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Posted to ojb-user@db.apache.org by Michael Duffy <du...@yahoo.com> on 2003/03/17 22:56:21 UTC
Adding A New Component With A 1:1 Relationship
I have a newbie question, if you don't mind.
Your advanced O/R tutorial shows a 1:1 mapping example
with Article and ProductGroup classes. You've shown
the table schemas (in German, but I follow you) and
the repository_user.xml. All very good, of course.
The repository XML for Article has a productGroupId
that points to the ProductGroup key, and an instance
of ProductGroup that is supposed to be owned by the
Article.
Now if I want to ask the broker to store a brand new
Article, how do I do it? Is the productGroupId
required to be set to an existing before I call
broker.store(newArticle)? If I want to have a new
ProductGroup for my Article, do I have to do this as a
five-step transaction?
1. Create a new ProductGroup instance
2. Store the new ProductGroup instance
3. Get the latest ProductGroup instances's primary key
4. Create a new Article, using the PG primary key
5. Store the new Article
I'm sure it's my lack of understanding, because this
feels very difficult. I'm still climbing that OJB
learning curve.
Thank you for your work, help, and patience.
Sincerely, MOD
__________________________________________________
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Re: Adding A New Component With A 1:1 Relationship
Posted by Michael Duffy <du...@yahoo.com>.
Thomas,
Of course you're correct. I'd added foreign key
constraints to all my tables. Once I removed them,
OJB did the INSERT and managed all the keys for me, as
you said. I apologize for missing that subtlety.
Should I also remove foreign key constraints on
many-to-many tables? I've got three of them in this
schema. Will OJB handle those as nicely as the 1:1?
"...I agree, there is a learning curve with OJB. O/R
mapping is not trivial. But it is worth the effort.
Once you mastered the learning curve you will ask
yourself, how could I write database applications
without an O/R tool?..." - I totally agree with this
statement. That's why I'm persisting with OJB, even
if it makes me nervous about my release date.
IMHO, two great benefits of an object/relational
mapping layer are that they force SQL code out of the
business objects and they allow CMP without entity
EJBs. You can write J2EE without an app server; J2EE
and EJB need not be synonymous.
Thank you again for your fine work and timely advice.
Sincerely, MOD
--- Thomas Mahler <th...@web.de> wrote:
> Hi Michael,
>
> Michael Duffy wrote:
> > I have a newbie question, if you don't mind.
> >
> > Your advanced O/R tutorial shows a 1:1 mapping
> example
> > with Article and ProductGroup classes. You've
> shown
> > the table schemas (in German, but I follow you)
> and
> > the repository_user.xml. All very good, of
> course.
> >
> > The repository XML for Article has a
> productGroupId
> > that points to the ProductGroup key, and an
> instance
> > of ProductGroup that is supposed to be owned by
> the
> > Article.
> >
> > Now if I want to ask the broker to store a brand
> new
> > Article, how do I do it? Is the productGroupId
> > required to be set to an existing before I call
> > broker.store(newArticle)?
>
> Depends on the database. If there is a FK constraint
> then yes.
> But as you can see from the table schema, there are
> no formal FK
> constraints. So, the productGroupId needs not to be
> filled.
>
> > If I want to have a new
> > ProductGroup for my Article, do I have to do this
> as a
> > five-step transaction?
> >
> > 1. Create a new ProductGroup instance
> > 2. Store the new ProductGroup instance
> > 3. Get the latest ProductGroup instances's primary
> key
> > 4. Create a new Article, using the PG primary key
> > 5. Store the new Article
>
> No it's much easier, as OJB takes care of FK
> assigment automatically:
> 1. Create a new Article a
> 2. Create a new ProductGroup instance pg
> 3. call a.setProductGroup(pg)
> 4. store the new Article.
>
> OJB manages the FK assignment for you. If you have
> set
> auto-update="true" on the productGroup
> reference-descriptor then OJB
> will also store the new PG on storing the new
> article!
>
>
> > I'm sure it's my lack of understanding, because
> this
> > feels very difficult. I'm still climbing that OJB
> > learning curve.
>
> I agree, there is a learning curve with OJB. O/R
> mapping is not trivial.
> But it is worth the effort. Once you mastered the
> learning curve you
> will ask yourself, how could I write database
> applications without an
> O/R tool?
>
> cheers,
> Thomas
>
> >
> > Thank you for your work, help, and patience.
> > Sincerely, MOD
> >
> >
> > __________________________________________________
> > Do you Yahoo!?
> > Yahoo! Platinum - Watch CBS' NCAA March Madness,
> live on your desktop!
> > http://platinum.yahoo.com
> >
> >
>
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__________________________________________________
Do you Yahoo!?
Yahoo! Platinum - Watch CBS' NCAA March Madness, live on your desktop!
http://platinum.yahoo.com
Re: Adding A New Component With A 1:1 Relationship
Posted by Thomas Mahler <th...@web.de>.
Hi Michael,
Michael Duffy wrote:
> I have a newbie question, if you don't mind.
>
> Your advanced O/R tutorial shows a 1:1 mapping example
> with Article and ProductGroup classes. You've shown
> the table schemas (in German, but I follow you) and
> the repository_user.xml. All very good, of course.
>
> The repository XML for Article has a productGroupId
> that points to the ProductGroup key, and an instance
> of ProductGroup that is supposed to be owned by the
> Article.
>
> Now if I want to ask the broker to store a brand new
> Article, how do I do it? Is the productGroupId
> required to be set to an existing before I call
> broker.store(newArticle)?
Depends on the database. If there is a FK constraint then yes.
But as you can see from the table schema, there are no formal FK
constraints. So, the productGroupId needs not to be filled.
> If I want to have a new
> ProductGroup for my Article, do I have to do this as a
> five-step transaction?
>
> 1. Create a new ProductGroup instance
> 2. Store the new ProductGroup instance
> 3. Get the latest ProductGroup instances's primary key
> 4. Create a new Article, using the PG primary key
> 5. Store the new Article
No it's much easier, as OJB takes care of FK assigment automatically:
1. Create a new Article a
2. Create a new ProductGroup instance pg
3. call a.setProductGroup(pg)
4. store the new Article.
OJB manages the FK assignment for you. If you have set
auto-update="true" on the productGroup reference-descriptor then OJB
will also store the new PG on storing the new article!
> I'm sure it's my lack of understanding, because this
> feels very difficult. I'm still climbing that OJB
> learning curve.
I agree, there is a learning curve with OJB. O/R mapping is not trivial.
But it is worth the effort. Once you mastered the learning curve you
will ask yourself, how could I write database applications without an
O/R tool?
cheers,
Thomas
>
> Thank you for your work, help, and patience.
> Sincerely, MOD
>
>
> __________________________________________________
> Do you Yahoo!?
> Yahoo! Platinum - Watch CBS' NCAA March Madness, live on your desktop!
> http://platinum.yahoo.com
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: ojb-user-unsubscribe@db.apache.org
> For additional commands, e-mail: ojb-user-help@db.apache.org
>
>