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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