Entity Beans

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Entity Beans

• Container Managed Persistence

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Entity Beans

• Represents a business entity in persistent
  storage
• Persistent
• Allow shared access
• Multiple Clients
• Have primary keys

3
Container Managed Persistence

• Container automatically generates database access
  calls
• Entity Manager
• Handles Objects Interaction with database
• No database access code in your code
• Makes code more portable, container generates
  correct SQL to match database
• Uses _at_Entity annotation to declare POJO as and
  entity bean

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CMP Entity Bean Classes

• Any Plain Old Java Object can be annotated as an
  Entitiy bean
• But
• Can be automatically generated from database
  definition

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Container Managed Fields

• The CMP entity bean has some container managed
  fields
• These are specified using the _at_Column(namefieldn
  ame) annotation
• _at_Id specifies the primary key field
• _at_GeneratedValue annotation shows a field that is
  automatically generated by the database
  (autoincrement)

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Entity Beans use

• An Entity Manager is used to access an entity
  bean
• An entity manager is included in a session bean
  using the
• _at_PersistenceContext(unitNameejbPUname)
• Protected EntityManager em
• Using the Entity Manager to find an instance
• em.find(sbAppejb.Srecord.class,StudentID)
• Storing a new Value
• Create new object MyRecord
• em.persist(MyRecord)

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• An entity manager is included in a servlet using
  the
• _at_PersistenceUnit(unitNameejbPUname)
• Protected EntityManagerFactory emf
• Protected EntityManager em
• ememf.createEntityManager()
• Used as in Session beans
• Used this way as Entity Manager not thread safe

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Using Named Queries

• Autogenerated Entity beans will have named EJBQL
  queries already defined
• E.g
• _at_NamedQueries(_at_NamedQuery(nameSrecord.findByNam
  e,querySELECT s FROM Srecord s where s.name
  name......)
• Use in session bean and servlets
• Query query em.createNamedQuery(Srecord.findByN
  ame)
• query.setParameter(name,name)
• return query.getResultList()

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Creating Queries

• You can create your own queries in session bean
  and servlets
• Query query em.createQuery(SELECT s FROM
  Srecord s where s.studentID gt studentID)
• query.setParameter(studentID, studentID)
• return query.getResultList()

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Bean Managed Persistence

• You write the code to access the database (not in
  Ejb3)
• More under your control
• Suitable for more complex interaction with
  database
• Not as portable if migrating to different
  database back end
• Not recommended

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Entity Bean Life Cycle
unsetEntityContext
setEntityContext
remove ejbRemove
ejbPassivate
ejbActivate
create setSessionContext ejbCreate
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Netbeans/mysql setup

• Netbeans requires a password for the database
  connection used
• So create a test user with test password on mysql
• grant all on . to test_at_localhost identified by
  test

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Summary
Main points to remember Container managed
persistence Entity Manager to interact with the
database