In the Java code, we continue as usual:
- The BookBean is created as usual, the CMR authors field is set in the
ejbPostCreate()method - The same holds for the AuthorBean
Finally, for the sake of completeness, we illustrate how to access the authors from the book.
private BookDTO getBookData(BibliographyLocal bib)
{
BookDTO dto = new BookDTO();
// Book specifics
Collection authors = bib.getBook().getAuthorOReditors();
AuthorDTO[] authorsOReditors = new AuthorDTO[authors.size()];
Iterator iterator = authors.iterator();
int i = 0;
while (iterator.hasNext())
{
authorsOReditors[i] = getAuthorDTO(
(AuthorLocal) iterator.next());
i++;
}
...
(The Book Data Transfer Object BookDTO transfers the Book data retrieved from the Book entity bean (via a Session Facade) to the Web tier (or Java client)).
Via the BookLocal object, we have access to the collection of AuthorLocal objects, as shown above. Using the an interator we can access the individual Author objects, from which we can invoke the getters to retrieve the author information.
I’ve been trying to deploy a one to many relationship for two whole, I mean WHOLE days. ( I have to admit I did sleep), but no luck. Here is my code. I would appreciate your help.
I’m using the current maxdb, jboss-3.2.1. I’m sure I am doing something really wrong that is not obvious to me. One of the things that I noticed is that ejb-jar.xml does not have the key-field auto generated.
/*
* Created on Dec 29, 2005
*
* To change the template for this generated file go to
* Window>Preferences>Java>Code Generation>Code and Comments
*/
package ejb;
import javax.ejb.EntityBean;
import javax.ejb.EntityContext;
import java.util.Collection;
/**
* @ejb.bean name=”A”
* jndi-name=”ABean”
* type=”CMP”
* primkey-field=”a_id”
* schema=”a”
* cmp-version=”2.x”
*
*–
* This is needed for JOnAS.
* If you are not using JOnAS you can safely remove the tags below.
* @jonas.bean ejb-name=”A”
* jndi-name=”ABean”
* @jonas.jdbc-mapping jndi-name=”java:/SapdbDS” jdbc-table-name=”a”
* —
*
* @ejb.persistence
* table-name=”a”
*
* @ejb.finder
* query=”SELECT OBJECT(a) FROM a as a”
* signature=”java.util.Collection findAll()”
*–
* This is needed for JOnAS.
* If you are not using JOnAS you can safely remove the tags below.
* @jonas.finder-method-jdbc-mapping method-name=”findAll”
* jdbc-where-clause=””
* @jonas.jdbc-mapping jndi-name=”java:/SapdbDS”
* jdbc-table-name=”a”
*
*–
*
**/
public abstract class ABean implements EntityBean {
protected EntityContext ctx = null;
// business methods
/* public void addB() {
BLocal b = null;
try {
InitialContext BContext = new InitialContext( );
BLocalHome bHome = (BLocalHome)
BContext.lookup(“java:comp/env/ejb/B”);
b = bHome.create(getId());
} catch (Exception e) {
System.out.println(“exception @ BContext”);
}
Collection bCollection = this.getBBean( );
bCollection.add(b);
}
*/
/**
* CMR Collection containing bbean information
*
* @ return the bbean
*
*
* @ejb.interface-method
*
* @ejb.relation
* name=”a-refers-to-b”
* role-name=”aTob”
* target-ejb=”B”
* target-role-name=”bToa”
*
* @jboss.relation-mapping
* style=”relation-table”
*
* @jboss.relation-table
* table-name=”b”
* create-table=”false”
* remove-table=”false”
*
*@jboss.relation
* related-pk-field=”b_id”
* fk-column=”a_id_fk”
* fk-constraint=”false”
*/
public abstract Collection getBidfk();
/**
*
* @param java.util.Set the new b_id_fk value
*
* @ejb.interface-method
*
*
*/
public abstract void setBidfk(Collection b);
public void setEntityContext(EntityContext ctx) {
this.ctx = ctx;
}
public void unsetEntityContext() {
this.ctx = null;
}
/**
* The ejbCreate method.
*
* @ejb.create-method
*/
public java.lang.Long ejbCreate(Collection b) throws javax.ejb.CreateException {
setAid(new Long(0));
try {
BLocalHome bLocalHome = BUtil.getLocalHome();
java.util.Iterator it = b.iterator();
while (it.hasNext()) {
bLocalHome.create(getAid());
}
} catch (Exception e) {
System.out.println(“a.ejbCreate”);
System.out.println(e.getStackTrace());
}
return null;
}
/**
* The container invokes this method immediately after it calls ejbCreate.
*
*/
public void ejbPostCreate(Collection b) throws javax.ejb.CreateException {
try {
BLocalHome bLocalHome = BUtil.getLocalHome();
setBidfk(bLocalHome.findByForeignKey(getAid()));
} catch (Exception e) {
System.out.println(“a.ejbPostCreate”);
System.out.println(e.getStackTrace());
}
}
/**
* Returns the a_id
* @return the a_id
*
* @ejb.persistent-field
* @ejb.persistence
* column-name=”a_id”
* sql-type=”fixed(10)”
* @ejb.pk-field
* @ejb.interface-method
*
* —
* This is needed for JOnAS.
* If you are not using JOnAS you can safely remove the tags below.
