|
I don't think this will
work unless you are willing to lock the entire table before you execute
this. Otherwise, you will have a race condition for the unique
key.
Jim
Ralph,
Just to add that the autoincrement needn't be database
specific... your ejb could just have
keyValue = keyValue+1;
where keyValue maps to the underlying column in the database
table.
That way autoincrement is not database specific! If you want to use to
the database specific primary key generation you could do so.
regards.
Vinay
----- Original Message -----
From: Ralph
Jensen
Sent: Friday, May 04, 2001 1:09
PM
To: [EMAIL PROTECTED]
Subject: Re: [JBoss-user] EJB
question
Thanks. But that is actually much more than I want. I only
need a unique
INT for primary keys.
For the moment I will try
this:
In the sql-script:
create table
uniqueInteger(
pk INTEGER constraint pk_unique primary
key,
uniqueID INTEGER
);
insert into
uniqueInteger VALUES( 1, 1 );
Then in the bean:
SELECT
uniqueID from uniqeInteger;
save uniqueID in variable ( let's call it
'uniqueVar' )
then:
UPDATE uniqueInteger SET uniqueID =
uniqueVar+1 WHERE pk = 1;
I think that's basically Vinay's
suggestion. Does that look reasonable?
That's a lot of database access to
get a unique primary key, just to be
able to return it from ejbCreate() -
especially in light of the fact, that
databases do it automatically, if
the table is created accordingly. Isn't
this kind of thing done
regularly?
I know this has nothing to do with jBoss. Thank
you. :-)
Ralph
----- Original Message -----
From: Jim
Downing <[EMAIL PROTECTED]>
To:
<[EMAIL PROTECTED]>
Sent: Friday, May 04, 2001 5:47
PM
Subject: Re: [JBoss-user] EJB question
> Check out
www.activescript.co.uk for a non-free ($99) component to
generate
>
unique ids. The author has also posted the pattern on
theserverside.com,
so
> you have something to work to if you want
to implement it yourself.
>
> jim
>
> ----- Original
Message -----
> From: "Ralph Jensen" <[EMAIL PROTECTED]>
>
To: <[EMAIL PROTECTED]>
> Sent: Friday, May 04,
2001 10:25 AM
> Subject: Re: [JBoss-user] EJB
question
>
>
> > The portability would be there in
terms of data access. How to tell the
> > database to autoincrement
when I create a table is probably always
> database
> >
specific. Or not?
> >
> > I'm not good at SQL. So how
would your suggestion look in code? What
would
> > the key
generator bean look like? Off which table would it work?
>
>
> > Ralph
> >
> > ----- Original Message
-----
> > From: Vinay Menon <[EMAIL PROTECTED]>
> >
To: JBOSS <[EMAIL PROTECTED]>
> > Sent:
Friday, May 04, 2001 4:29 PM
> > Subject: Re: [JBoss-user] EJB
question
> >
> >
> > Why don't you just use a
primary key generator bean to encapsulate the
key
> >
genaration? The ejbCreate can then work off that ejb and assign the
>
primary
> > key field to the primary key generated field? so your
autoincrement
> > essentially will not be on the same table as the
ejb but a different
one
> > and the primary key generator will
work off that table. [Also makes
sure
> > that you have complete
protability in terms of the database server!]
> >
> >
Vinay
> >
> >
> >
> > ----- Original
Message -----
> > From: Ralph Jensen
> > Sent: Friday, May
04, 2001 8:52 AM
> > To: [EMAIL PROTECTED]
>
> Subject: [JBoss-user] EJB question
> >
> >
>
> I asked this question elsewhere, but didn't get an answer. So:
>
>
> > An entity bean's ejbCreate(...) method MUST return the
primary key.
That
> is
> > not a problem, if I specify the
primary key myself and pass it to the
> > create(...)
method.
> >
> > But I want to let the database assign the
primary key by creating a
table
> > with an AUTOINCREMENT
default for the primary key column, like in this
> > example using
Cloudscape (part of SUN's J2EE v1.3):
> >
> > create table
myTable(
> > id INT DEFAULT AUTOINCREMENT
CONSTRAINT pk_id PRIMARY KEY,
> > someString
VARCHAR(6),
> > etc.
> > );
>
>
> > Then I can use INSERT like this:
>
> INSERT INTO mytable ( someString ) VALUES ( 'Hello'
);
> >
> > The database then assigns a unique value to the
id column of that new
> > record.
> >
> > If I do
this in the ejbCreate(...) method of my bean my problem is:
How
do
> > I know that value in order to return it? Is that
possible?
> >
> > Thanks
> >
> > Ralph
Jensen
> >
> >
> >
_______________________________________________
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>
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> > your FREE download of MSN Explorer
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> >
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>
>
> >
> >
> >
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