Re: Caching of read-only DB contents in an EJB

[Lahooti, Hamid]

>I'm quite confused by this thread.  I was under the impression that one
>of the reasons that *entity* beans exist at all in the specification is
>to effectively serve as data caches for the underlying data store.  That
>is, there is a person record on disk somewhere, but you deal with the
>Person entity bean instead, because it will usually be (activated) in
>memory.
A cache needs to be kept in sync with its data source.
For that you need update notifications generated by
data source. To be a subscriber to events, you need
singletons which are not supported in ejb spec.

So, to maintain entity data in sync with the database,
there is only one way: refresh entity attributes from
the database every time a new transaction starts. the
container achieves this by calling ejbLoad and ejbStore
within the boundaries of a transaction. This implies
that entity data is not cached in the real sense.


Hamid

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