections of entity types (must be declared as Collection, List, Set or Map). 7

8 Sample Entity

9 The Point Class public final class Point { public float x; public float y; Point(float x, float y) { this.x = x; this.y = y; } } public final String tostring() { return "(" + x + ", " + y + ")"; } 9

10 Making Point an public final class private long id; public private float x; public private float y; Point() {} Point(float x, float y) { this.x = x; this.y = y; } public float getx() { return x; } public float gety() { return y; } public final String tostring() { return "(" + x + ", " + y + ")"; } } 10

11 The Point Entity (Field public class private long id; private float x; private float y; Point() {} Point(float x, float y) { this.x = x; this.y = y; } public float getx() { return x; } public float gety() { return y; } public String tostring() { return "(" + x + ", " + y + ")"; } } 11

12 The Point Entity (Property public class Point { private long id; private float x; private float y; Point() {} Point(float x, float y) { this.x = x; this.y = y; } public void setid(long id) { this.id = public long getid() { return id; } public void setx(float x) { this.x = x; } public float getx() { return x; } public void sety(float y) { this.y = y; } public float gety() { return y; } public String tostring() { return "(" + x + ", " + y + ")"; } } 12

13 Persistence Unit

14 Persistence Unit A persistence unit represents a set of entity classes + configuration (usually packaged in a JAR file). META-INF/persistence.xml <persistence> <persistence-unit name="shapes" transaction-type="resource_local"> <provider>...</provider> <class>shapes.point</class> <properties>... </properties> </persistence-unit> </persistence> 14

15 TopLink Provider and Properties Provider oracle.toplink.essentials.ejb.cmp3.entitymanagerfactoryprovider Useful Properties <property name="toplink.jdbc.driver" value="org.apache.derby.jdbc.clientdriver"/> <property name="toplink.jdbc.url" value="jdbc:derby://localhost:1527/shapes"/> <property name="toplink.target-database" value="derby /> <property name="toplink.jdbc.user" value="app"/> <property name="toplink.jdbc.password" value="app"/> <property name="toplink.ddl-generation" value="create-tables"/> <property name="toplink.logging.level" value="info"/> <!-- OFF, SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST --> 15

16 Hibernate Provider and Properties Provider org.hibernate.ejb.hibernatepersistence Useful Properties <property name="hibernate.connection.driver_class" value="org.apache.derby.jdbc.clientdriver"/> <property name="hibernate.connection.url" value="jdbc:derby://localhost:1527/shapes"/> <property name="hibernate.dialect" value="org.hibernate.dialect.derbydialect"/> <property name="hibernate.connection.password" value="app"/> <property name="hibernate.connection.username" value="app"/> <property name="hibernate.hbm2ddl.auto" value="update"/> <property name="hibernate.show_sql" value="true"/> 16

17 Persistence API

18 JPA Basic API Package javax.persistence: Persistence EntityManagerFactory EntityManager EntityTransaction Query Annotations, Enums and Exceptions 18

19 Initialization and Cleanup Obtaining an EntityManager EntityManagerFactory emf = Persistence.createEntityManagerFactory( "Shapes"); EntityManager em = emf.getentitymanager(); Cleanup em.close(); emf.close(); 19

20 Persisting Entities Entity Persisting em.gettransaction().begin(); Point point = new Point(100, 100); // point is a "new" unmanaged object em.persist(point); // point is a "managed" object em.gettransaction().commit(); // point is stored in the database 20

21 The Persistence Context A persistence context represents the collection of entities that are managed by the persistence provider. Every EntityManager in Java SE has its own persistence context. Persistence Context operations: Check if object belongs to persistence context: boolean ismanaged = em.contains(point); Refresh the state of the object from the database: em.refresh(point); Synchronize the persistence context to the database: em.flush(); Clear the persistence context: em.clear(); 21

22 Retrieving Entities Retrieval by Id Point point = em.find(point.class, 1); System.out.println(point); Retrieval by Query Query query1 = em.createquery( "select p from Point p"); List<Point> resultlist = (List<Point>)query1.getResultList(); for (Point point : resultlist) System.out.println(point); Query query2 = em.createquery( "select p from Point p where p.x = 100"); Point point = (Point)query2.getSingleResult(); System.out.println(point); 22

23 Updating and Removing Entities Entity Updating em.gettransaction().begin(); Point point = em.find(point.class, 1); if (point!= null) point.setx(900); em.gettransaction().commit(); Entity Removing em.gettransaction().begin(); Point point = em.find(point.class, 1); if (point!= null) em.remove(point); em.gettransaction().commit(); 23

24 Update Tracking Implementation Storing all the managed objects to the database on every flush or commit. Keeping the original content of every retrieved object and detecting updates by comparing up to date content to old content on every flush or commit. Using proxy classes for retrieved objects, detecting calls to setproperty methods. Using a byte code (or a source code) enhancer (as a post compiler or during class loading) replacing every JVM putfield operation with a tracking method. 24

25 Exercise Basic JPA Create a new empty Derby database. Define a Student entity with 3 fields: long id String firstname, lastname Write a Java program that stores a few Student instances in the database. Write a Java program that retrieves and displays the Student instances. 25