OK, I misunderstood the problem you're talking about. So, yes, the
state-saving method is immaterial. The state-saving method can be
material if a user has more than one window open within a session, in my
experience.
Well, it's definitely true that DataModel is a "local" snapshot of what
one queried at a point in time. Yes, it can become stale.
Typically, your table would contain a list of keys, and, once the user
has clicked on one of the entries, you would ask the DataModel for the
appropriate rowIndex that was selected, and then, at that rowIndex, you
would get the key for that row, go to the database for the detail, and
then return "success", at which point the detail for that key is
displayed, or the detail and the summary are both displayed, or
whatever.
If you want to redisplay a refreshed version of the summary as well as
the detail, you'd query the database for that as well.
I guess I'd have to have more information to see where the stumbling
block is. Maybe I'm not having any issues with it because I'm using
<t:saveState>.
- Brendan
-----Original Message-----
From: Kevin Galligan [mailto:[EMAIL PROTECTED]
Sent: Monday, August 29, 2005 3:23 PM
To: MyFaces Discussion
Subject: Re: Concerning DataModel usage plus overhead?
Hmm. I could, but I'd bet it would be no different. I don't think that
takes care of the fundamental problem, which is as follows...
*** Get list of entries ***
Date Name Id Index
8/22/05 First Entry 1 0
8/22/05 Second Entry 2 1
8/24/05 Third Entry 3 2
8/25/05 Fourth Entry 4 3
That's what you see on your page (the "Index" column would really be
links to a detail page, not an index number. However, to the system,
its an index number). While you're looking at that, somebody else adds
the following...
Date Name Id
8/20/05 Older Entry 5
Lets say you then click on entry number 2, "Second Entry", in your list.
To the system you clicked on index number '1'. It will get the list
of entries, and the entry at index '1' will be selected.
Since an entry was added while you were looking at the page, when you
get to the detail page you'll actually see "First Entry".
I don't think saving state on the client has anything to do with this.
Its still select-by-index instead of by id.
This is the first issue I had with the DataModel pattern. You can avoid
this by keeping the entries in the session. However, every time you go
to the list page you'll see stale data. You'd need to code an explicit
function and link to dump and refresh the data (and make sure your users
are aware that they are looking at stale data).
The extended dataTable takes care of this with *forceIdIndexFormula*,
but then you still have the issue that every time you click on a link,
the system does a full data grab. Worse yet, it then has to scan
through each to find the particular id (*** I may be wrong about that.
If I am, somebody please tell me. This is part of the reason why I'm
posting ***).
CONNER, BRENDAN (SBCSI) wrote:
Out of curiosity, are you setting javax.faces.STATE_SAVING_METHOD to
client in your web.xml? If not, can you try doing that and seeing if
you observe the same behavior?
- Brendan
-----Original Message-----
From: Kevin Galligan [mailto:[EMAIL PROTECTED]
Sent: Monday, August 29, 2005 2:50 PM
To: [email protected]
Subject: Re: Concerning DataModel usage plus overhead?
I tried to send this, and I think it failed. Anyway...
Rick, "To me the above is just really goofy. Unless, there are
security
constraints to me it makes sense to get the item you want back based
on
some key."
You and I are on the same page. I'm not sure I'd so far as goofy, but
I
think for particular domains, the DataModel pattern isn't really the
way
to go.
Brendan "It's just that JSF offers the DataModel abstraction such
that,
when the user clicks on your link, your program just has to ask
DataModel for rowIndex to locate the row that was selected. *It's
designed to simplify your coding.*"
If you look through the post I pasted in my message, I had a fairly
serious problem with the DataModel. I was using it to show a list of
entries from a database. When the user visits the page, it grabs the
list from the database and displays it. I was able to take the
example
from the O'Reilly book and break it. How? Basically...
1) Get the list of entries on one browser screen
2) Open a different browser and add an entry
3) Go back to the original browser and click an entry
If you do it in the "magic" order, you'll wind up selecting a
different
row than you clicked on. This is because the DataModel uses a
numerical
index instead of a internally meaningful id value.
If you use the extended dataTable and the forceIdIndexFormula, you can
index by an id value, but its still doing some strange dynamics. I'm
guessing, but I think when the user clicks, the system would have to
get
the full list again, scan through it, and then select the value you
want. Its self-consistant in that it'll select the correct entry, and
maybe its conceptually simpler, but at the expense of significant
processing and data access.
In the post I asked if anybody used more of a hybrid approach. Do
your
lists with "classic" link-by-id design, grab the singular value, and
pass to a jsf page. I also had some thoughts on implementing this
directly in JSF, but in a way that avoided double data grabs or
link-by-index designs.
Ok, back to my reguarl day job...
(thanks in advance, again)
CONNER, BRENDAN (SBCSI) wrote:
Yes, you could do your own parameter passing. It's just that JSF
offers
the DataModel abstraction such that, when the user clicks on your
link,
your program just has to ask DataModel for rowIndex to locate the row
that was selected. It's designed to simplify your coding.
In the applications I've worked on, we very rarely have to explicitly
pass request parameters. Pretty much everything is in the bean.
- Brendan
-----Original Message-----
*From:* Rick Reumann [mailto:[EMAIL PROTECTED]
*Sent:* Monday, August 29, 2005 2:09 PM
*To:* MyFaces Discussion
*Subject:* Re: Concerning DataModel usage plus overhead?
On 8/29/05, *Kevin Galligan* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
If you use the standard dataTable, you have to
keep your values in session between the time you show the list
and when
they click on the value. If you get the values from the db
each
time,
you open the possibility that the index will have changed, and
the
selected value will be incorrect. If you keep the values in
session,
its keeping a lot of data around, and you need to explicitly
code a refresh.
To me the above is just really goofy. Unless, there are security
constraints to me it makes sense to get the item you want back
based
on some key. Maybe for example you are looking at a list of care
models on a page, then you want to see the details of the car. It
makes most sense to me to click on the car model passing the id of
the model you want, you look up the model and you pass it back.
When
you need the list of cars back, get a fresh set from the backend.
If
you need caching, cache at the persistence layer.
I don't see the advantage of saving the state of a DataModel, but
I'm new to all of this, so maybe I'll see the light at some point.
--
Rick
