I sure am glad that my car runs without my having to understand every screw
in the engine, or how a carburator works. But I still do care whether it
uses 8 or 12 litres of gas per 100 km. I think a superfluous associative
table fits this picture quite well.
----- Original Message -----
From: "Magnus Rydin" <[EMAIL PROTECTED]>
To: "Orion-Interest" <[EMAIL PROTECTED]>
Sent: Tuesday, January 23, 2001 2:51 PM
Subject: 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]]
> 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]]
> 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]]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
>
>
>
>
