Re: EOF and the Observer Pattern
Re: EOF and the Observer Pattern
- Subject: Re: EOF and the Observer Pattern
- From: Chuck Hill <email@hidden>
- Date: Thu, 30 Oct 2008 13:46:53 -0700
Hi David,
On Oct 30, 2008, at 2:44 AM, David Avendasora wrote:
I have several places in my application where a large number of EOs
exist in the DB that are directly dependent upon other EOs. If the
depended-upon EOs change, then all the dependent EOs may need to be
updated.
Are these all guaranteed to be in memory at the same time? Do you run
multiple application instances?
This seems to me like the perfect use of the Observer Pattern.
Or not. It sounds more like Publish - Subscribe. Or is that the
same...?
For example. If a Part's BOM is updated the nutrition information
for that Part may need to be updated as well. Calculating the
current nutrition information is too expensive to do it everywhere
it is needed so it is saved in the database. I also maintain
historical nutritional information as well and that shouldn't be
updated, only the current information should be.
What I'd like to do is to have the "current" Nutrition object
observe the Part object.
Or have the part broadcast a NSNotification when it is modified. Then
any other objects can choose to subscribe to this notification if they
deem it interesting.
If the Part object is updated in a significant way, then the
Nutrition object will get notified to update itself.
Publish - Subscribe gives a bit more decoupling between the change and
the response.
What I'm trying to figure out is how to persist this information. I
don't think I want to model the relationship, do I?
I don't know. It is your model. What is it you are thinking of
persisting?
I looked at EOObserving but I think that's more about catching
changes between two objects already in memory.
How would I model EOEnterpriseObject <<->> EOEnterpriseObject
anyway? Using EOIDs?
Now, I think I am lost.
Chuck and muddying the waters again.
--
Chuck Hill Senior Consultant / VP Development
Practical WebObjects - for developers who want to increase their
overall knowledge of WebObjects or who are trying to solve specific
problems.
http://www.global-village.net/products/practical_webobjects
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