[nhibernate-issues] [JIRA] Commented: (NH-814) Resetting of properties after initial set violates constraints we want to protect

[NHibernate J. <mik...@us...>]

    [ http://jira.nhibernate.org/browse/NH-814?page=3Dcom.atlassian.jira.pl=
ugin.system.issuetabpanels:comment-tabpanel#action_15722 ]=20

Nels P. Olsen commented on NH-814:
----------------------------------

Having your property setters ignore requests to reassign the same value sho=
uld be sufficient.  Beyond that it is merely a potential optimization to NH=
ibernate to keep it from repeatedly setting the a property to the same valu=
e.  All of our entity property setters ignore requetsts to reassign the sam=
e value, both so that some properties can enforce the "set once" rule, and =
also so that PropertyChanged events (all our entities implement INotifyProp=
ertyChanged) don't get fired and time isn't otherwise wasted validating the=
 value.

> Resetting of properties after initial set violates constraints we want to=
 protect
> -------------------------------------------------------------------------=
--------
>
>                 Key: NH-814
>                 URL: http://jira.nhibernate.org/browse/NH-814
>             Project: NHibernate
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 1.0.2
>            Reporter: Jim Showalter
>            Priority: Major
>             Fix For: LATER
>
>
> We have properties on objects that are supposed to be set only once, when=
 first reading an object back from the database. Once in memory, they are n=
ot supposed to be set again, and attempting to do so is supposed to throw a=
n exception. Unfortunately, nhibernate's behavior appears to be less predic=
table than we had thought. It assigns properties more than once. For exampl=
e, when merging a disconnected object, it loads one from the database (thus=
 setting the properties), and then sets them again from the other object, t=
hus violating the set-once rule. There are other cases similar to this. We =
modified our rule to allow setting to null (or some other value indicating =
not-yet-set) as many times as desired, then setting to some actual value, a=
nd allowing setting to that same value as many times as desired. Setting to=
 a different value once set throws an exception. This seems to pacify nhibe=
rnate, but we're not certain that it will work in all cases, and the behavi=
or of nhibernate as far as resetting properties is concerned is undefined. =
Our request is for nhibernate to be enhanced to have a notion of set-once, =
which would be stated in the HBM file. This would make a property immutable=
, with the sole setting of that property to be done on reading in from the =
database. On save, a set-once property would be assumed to have already bee=
n set--nhibernate would not set it itself when saving, only when reading.
> This same request has been filed for hibernate as HHH-2245.

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