Container Managed Relationships CMR

1
Container Managed Relationships(CMR)

• Source
• Enterprise JavaBeans, 3rd Edition, Richard
  Monson-Haefel

2
CMR

• Enabled with the EJB 2.0
• EJB 1.1 had support for persistent fields but not
  relationships
• Extends the abstract schema of the Entity Bean
• Abstract accessors must be defined for CMR fields
• CMR uses only Local Interfaces
• Only EJBs deployed together in the same
  deployment descriptor may have relationships with
  one another
• use same database and JVM

3
Seven Relationship Types

• One-to-One (unidirectional, bidirectional)
• One-to-Many (unidirectional, bidirectional)
• Many-to-One (unidirectional)
• Many-to-One and One to Many bidirectional
  identical
• Many-to-Many (unidirectional, bidirectional)

4
Defined and Initialized in the EJBClass

• public abstract class BorrowerEJB implements
  EntityBean
• public abstract void setId(String id)
• public abstract String getId()
• public abstract void setIdentity(PersonLocal
  person)
• public abstract PersonLocal getIdentity()
• //create transaction does not complete until both
  the ejbCreate and ejbPostCreate are called
• public String ejbCreate(PersonLocal identity)
  throws BorrowerException
• setId(identity.getId()) //primary key
  values must be set in ejbCreate
• return null
• public void ejbPostCreate(PersonLocal
  identity)
• setIdentity(identity) //relationships
  must be set in ejbPostCreate

id will be defined as a CMP Field
identity will be defined as a CMR Field
5
Used in the EJB Class

• public String getName()
• return getIdentity().getFirstName() " "
  getIdentity().getLastName()
• public String getPhoneNumber()
• return getIdentity().getPhoneNumber()
• public String getAddress()
• return getIdentity().getAddress()

6
Defined in ejb-jar.xml

• ltejb-jargt
• ltenterprise-beansgt
• ltentitygt
• ...
• lt/entitygt
• ...
• lt/enterprise-beansgt
• ltrelationshipsgt
• ltejb-relationgt lt!-- Borrower(0..1)-gt(1)Perso
  n (unidirectional) --gt
• ltejb-relation-namegtBorrower-Personlt/ejb-r
  elation-namegt
• ...
• lt/ejb-relationgt
• ...
• lt/relationshipsgt
• lt/ejb-jargt

7
Defining Borrower-gtPersonin ejb-jar.xml

• ltejb-relationgt lt!-- Borrower(0..1)-gt(1)Person
  (unidirectional) --gt
• ltejb-relation-namegtBorrower-Personlt/ejb-relatio
  n-namegt
• ltejb-relationship-rolegt
• ltejb-relationship-role-namegtBorrower-to-Iden
  titylt/ejb-relationship-role-namegt
• ltmultiplicitygtOnelt/multiplicitygt
• ltrelationship-role-sourcegt
• ltejb-namegtBorrowerlt/ejb-namegt
• lt/relationship-role-sourcegt
• ltcmr-fieldgt
• ltcmr-field-namegtidentitylt/cmr-field-namegt
  
• lt/cmr-fieldgt
• lt/ejb-relationship-rolegt

Matches void setIdentity(PersonLocal) PersonLocal
getIdentity() from EJB Class
8
Defining Person-gtBorrowerin ejb-jar.xml

• ltejb-relationship-rolegt
• ltejb-relationship-role-namegtIdentity-to-Borr
  owerlt/ejb-relationship-role-namegt
• ltmultiplicitygtOnelt/multiplicitygt
• ltrelationship-role-sourcegt
• ltejb-namegtPersonlt/ejb-namegt
• lt/relationship-role-sourcegt
• lt/ejb-relationship-rolegt
• lt/ejb-relationgt

Unidirectional choice signified by no cmr-field
in Person mapping back to Borrower
9
ejb-jar.xml

• Every Relationship must have a name
• Every ltejb-relationgt has exactly two
  ltejb-relationship-rolegt sub-elements defined
• ejb-relationship-role must define a cmr-field to
  be navigatable to the related object (otherwise
  unidirectional)

10
Stored in the Database

• create table Person (
• id varchar(12) not null unique,
• firstName varchar(32) not null,
• lastName varchar(32) not null,
• address varchar(128),
• phoneNumber char(10)
• )
• create table Borrower (
• id varchar(12) not null,
• beginDate date not null,
• endDate date,
• person_id char(12)
• )

11
Mapped to the Databaseby the Implementation

• weblogic-cmp-rdbms-jar.xml
• ltweblogic-rdbms-jargt
• ltweblogic-rdbms-beangt
• ...
• lt/weblogic-rdbms-beangt
• ltweblogic-rdbms-relationgt
• lt/weblogic-rdbms-relationgt
• ...
• ltcreate-default-dbms-tablesgtFalselt/create-defau
  lt-dbms-tablesgt
• lt/weblogic-rdbms-jargt

