Re: Finally which ORM tool?

James Crosswell <james@xxxxxxxxxxxxxx> wrote:
Jon Skeet [C# MVP] wrote:
In pure ADO.NET you wouldn't have had an object tree which was meant
to represent the same state as the server, so the aliasing wouldn't
have been apparent.

Wouldn't you? What kind of things would you be passing back and forth
between your n-tier application server and client in an pure ADO.NET
implementation of the server? Did you pass datasets back and forth? I
sure didn't.

So if you *have* got an object tree, do you just not care about
aliasing at all? Often it's not a case of returning results to the
client - it's manipulation at the server end which may well being
sensitive to aliasing issues.

<snip>

I'm not sure if you're playing the devils advocate or if you're just
generally hostile to change but it seems to me that what I'm suggesting
is certainly an improvement over the existing frameworks which REQUIRE
me to write the above workaround because they REQUIRE sessions, even
though these are not required in order for these ORMs to do their work.

The decision to be session-based or not is pretty fundamental to an
ORM. If you don't want to use sessions, use an ORM which isn't session-
based, such as LLBLGen - but please don't try to suggest that no ORMs
should use sessions and manage aliasing and identity issues just
because they happen not to be issues for you.

That's the great thing about having a choice of frameworks. I have to
say that the fact that most ORM frameworks I've come across *do* have
identity management suggests that the requirement for it isn't as rare
as you seem to be making it out to be. If sessions have no benefit for
most people, why do you think the framework developers include them?

I've done plenty of n-tier work, and it's *not* the opposite for n-
tier frameworks. I suspect it depends on what you really want the ORM
system to do for you, but I've never regarded the session handling as
a problem, especially as Hibernate/nHibernate provide the ability to
"re-attach" an object from a previous session into a new one when you
want to.

I said sessions created a problem in n-tier (where they don't in desktop
apps) and if you've done a lot of n-tier work then you must realize this
is the case, since sessions in n-tier typically get created and
destroyed on a per thread basis and threads get created/destroyed on a
per request basis... requiring the workaround I described above in order
to effect updates.

You need to distinguish between the idea of a per-request session and a
"per user transaction" session. Again, Hibernate in Action deals with
this very well.

I wasn't aware of the re-attach behavior in nHibernate though... that
sounds interesting and would at least reduce the amount of needless code
I write to one line. I'll try to track down some info on this on the net
(although one of my projects is using XPO and they don't have such a
"feature"). Thanks for the tip.

I can't say I've looked at whether NHibernate itself has this, but I
should imagine it does given how it's present in Hibernate.

The Hibernate authors have put in a *lot* of thought when it comes to
this kind of thing, and they're certainly *not* just thinking of
desktop client/server apps.

--
Jon Skeet - <skeet@xxxxxxxxx>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too
.

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