Maybe this has been discussed elsewhere, but looking at the EJB description I can see that
expressions are allowed basically anywhere.
This is an example how is should _not_ be done. I.e. the
"default-mdb-instance-pool" is certainly not something you would like to
configure by external means, do you?
Ike
On Oct 12, 2011, at 8:39 AM, Heiko Braun wrote:
The question you should ask yourself is which parts should be configured externally?
I.e. a typical scenario for expressions are configuration values that change depending on
the environment (staging/production).
I would suggest to be _very_ conservative about allowing expressions in your model.
It's definitely wrong to allow them anywhere, just because you are not sure if they
make sense.
As Brian said: We can add them anytime, but removing them is not an option.
Some further clarification what "adding expressions" actually means:
a) attribute meta data "expressions-allowed"
b) expressions values that we provide out of the box
a) is a requirement for b). But you are not forced to provide b).
My advice: Support expressions when it makes real sense. But back your decision with some
a use case.
Expressions are a powerful way to extend our default configuration means.
At the same time they lead to ambiguity and all kinds of error scenarios. So use them
sparely.
My 2 cents.
Ike
On Oct 11, 2011, at 6:26 PM, Brian Stansberry wrote:
> But otherwise, go ahead and support
> it. Expressions will be very important in cloud use cases where
> customizing the config file on a per-server basis is a poor option.
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