Dane Jones wrote:
>
> Thanks Dion for your quick response.
>
> However your answer is actually the very cause of my confusion.
>
> As far as I can tell, the ejbFind*() methods are called after the
> ejbCreate() is invoked. Is that correct? In that case, if cust
> already exists (I don't mean _cust_ per se, but the table row that will be
> used to fill the EJB's attributes) what's the point of an
> INSERT statement within ejbCreate() when it's already there and the
> ejbFind*() method can retrieve the existing record?
>
> Does the ejbCreate() method *have* to contain an INSERT statement (for BMP)?
> And does the ejbRemove() method have
> to contain a DELETE statement?
>
> I know I'm missing something quite logical, and this is making me feel quite
> stupid.
Dane,
Perhaps the point you are missing is that the Bean Instance is considered to
exist whenever there is a database record that corresponds to the PK of the
bean. It is even considerd to exist while the EJB server is down or the database
is offline. Since the purpose of ejbCreate() is to create Bean Instances, when
the database is populated by a non-EJB application ejbCreate is never called.
Bean Instances should not be confused with the three other types of "instance".
First, the "Object Instance" is an instance of the Java class that has the
bean's methods on it. Object Instances are created and destroyed by the server.
A simplistic server would create an Object Instance when a Bean Instance was
loaded into memory and would destroy the Object Instance at the end of the
transaction that created the Object Instance. In practice, the server creates
pools of such instances and allocates them to Bean Instances as necessary.
Second, the "Proxy Instance" which is an object that exists in the client and is
operated upon by the client and lasts as long as the client needs it.
Finally there is the " EJBOBject Instance" which is what the Proxy Instance is a
proxy to. I mention it only because it is discussed in the EJB spec - it is
quite irrelevant to the EJB developer. Servers may create these (or they may
not). If used by the server they probably exist while the "Proxy Instance"
exists.
To summarise:
- Bean Instances last as long as the application needs the data
- Object Instances last as long as the server needs them
- Proxy Instances last as long as the client needs them
- EJBObject Instances may or may not exist at all
Hope this helps...
cheers... Ian
Ian McCallion
Alexis Systems Limited
Romsey, UK
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