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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