CMP Persistence (1:n Relations)

Thread view:

ralf sczepan - 20 Oct 2003 11:12 GMT

Hi Group,
I have got two Entity-Beans, one is named Product the other ist named
ProductGroup. I would like to implement a 1:n Relation wich means
every Product has one Productgroup and a Productgroup has many
Products.

The ProductGroupBean.java looks like this:
........
public abstract class ProductGroupBean implements EntityBean{
protected EntityContext ctx;

public abstract Integer getId() ;
public abstract void setId(Integer id);
public abstract Collection getProduct();
public abstract void setProduct(Collection artikel);
......

In the Client I try set an Product in a ProductGroupBean

.......
ProductHome productHome =
(ProductHome)javax.rmi.PortableRemoteObject.narrow(obj,
ProductHome.class );
Product product = productHome.create(new Integer(1183),
"Book", "j", "status", new Integer(1));

Object objg = ctx.lookup( "ProductGroup" );
ProductGroupHome productGroupHome =
ProductGroupHome)javax.rmi.PortableRemoteObject.narrow(objg,
ProductGroupHome.class );
ProductGroup productGroup = productGroupHome.create( new Integer(43),
"Media");

Collection artikels = new ArrayList();
artikels.add(artikel);

artikelgruppe.setArtikel(artikels); //<-- This method causes a
ClassCastException
........

Whats wrong with this method? I can not sea any reason for this
Exception!
Or isn't it the way to use Collection in 1:n RelationShips whith
Beans?

Thanks for your help

Reply to this Message

Marek Lange - 20 Oct 2003 11:53 GMT

> Hi Group,
> I have got two Entity-Beans, one is named Product the other ist named
[quoted text clipped - 32 lines]
> Collection artikels = new ArrayList();
> artikels.add(artikel);

^^^^^^^^ is this your product created above?

>
> artikelgruppe.setArtikel(artikels); //<-- This method causes a
[quoted text clipped - 4 lines]
> Or isn't it the way to use Collection in 1:n RelationShips whith
> Beans?

I always used this way (adapted to your example):

Collection artikels = artikelGruppe.getArtikel();

// should be enough to set the relation
artikels.add(artikel);

Post more code if this does not work.

-marek

Reply to this Message

ralf sczepan - 21 Oct 2003 15:32 GMT

> >
> > Collection artikels = new ArrayList();
> > artikels.add(artikel);
> ^^^^^^^^ is this your product created above?

Yes that is the Product! (I "translated" the Source from German to
English and forgot some parts, sorry)

> I always used this way (adapted to your example):
>
[quoted text clipped - 6 lines]
>
> -marek

first of all thanks for help

If I use this Code in a SessionBean (means I use the Local -
Interfaces) it works. But I get an Exception if I try to get the
Collection filled with Artikels.

Collection artikels = artikelGruppe.getArtikel(); // throws an
Exception

Here some more Code:

public abstract class ArtikelBean implements EntityBean {
protected EntityContext ctx;
public abstract Integer getArtid();
public abstract void setArtid(Integer id);
public abstract String getBezeichnung();
public abstract void setBezeichnung(String name);

public abstract Collection getArtikelGruppe();
public abstract void setArtikelGruppe(Collection artgruppen);
public void setEntityContext (EntityContext ctx) {
this.ctx = ctx;
}
....

}

public interface Artikel extends EJBObject {
public Integer getArtid() throws RemoteException;
public void setArtid(Integer id) throws RemoteException;
public String getBezeichnung() throws RemoteException;
public void setBezeichnung(String bez) throws RemoteException;

public Collection getArtikelGruppe() throws RemoteException;
public void setArtikelGruppe(Collection artgruppen) throws
RemoteException;
}

The ejb-jar.xml

<?xml version="1.0"?>

<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise
JavaBeans 2.0//EN" "http://java.sun.com/dtd/ejb-jar_2_0.dtd">