* @jonas.cmp-field-jdbc-mapping field-name=”a_id”
* jdbc-field-name=”a_id”
*
—
*/
public abstract java.lang.Long getA_id();
/**
* Sets the a_id
*
* @param java.lang.Long the new a_id value
*
* @ejb.interface-method
*/
public abstract void setA_id(java.lang.Long a_id);
}
/*
* Created on Dec 29, 2005
*
* To change the template for this generated file go to
* Window>Preferences>Java>Code Generation>Code and Comments
*/
package ejb;
import javax.ejb.EntityBean;
import javax.ejb.EntityContext;
import java.lang.Long;
/**
* @ejb.bean name=”B”
* jndi-name=”BBean”
* type=”CMP”
* primkey-field=”b_id”
* schema=”b”
* cmp-version=”2.x”
*
*–
* This is needed for JOnAS.
* If you are not using JOnAS you can safely remove the tags below.
* @jonas.bean ejb-name=”B”
* jndi-name=”BBean”
* @jonas.jdbc-mapping jndi-name=”java:/SapdbDS” jdbc-table-name=”b”
* —
*
* @ejb.persistence
* table-name=”b”
*
* @ejb.finder
* query=”SELECT OBJECT(a) FROM b as a”
* signature=”java.util.Collection findAll()”
*
* @ejb.finder
* query=”SELECT OBJECT(a) FROM a as a WHERE a_id_fk=?1″
* signature=”java.util.Collection findByForeignKey(java.lang.Long a)”
*–
* This is needed for JOnAS.
* If you are not using JOnAS you can safely remove the tags below.
* @jonas.finder-method-jdbc-mapping method-name=”findAll”
* jdbc-where-clause=””
* @jonas.jdbc-mapping jndi-name=”java:/SapdbDS”
* jdbc-table-name=”b”
*
*–
*
**/
public abstract class BBean implements EntityBean {
/* public abstract ALocal getABean();
public abstract void setABean(ALocal abean);
*/
protected EntityContext ctx = null;
public void setEntityContext(EntityContext ctx) {
this.ctx = ctx;
}
public void unsetEntityContext() {
this.ctx = null;
}
/**
* The ejbCreate method.
*
* @ejb.create-method
*/
public java.lang.Long ejbCreate(Long a_id_fk) throws javax.ejb.CreateException {
setB_id(new Long(0));
setAidfk(a_id_fk);
return null;
}
/**
* The container invokes this method immediately after it calls ejbCreate.
*
*/
public void ejbPostCreate() throws javax.ejb.CreateException {
}
/**
* Returns the b_id
* @return the b_id
*
* @ejb.persistent-field
* @ejb.persistence
* column-name=”b_id”
* sql-type=”fixed(10)”
* @ejb.pk-field
* @ejb.interface-method
*
* —
* This is needed for JOnAS.
* If you are not using JOnAS you can safely remove the tags below.
* @jonas.cmp-field-jdbc-mapping field-name=”b_id”
* jdbc-field-name=”b_id”
*
—
*/
public abstract java.lang.Long getB_id();
/**
* Sets the b_id
*
* @param java.lang.Long the new b_id value
*
* @ejb.interface-method
*/
public abstract void setB_id(java.lang.Long b_id);
/**
* Returns the a_id_fk
* @return the a_id_fk
*
* @ejb.persistent-field
* @ejb.persistence
* column-name=”a_id_fk”
* sql-type=”fixed(10)”
*
* @ejb.interface-method
*
* —
* This is needed for JOnAS.
* If you are not using JOnAS you can safely remove the tags below.
* @jonas.cmp-field-jdbc-mapping field-name=”a_id_fk”
* jdbc-field-name=”a_id_fk”
*
—
*/
public abstract java.lang.Long getAidfk();
/**
* Sets the a_id_fk
*
* @param java.lang.Long the new a_id_fk value
*
* @ejb.interface-method
*/
public abstract void setAidfk(java.lang.Long aidfk);
}
Generated by XDoclet
markup for those beans.
–>
B
ejb.BHome
ejb.B
ejb.BLocalHome
ejb.BLocal
ejb.BCMP
Container
java.lang.Long
False
2.x
b
b_id
aidfk
b_id
findAll
findByForeignKey
java.lang.Long
A
ejb.AHome
ejb.A
ejb.ALocalHome
ejb.ALocal
ejb.ACMP
Container
java.lang.Long
False
2.x
a
a_id
a_id
findAll
markup for those beans.
–>
markup for those beans.
–>
a-refers-to-b
aTob
One
A
bidfk
java.util.Collection
bToa
Many
B
markup.
–>
I’m afraid not, but there is a comprehensive post on a uni-directional one-to-one relationship, see this post. Combining the information of these two posts, you should have enough information to get your specific case up and running without too much effort.
Is there an article on uni-directonal one-to-many relationships anywhere on this site
I never implemented a case where you want to have an additional column in the link table. I’m afraid that you cannot make use of this "implicit table definition mechanism" anymore. However, you can always define your link table as a separate entity bean with the proper relations, of course, including additional columns.
I’m not quite sure though what you mean with the registry, but hopefully this answer suffices already.
Hi
This article is very clear, but I have a question: What if I need to
have another column in the “relation table”? A different column related
with the registry….
Thanks for your help.