12
Mapped to the Databaseby the Implementation

• ltweblogic-rdbms-relationgt
• ltrelation-namegtBorrower-Personlt/relation-name
  gt
• ltweblogic-relationship-rolegt
• ltrelationship-role-namegtBorrower-to-Identi
  ty
• lt/relationship-role-namegt
• ltcolumn-mapgt
• ltforeign-key-columngtperson_idlt/foreign-
  key-columngt
• ltkey-columngtidlt/key-columngt
• lt/column-mapgt
• lt/weblogic-relationship-rolegt
• ltweblogic-relationship-rolegt
• ltrelationship-role-namegtIdentity-to-Borrow
  er
• lt/relationship-role-namegt
• lt/weblogic-relationship-rolegt
• lt/weblogic-rdbms-relationgt

names must match values specified in ejb-jar.xml
person_id is column in Borrower
id is column in Person
13
One-to-One Unidirectional
interface PersonLocal String getId()
String getFirstName() void setFirstName(String
fname) String getLastName() void
setLastName(String lname) String
getAddress() void setAddress(String
address) String getPhoneNumber() void
setPhoneNumber(String number)
interface BorrowerLocal String getId()
String getName() String getPhoneNumber()
String getAddress() Date getBeginDate()
Date getEndDate() boolean isValid() void
terminate()
1
0..1
table Person id varchar(12) not null unique,
firstName varchar(32) not null, lastName
varchar(32) not null, address varchar(128),
phoneNumber char(10)
table Borrower id varchar(12) not null,
beginDate date not null, endDate date,
person_id varchar(12)
1
0..1
14
One-to-One Unidirectional

• BorrowerEJB
• public abstract void setIdentity(PersonLocal
  person)
• public abstract PersonLocal getIdentity()
• ejb-jar.xml
• ltcmr-fieldgt
• ltcmr-field-namegtidentitylt/cmr-field-namegt
• lt/cmr-fieldgt
• weblogic-cmp-rdbms-jar.xml
• ltcolumn-mapgt
• ltforeign-key-columngtperson_idlt/foreign-
  key-columngt
• ltkey-columngtidlt/key-columngt
• lt/column-mapgt

15
Not Possible to Share Object from 11 Relation
aBorrower
xPerson
bBorrower
yPerson
PersonLocal x a.getIdentity() b.setIdentity(x)
aBorrower
xPerson
bBorrower
yPerson
16
One-to-One Bidirectional
interface PersonLocal String getId()
String getFirstName() void setFirstName(String
fname) String getLastName() void
setLastName(String lname) String
getAddress() void setAddress(String
address) String getPhoneNumber() void
setPhoneNumber(String number) Borrower
getBorrower()
interface BorrowerLocal String getId()
String getName() String getPhoneNumber()
String getAddress() Date getBeginDate()
Date getEndDate() boolean isValid() void
terminate()
1
0..1
table Person id varchar(12) not null unique,
firstName varchar(32) not null, lastName
varchar(32) not null, address varchar(128),
phoneNumber char(10)
table Borrower id varchar(12) not null,
beginDate date not null, endDate date,
person_id varchar(12)
1
0..1
17
One-to-One Bidirectional

• BorrowerEJB
• public abstract void setIdentity(PersonLocal
  person)
• public abstract PersonLocal getIdentity()
• PersonEJB
• public abstract void setBorrower(BorrowerLocal
  person)
• public abstract BorrowerLocal getBorrower ()
• ejb-jar.xml
• ltcmr-fieldgt //from borrower to person
• ltcmr-field-namegtidentitylt/cmr-field-namegt
• lt/cmr-fieldgt
• ltcmr-fieldgt //from person to borrower
• ltcmr-field-namegtborrowerlt/cmr-field-namegt
• lt/cmr-fieldgt
• Note!!! - bidirectional and unidirectional
  database schema is identical. Only EJB class and
  portions of the deployment descriptor changed

18
One-to-One Bidirectional (cont.)

• weblogic-cmp-rdbms-jar.xml
• ltcolumn-mapgt //from borrower to person
• ltforeign-key-columngtperson_idlt/foreign-
  key-columngt
• ltkey-columngtidlt/key-columngt
• lt/column-mapgt

19
Not Possible to Share Object from 11 Relation
aBorrower
xPerson
bBorrower
yPerson
PersonLocal x a.getIdentity() b.setIdentity(x)
aBorrower
xPerson
bBorrower
yPerson
20
One-to-Many Bidirectional
interface BorrowerLocal Set getCheckouts()
Date getBeginDate() Date getEndDate()
boolean isValid() void terminate()
interface CheckoutLocal Integer getId()
Date getOutDate() boolean isOverdue()
BorrowerLocal getBorrower()

1
table Checkout id int not null unique,
outDate longint not null, borrower_id
varchar(12)
table Borrower id varchar(12) not null,
beginDate date not null, endDate date,
person_id varchar(12)

1
21
One-to-Many Bidirectional

• BorrowerEJB
• public abstract void setCheckouts(Set
  checkouts)
• public abstract Set getCheckouts()
• public void addCheckout(CheckoutLocal
  checkout) throws CheckoutException
• getCheckouts().add(checkout)
• java.util.Collection and Set are only allowable
  CMR-many data types
• Collection allowed to have duplicates
• Set not allowed to have duplicates
• CheckoutEJB
• public abstract void setBorrower(BorrowerLocal
  borrower)
• public abstract BorrowerLocal getBorrower()

