The answer to this question is that of course they are not NECESSARY, but they
are handy for rapid reliable application development and worthy of serious
consideration for any EJB application.
The problem with Entity Beans is that application servers vary widely in the
degree of effort put into entity bean implementation, so developers are nervous
of using Entity Beans in case their chosen pattern of usage is inappropriate for
their chosen server.
I suspect (based on personal experience plus monitoring of this list) that there
is a limited set of usage patterns that represent most EJB applications. Here is
my list:
1. A large set of read-only entities
2. A singleton read-only entity of up to (say)
100k bytes of data that answers questions about
the data
3. CRUD (Create Read Update Delete) on a large body
of data (large is defined so that data is unlikely
to be in the cache when next needed - eg 100000
entities randomly accessed).
(a) Single coarse-grained update.
(b) Multiple fine-grained updates in a single transaction.
4. CRUD on a small body of data (small is defined so
that efficient caching would be of significant
benefit, eg 100 entities randomly accessed)
(a) Single coarse-grained update.
(b) Multiple fine-grained updates in a single transaction.
5. Fuzzy search, where user is seeking to work with
a single instance, but search parameters are
entered that may result in a long list of matches
(eg search on a common lastname to find a
particular customer record). Solution should asssume
use of findByLastName rather than SQL from a session
Bean.
It would be useful if each app server vendor could characterise their server's
behaviour with respect to each of these seven patterns allowing a potential user
of the pattern to estimate how many database calls would be made, how much data
would be cached, and how to configure the server to reach the desired
performance.
Is this expecting too much?
========================================
Ian McCallion
Alexis Systems Limited
Romsey, UK
Tel: +44 1794 514883
Fax: +44 1794 501692
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