<ejb-jar>
<enterprise-beans>

<entity>
<ejb-name>Artikel</ejb-name>
<home>satzmedia.sGrid.app.model.ArtikelHome</home>
<remote>satzmedia.sGrid.app.model.Artikel</remote>
<local-home>satzmedia.sGrid.app.model.ArtikelLocalHome</local-home>
<local>satzmedia.sGrid.app.model.ArtikelLocal</local>
<ejb-class>satzmedia.sGrid.app.model.ArtikelBean</ejb-class>
<persistence-type>Container</persistence-type>
<prim-key-class>java.lang.Integer</prim-key-class>
<reentrant>False</reentrant>
<cmp-version>2.x</cmp-version>
<abstract-schema-name>ArtikelBean </abstract-schema-name>
<cmp-field><field-name>artid</field-name></cmp-field>
<cmp-field><field-name>bezeichnung</field-name></cmp-field>
<primkey-field>artid</primkey-field>
<query>
<query-method>
<method-name>findByBezeichnung</method-name>
<method-params>
<method-param>java.lang.String</method-param>
</method-params>
</query-method>
<ejb-ql>
<![CDATA[SELECT OBJECT(a) FROM ArtikelBean AS a where
a.bezeichnung = ?1]]>
</ejb-ql>
</query>
</entity>
<entity>
<ejb-name>ArtikelGruppe</ejb-name>
<home>satzmedia.sGrid.app.model.ArtikelGruppeHome</home>
<remote>satzmedia.sGrid.app.model.ArtikelGruppe</remote>
<local-home>satzmedia.sGrid.app.model.ArtikelGruppeLocalHome</local-home>
<local>satzmedia.sGrid.app.model.ArtikelGruppeLocal</local>
<ejb-class>satzmedia.sGrid.app.model.ArtikelGruppeBean</ejb-class>
<persistence-type>Container</persistence-type>
<prim-key-class>java.lang.Integer</prim-key-class>
<reentrant>False</reentrant>
<cmp-version>2.x</cmp-version>
<abstract-schema-name>ArtikelGruppeBean</abstract-schema-name>
<cmp-field><field-name>id</field-name></cmp-field>
<cmp-field><field-name>bezeichnung</field-name></cmp-field>
<primkey-field>id</primkey-field>
<query>
<query-method>
<method-name>findByBezeichnung</method-name>
<method-params>
<method-param>java.lang.String</method-param>
</method-params>
</query-method>
<ejb-ql>
<![CDATA[SELECT OBJECT(a) FROM ArtikelGruppeBean AS a
where a.bezeichnung = ?1]]>
</ejb-ql>
</query>
</entity>
</enterprise-beans>

<relationships>
<ejb-relation>

<ejb-relation-name>Artikel-ArtikelGruppe</ejb-relation-name>
<ejb-relationship-role>
<ejb-relationship-role-name>
Artikel haben ArtikelGruppen
</ejb-relationship-role-name>
<multiplicity>Many</multiplicity>
<relationship-role-source>
<ejb-name>Artikel</ejb-name>
</relationship-role-source>
<cmr-field>

<cmr-field-name>ArtikelGruppe</cmr-field-name>

<cmr-field-type>java.util.Collection</cmr-field-type>
</cmr-field>
</ejb-relationship-role>
<ejb-relationship-role>
<ejb-relationship-role-name>
Artikelgruppen haben Artikel
</ejb-relationship-role-name>
<multiplicity>Many</multiplicity>
<relationship-role-source>

<ejb-name>ArtikelGruppe</ejb-name>
</relationship-role-source>
<cmr-field>

<cmr-field-name>Artikel</cmr-field-name>

<cmr-field-type>java.util.Collection</cmr-field-type>
</cmr-field>
</ejb-relationship-role>
</ejb-relation>
</relationships>
</ejb-jar

Reply to this Message

Marek Lange - 22 Oct 2003 19:45 GMT

ralf sczepan schrieb:

> If I use this Code in a SessionBean (means I use the Local -
> Interfaces) it works. But I get an Exception if I try to get the
> Collection filled with Artikels.

I saw your posting in d.c.l.j. See my comments on bean design please.

> public abstract class ArtikelBean implements EntityBean {
> protected EntityContext ctx;
[quoted text clipped - 8 lines]
> this.ctx = ctx;
> }

Looks good.

> public interface Artikel extends EJBObject {
> public Integer getArtid() throws RemoteException;
[quoted text clipped - 6 lines]
> RemoteException;
> }

I assume from this that you are using a remote interface for your Entity
Beans? Please try to change to local interfaces. Accessing an entity
remotely is poor design.

> The ejb-jar.xml

Nothing seems to be wrong in your descriptor. I can't explain the
ClassCastException so far.

-marek

Reply to this Message

CMP Persistence (1:n Relations)

Free Magazines