Hello Navaneeth,
Suppose you have your EJBs in a JAR file and suppose you have designed it to
use databases like, for example Oracle. Suppose now you're using a class to
query to database for the next primary key.
Now we have a JAR file with the EJBs and this class.
At this moment, suppose I want to deploy your components in my system. And
suppose I have MySQL. There is no problem, ok.
But suppose I have not a database like Oracle, for example a database which
generates the primary with another method... and the class we use to do this
is not valid.
A solution could be change this class with another implementation but with
the same name (un-jar the file, obtain the new class, re-jar, and everything
to have two different classes with the same name! ... argh!). Think that all
those things must be done by me: a deployer, not the developer. Think that I
don't know anything about your source code.
But if you had used a session bean to query for the next primary key, you
only have to give me the new component (another session bean with other
classes -other names, other implementations-) specially developed to access
to my database. At deployer time, I only have to put (and to bind) the
suitable component to obtain the next key from database.
It's only an idea. I want you to comment it; it will be appreciated.
Thank you. Regards
Luis Canals.
-----Original Message-----
From: Navaneeth [mailto:[EMAIL PROTECTED]]
Sent: martes, 12 de septiembre de 2000 14:26
To: [EMAIL PROTECTED]
Subject: Re: Generating ID???
Hi Luis ,
Just a simple question ...
Why not use a simple java class to do this for you ??
Why did u go for a session ejb ??
Regards,
Navaneeth
----- Original Message -----
From: Luis Canals <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Friday, September 08, 2000 9:12 PM
Subject: Re: Generating ID???
> Hi,
>
> well, I implment this method in a Session Bean in order to be able
> to change this Session Bean to access to another "exotic" database without
> recompiling or redeploying your Entity Beans. Again, an example: you can
> have two types of this Session Bean called DataBaseSpecificOracle and
> DataBaseSpecificSQLServer, with methods specifics for each database; at
> deploying time, you only have to link the reference in your JNDI to the
> desired Session Bean, depending on the database.
>
> In the other hand, you say "supposedly written by experts"
.."experts"....
> I think there are more experts in discussion lists like that. If your
> question has not been made by "these experts" (and answered), I think you
> know more about EJBs than them... it's logical, isn't it? If you don't
know
> anything, you can't ask anything; if you know a lot, you have a lot of
> questions too.
>
> Bye.
> Luis Canals.
>
> -----Original Message-----
> From: Jerson Chua [mailto:[EMAIL PROTECTED]]
> Sent: viernes, 08 de septiembre de 2000 17:09
> To: [EMAIL PROTECTED]
> Subject: Re: Generating ID???
>
>
> Hello Luis...
> That's what we're currently using but instead of implementing it in a
> session bean, we
> implemented the query in a private method of the particular entity bean
> using it.
> I'm asking this question cause I thought that there's something wrong with
> the
> implementation. I thought I'm missing something cause articles like the
one
> I read are
> supposedly written by experts.
>
> Jerson
>
> --- Luis Canals <[EMAIL PROTECTED]> wrote:
> > Hello,
> >
> > I think your right: it doesn't works because two (or more) beans
> can
> > take the same id. My solution is a query (to the database) to obtain the
> > next value for the primary key. For example, in Oracle, something like
> > SEQ_XXX.NEXTVAL. To do this, I propose the use of Stateless Session Bean
> > (specific to each Database) which will take the next value with a query
to
> > database. If you change your database, your only must change this
> Stateless
> > Session Bean.
> >
> > For example, you have something like that:
> > public class DataBaseSpecificLikeOracleBean implements SessionBean {
> > public int nextPrimaryKey(String table) {
> > String query1 =
> > ctx.lookup("java:comp/env/SQLNextValFirstPart"); // For example
> > SELECT SEQ_
> > String query2 =
> > ctx.lookup("java:comp/env/SQLNextValSecondPart"); // For example FROM
DUAL
> >
> > query = query1 + table + query2;
> > // Execute the query and return the result
> > }
> > }
> >
> > In your Entity Bean:
> >
> > public class CustomerEntityBean implements EntityBean {
> > // Instead of getEJBHome().findNewest() use..
> > DataBaseSpecific dbs =
ctx.lookup("EJBDataBaseSpecific");
> > nextKey = dbs.nextPrimaryKey(0
> > protected long getNextKey() {
> > long nextKey = 0;
> >
> > Customer newestCustomer = ((CustomerHome)
> > entityContext.getEJBHome()).findNewest();
> > // the implementation of findNewest is not shown,
> > // i guess the findNewest returns the bean with the
> highest
> > id/primary key
> > // in my point of view this is like select max(id) from
> > customer + 1
> > nextKey =
> ((CustomerKey)newestCustomer.getPrimaryKey()).key
> > + 1;
> > return nextKey;
> > }
> > }
> >
> >
> > And you need, in your JNDI the two parts of a query to obtain next
value.
> > You can use another DataBaseSpecificBean (for other databses) with the
> same
> > interface and put it instead of this implementation.
> > This is not a final solution, only an idea... please, think about it and
> > rebuild it!
> >
> > Regards.
> >
> > Luis Canals.
> >
> >
> > -----Original Message-----
> > From: Jerson Chua [mailto:[EMAIL PROTECTED]]
> > Sent: viernes, 08 de septiembre de 2000 9:39
> > To: [EMAIL PROTECTED]
> > Subject: Generating ID???
> >
> >
> > Hello Guys...
> >
> > I've read an IBM article and it has an example in generating id/primary
> key.
> > I have a
> > doubt that 1 or more bean can get the same id. I want to verify this
> doubt.
> > Is this
> > scenario possible?
> >
> > 1. Customerbean1 retrieves max id
> > 2. Customerbean2 retrieves max id
> > 3. Customerbean1 increments maxid and store to db
> > 4. Customerbean2 increments maxid and store to db
> >
> > public class CustomerEntityBean {
> > public void ejbCreate(String name, int type) {
> > key = getNextKey();
> > ...
> > }
> >
> > protected long getNextKey() {
> > long nextKey = 0;
> >
> > Customer newestCustomer = ((CustomerHome)
> > entityContext.getEJBHome()).findNewest();
> > // the implementation of findNewest is not shown,
> > // i guess the findNewest returns the bean with the
> highest
> > id/primary key
> > // in my point of view this is like select max(id) from
> > customer + 1
> > nextKey =
> ((CustomerKey)newestCustomer.getPrimaryKey()).key
> > + 1;
> > return nextKey;
> > }
> > }
> >
> > What's your opinion? Will this design work?
> >
> > Jerson
> >
> >
> > __________________________________________________
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> >
> >
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