[seam-dev] How to store data in contexts

[Dan Allen]

On Fri, May 8, 2009 at 5:45 AM, <pmuir at redhat.com> wrote:

> Well you haven't produced a good use case for needing this abstraction
> (legacy interaction aside, ad that willbe privided through the seam2 layer).
> That would be a good start :-)
>

There is at least one important use case, though I think the solution is
going to be obvious when I say it. Ken Paulsen stated a best practice on the
JSF mailing list that I recommend as well, "that all EL should be given the
opportunity to be specified explicitly". Meaning you would use
#{requestScope.results} instead of just #{results}. In my research for the
article on JSF performance I found this to have a measurable impact on
performance. But clearly, that is something that should be provided by an EL
resolver. (Naturally, most scopes are already supported, so we just need to
add the ones that the JSF EL resolver doesn't know about, namely
conversationScope). So in the end, not a use case.

The second use case would be to pick off flags that libraries set into
scopes. So the values are already there, you just need to read them. Those
libraries aren't based on 299 (let's say) and they are sticking stuff into
these attribute maps that you need to read. On the flip side, you may need
to set attributes that those other libraries rely on. Let's say I am
integrating with a system developed a year or two ago (unfair to call it
legacy). I have to set some values in the session scope attribute map or
else it won't function...such as the current customer id, whether they have
accepted a disclaimer, the current user's login name, or whatever. That
library is going to go looking in the session map directly, so I can't just
make a producer.

The question becomes, how often does this second use case come up? I'll call
it read and write "flags" that libraries rely on. People that are dealing
with a lot of existing systems are going to have a lot of those cases. Those
that get to start anew won't have any. That's my use case, take it or leave
it.

-Dan

-- 
Dan Allen
Senior Software Engineer, Red Hat | Author of Seam in Action

http://mojavelinux.com
http://mojavelinux.com/seaminaction
http://in.relation.to/Bloggers/Dan

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