kdlitwak wrote:
>
> Why can't an entity bean do its own transaction demarcation? I could
> understand this for an entity bean that is totally under the control of
> the container but what if I've written my own ejbLoad and ejbStore code
> because my entity represents, say, an object database entity. Why can't
> I do my own begin, commit, rollback, etc.?
Because then the EJB server will not be able to control it.
Transactions are required to enforce transactional integrity across the
usage of an entity bean and that usage spans beyond load/store,
including changes the occur between load/store, access to multiple beans
in the same transaction, etc.
Given a good squeeze EJB transactions can be mapped into ODMG
transactions, though the mapping is not trivial.
> In this connection, sort of, just how complex can CMP be? I gather
A bit more than BMP :-)
> from what I've read in the spec that joins are possible, as specified in
> the DD. How many ways? What about more complex stuff? OODBMSs and
> non-database sources must use BMP right? Thanks.
Support for joins depends on the CMP implementation you are using. EJB
actually doesn't define how they are handled and an EJB server can be
complaint and not support joins. There's also no specification of what
happens in one-many and many-many relations when the relation maps to a
second entity bean.
OODBMS can also be used as CMP, but you either have to squeeze them in,
or use an XAResource support instead of the ODMG Transaction API.
Other non-database sources can also be used with CMP, provided you can
find such a CMP implementation.
arkin
>
> Ken
>
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