Re: Setting an attribute based on PK?

If all you need is an unique value, then why torture EOF?  Some possibilities:
- create a session and grab the session ID.  Quick, dirty, effective.
- use one of the digest algorithms to digest information on the object and
produce a unique value
- use EO_PK_TABLE or the database's PK generation support to generate a
number just for this purpose.
- use and EO to keep track of the last used value, use this value +1 and
update it on an insert of the other object


More below.

At 04:16 PM 25/04/2004 +0800, Ashley Aitken wrote:
>
>Howdy All,
>
>I want to set an attribute (not the primary key) based on the 
>primaryKey value.
>
No.  You want to set an attribute (not the primary key) to a unique value.
You've just fixated on the primary key value.  :-)

>But, of course, the primary key is not generated 
>until during the initial saveChanges.
>
Actually not until quite late in the game.


>Here's what I tried to do:
>
>Briefly, I added a custom primary key generation delegate that calls 
>the standard primary key generation method but then also calls a method 
>to set the other attribute.
>
>All this seems to work fine - well all the code gets called - I see the 
>primary key being generated on save, I see the original value of the 
>other attribute as expected, I see the updated value as expected.
>
Yeah....

>The only thing is, it still saves the original value of the other 
>attribute.  I seem to remember it is ill-advised to change an EO during 
>validation (although this is not validation, probably later) maybe this 
>is similar.
>
You're changing things that EOF considers already settled.  This is way,
way too late to be mucking about changing attibute values.


Chuck


>My thinking is that the operations would happen in this order:
>saveChanges
>     validation (I have none)
>     primaryKey generation + changing other attribute (using 
>takeStoredValueForKey)
>     generating and executing SQL to save new row
>
>But, as I mentioned, I can't seem to make my changes to the other 
>attribute get used in the actual save (the changes occur - I can see 
>them with storedValueForKey - but are not written to the database).
>
>Any ideas?  If not what is wrong with this, how better to do what I am 
>trying to do.
>
>Thanks in advance,
>Ashley.
>
>PS Why do I want to do this?
>
>The entity has an entityCode (not the primary key) but used by the user 
>to refer to items (so it should be unique, but not strictly so).  I 
>give the user an opportunity to set this entityCode (in fact, I require 
>it) but if they set it to "*" then it should be auto-generated.  To do 
>that, I am, at present, just trying to give it the value of the primary 
>key (an integer to string), but later I may want to combine it will 
>some other attributes to make a more meaningful entityCode (eg WOT-12).
>
>
>--
>Ashley Aitken
>Perth, Western Australia
>mrhatken at mac dot com
>
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--

Chuck Hill                                 [email protected]
Global Village Consulting Inc.             http://www.global-village.net