Re: EditingContext Newbiee Question
Re: EditingContext Newbiee Question
- Subject: Re: EditingContext Newbiee Question
- From: David LeBer <email@hidden>
- Date: Fri, 1 Aug 2008 23:22:51 -0400
On 1-Aug-08, at 8:33 PM, Gustavo Pizano wrote:
Hello everyone, I just wanted to ask a noob question. Everywhere I
look I see about the EditingConext, as I know, it function its to
hold instances of the EO's so they can interact each other and so.
in the tutorials and the documentations, they talk most of the part
about the defaultEditingContext, from the session, or the
apllication, so my question is, when its necessary to use the
defaultEditingContext, and to create a new one?.
This thing about the EditingContext its spining my head a little.
Tutorials generally don't use anything other than the
defaultEditingContext because it adds a layer of complexity that the
authors (I assume) feel will detract from the core purpose of the
tutorial.
However, this tends to give beginners a false impression of how most
real-world applications are written and also fails to demonstrate the
pitfalls of a single EC design.
Lets take a (completely contrived) example:
Your application is using the defaultEditingContext. Your user enters
a form that creates a new EO. Half way through they decide to abort
and hit the back button a couple of times and go somewhere else in the
site.
The defaultEditingContext is now dirtied with that new EO. If the user
later performs any action that calls saveChanges on the defaultEC it
will try and commit the EO, it might fail giving your user a
completely unexplainable validation error, or it might succeed saving
unwanted and probably invalid data.
So my general rule of thumb is to never use the defaultEditingContext
for any edit actions. I always create new ECs for any task that is
going to require editing.
Using Project Wonder's ERXEC makes this particularly painless as it
handles the necessary EC locking automagically.
Other options are documented here: <http://wiki.objectstyle.org/confluence/display/WO/EOF-Using+EOF-Context+and+Database+Locking
>
;david
--
David LeBer
Codeferous Software
'co-def-er-ous' adj. Literally 'code-bearing'
site: http://codeferous.com
blog: http://davidleber.net
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--
Toronto Area Cocoa / WebObjects developers group:
http://tacow.org
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