22
One-to-Many Bidirectional (cont.)

• ejb-jar.xml
• ltmultiplicitygtOnelt/multiplicitygt
• ltcmr-fieldgt
• ltcmr-field-namegtcheckoutslt/cmr-field-name
  gt
• ltcmr-field-typegtjava.util.Setlt/cmr-field-
  typegt
• lt/cmr-fieldgt
• ltmultiplicitygtManylt/multiplicitygt
• ltcmr-fieldgt
• ltcmr-field-namegtborrowerlt/cmr-field-namegt
• lt/cmr-fieldgt
• weblogic-cmp-rdbms-jar.xml
• ltcolumn-mapgt
• ltforeign-key-columngtborrower_idlt/foreig
  n-key-columngt
• ltkey-columngtidlt/key-columngt
• lt/column-mapgt

23
Not Possible to Share Object from 1N Relation
aBorrower
xCheckout
yCheckout
bBorrower
zCheckout
Collection checkouts a.getCheckouts() b.setChec
kouts(checkouts)
aBorrower
xCheckout
yCheckout
bBorrower
zCheckout
24
Not Possible to Share Object from 1N Relation
aBorrower
xCheckout
yCheckout
bBorrower
zCheckout
BorrowerLocal b z.getBorrower() y.setBorrower(b
)
aBorrower
xCheckout
yCheckout
bBorrower
zCheckout
25
Iterating the Many Collection

• for(java.util.Iterator igetCheckouts().iterator()
  i.hasNext() ) CheckoutLocal co
  (CheckoutLocal)i.next()//use co
• Must not add/remove elements from collection
  while using iterator
• only exception is use of i.remove()
• Empty collections are returned for no elements

26
Many-to-Many Unidirectional
interface TopicLocal String getId() String
getTitle() Collection getAuthors() void
addAuthor(PersonLocal authors)
interface PersonLocal String getId()
String getFirstName()


table Topic id char(6) not null unique,
title varchar(32) not null,
1

table PersonTopicLink topic_id char(6) not
null, person_id char(6) not null

table Person id char(6) not null unique,
firstName varchar(32)
1
Use Linking Table for NN or linking legacy
tables together
27
Many-to-Many Unidirectional

• TopicEJB
• public abstract void setAuthors(Collection
  authors)
• public abstract Collection getAuthors()
• public void addAuthor(PersonLocal author)
• getAuthors().add(author)
• ejb-jar.xml
• ltmultiplicitygtManylt/multiplicitygt
• ltcmr-fieldgt
• ltcmr-field-namegtauthorslt/cmr-field-namegt
• ltcmr-field-typegtjava.util.Collectionlt/cmr
  -field-typegt
• lt/cmr-fieldgt
• ltmultiplicitygtManylt/multiplicitygt

28
Many-to-Many Unidirectional (cont.)

• weblogic-cmp-rdbms-jar.xml
• lttable-namegtPersonTopicLinklt/table-namegt
• ltcolumn-mapgt //from link to person table
• ltforeign-key-columngtperson_idlt/foreign-
  key-columngt
• ltkey-columngtidlt/key-columngt
• lt/column-mapgt
• ltcolumn-mapgt //from link to topic table
• ltforeign-key-columngttopic_idlt/foreign-k
  ey-columngt
• ltkey-columngtidlt/key-columngt
• lt/column-mapgt

29
Objects Sharable in NN Relation
aTopic
xPerson
yPerson
bTopic
zPerson
Collection authors a.getAuthors() b.setAuthors(
authors)
aTopic
xPerson
yPerson
bTopic
zPerson
30
Objects Sharable in NN Relation
aTopic
xPerson
yPerson
bTopic
zPerson
PersonLocal x a.getAuthorByName(x) b.addAutho
r(x)
aTopic
xPerson
yPerson
bTopic
zPerson
31
Cascade Delete

• Causes the delete of one or more objects when a
  related object is deleted
• Used with one-to-one and one-to-many
  relationships
• entity bean that causes the cascade delete must
  have a multiplicity of one
• Implementation be deferred to database by
  container

32
Defining Cascade Deletein ejb-jar.xml

• ltrelationshipsgt
• ltejb-relationgt lt!-- Borrower(0..1)-gt(1)Perso
  n (unidirectional) --gt
• ltejb-relation-namegtBorrower-Personlt/ejb-r
  elation-namegt
• ltejb-relationship-rolegt
• ltejb-relationship-role-namegtBorrower-t
  o-Identity
• lt/ejb-relationship-role-namegt
• ltmultiplicitygtOnelt/multiplicitygt
• ltcascade-delete/gt lt!-- delete
  Borrower role when delete Person --gt
• ltrelationship-role-sourcegt
• ltejb-namegtBorrowerlt/ejb-namegt
• lt/relationship-role-sourcegt
• ltcmr-fieldgt
• ltcmr-field-namegtidentitylt/cmr-field
  -namegt
• lt/cmr-fieldgt
• lt/ejb-relationship-rolegt