I'm a CMP fanatic too :) But keep in mind some of us have to deal with
existing models that have been created in the
"traditionnal" RDBMS fashion. It's good to have control on the way CMP
will work with Orion.
We have solved the O-R mapping problem by having a code generator
generate first-cut beans from the database. Then
we use a heavily modified version of Rickard Öberg's java doclet to
generate the home interface, the remote interface
a data structure for quick access to data, the ejb-jar.xml AND
orion-ejb-jar.xml which allows fine-grained control on
the tables and attributes used for the mapping through the use of
javadoc tags.
For example, all CMP fields are marked with the tag @cmp-field. a
@cmp-table tag will indicate (through the orion-ejb-jar.xml file)
what underlying table is needed for the bean. Similarly @cmp-attribute
indicates the doclet what underlying attribute we are
mapping to. 1-N and N-M relationships are also supported through doclet
tags.
This allows a quick regeneration of all source files from one master
bean source file. It also enables, through modifications to the
doclet, generating other vendor specific files like jboss.xml,
inprise-ejb.xml etc.
As a bonus, the doclet generates a façade object that allows a connected
(via remote methods) or disconnected
(via the data object) view of an entity's data.
This was a little off-topic, but the point I'm trying to make is that
when existing schemas are used, some knowledge on the
mapping process can help.
Cheers
-----Message d'origine-----
De : Magnus Rydin [mailto:[EMAIL PROTECTED]]
Envoyé : 23 janvier, 2001 08:51
À : Orion-Interest
Objet : SV: O/R mapping
One of the things I like best with EJB is that I dont have to care about
how my objects are stored (Yes, im a CMP fanatic).
So my personal contribution to the subject must be:
who cares how many tables are used 'back there' ? :)
> -----Ursprungligt meddelande-----
> Från: Daniel Cardin [ mailto:[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> ]
> Skickat: den 23 januari 2001 05:01
> Till: Orion-Interest
> Ämne: RE: O/R mapping
>
>
> I'd like to point out that a third table is only needed for a N-M
> (many-to-many) relationship.
> In the case of a 1-N relationship, simply have a foreign key to the
> master table.
>
> For example :
>
> Customer object refers to a Country object
> you a Customer will only have one Country object. you do NOT need a
> third table to map this.
> Simply add a field in Customer that contains the foreign key to the
> Country object.
>
> The EJB 2.0 mapping is Simple
>
>
>
> Customer ...
>
> public abstract Country getCountry();
> public abstract void setCountry(Country aCountry);
>
> and in Country
>
> public abstract Collection getCustomers();
> public abstract void setCustomer(Collection customers);
>
> This is fully supported by Orion, which will populate the collection
> object automatically.
>
> Cheers,
>
> Daniel
>
>
> -----Message d'origine-----
> De : Tony J Brooks [ mailto:[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> ]
> Envoyé : 22 janvier, 2001 11:27
> À : Orion-Interest
> Objet : RE: O/R mapping
>
>
>
> Hi Theis,
>
> As much as I can remember, there *is* - definitely - a need for an
> intermediate third table to contain the mapping information. By using
> this
> third table, you eliminate data replication/redundancy in the
> other two
> tables.
>
> To my knowledge this is a common technique. ER tools typically create
> such
> an intermediate table for you when you select a relationship to be
> 'zero/one/many to many'. Whether you see that on your diagram is
> another
> matter, but you will definitely see it in your DB ;)
>
> Apologies if I have misunderstood your question.
>
> Bye for now,
> Tony.
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [ mailto:[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> ]On Behalf Of
> [EMAIL PROTECTED]
> Sent: 22 January 2001 15:10
> To: Orion-Interest
> Subject: O/R mapping
>
>
> Hi!
>
> I have been reading the complex-or example and ploughed
> through the atm
> example. In the complex-or example it is stated that collections are
> mapped
> to an another table and that the reason for this is normalization. The
> Atm
> example is also following this principle.
>
> Is this really correct? I have never seen the necessity for mapping
> anone
> to many relation to a third table (even though it was a long
> time ago I
> read the rules of normalization I'm very doubtful that this
> is correct).
> Could someone tell me the rational behind this.
>
> If this not true, how does the xml look like (in the
> orion-ejb-jar.xml)
> when you only map the relation as a foreign key?
>
> Regards
>
> /Theis
>
>
>
>
