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Begin forwarded message:

From: Cail Borrell <email@hidden>
Date: 20. aug 2008 18.50.44 GMT+02:00
To: Ondřej Čada <email@hidden>
Cc: Cail Borrell <email@hidden>
Subject: Re: sequential numbering across more instances

Hi Ondra,

I believe I did leave out a few details :-)

That would be kind of problem, for I am working with a legacy database which already contains lots of rows.

You don't have to change the database. When I say "internal data type" I mean in the
context of the EOModel.

Your attribute could look some thing like this

   columnName = <unique column>;
   externalType = NUMERIC; <- an integer column would be fine to
   name = <attribute name>;
   valueClassName = NSString;
   width = 256;

In your EO class you can have the accessors

public void set<attribute name>(Object value)
public Object <attribute name>()

the you can set the sql value however way you desire since
the set method uses takeStoredValueForKey to store the value.

(select max(<unique column>) from (<table name>))+1

could I not? (Assumed there is at least one non-nil column, which it happens to be there all right -- otherwise I could use the improvements Florijan or Francis suggested.)

The coalesce is just used in case you are starting with an empty table
and need some initial value.

-Cail

On 20/08/2008, at 16.54, Ondřej Čada wrote:

Cail,

On Aug 20, 2008, at 3:47 PM, Cail Borrell wrote:

If you change the internal data type of your unique attribute to String

That would be kind of problem, for I am working with a legacy database which already contains lots of rows.

Not that it would be entirely out of question, but it would complicate things considerably :(

you should be able to use a little sql injection when inserting your record.

Sorry, I got lost here. You mean I should catch the generated SQL in EOF just before sent to the database, and replace the value which is sent to the column by the "coalesce(...)+1" _expression_?

Just set the value of your unique column to something like:
coalesce (select max(<unique column>) from <table name>, cast (1000000 as <unique column data type>)) + 1
and invalidate the eo after insertion.

If not, colour me please dumb and elucidate.

If so... well, I haven't considered this possibility -- good point!

Perhaps I could do the same with an integer column and simpler _expression_

(select max(<unique column>) from (<table name>))+1

could I not? (Assumed there is at least one non-nil column, which it happens to be there all right -- otherwise I could use the improvements Florijan or Francis suggested.)

In the latest versions of FrontBase triggers are enabled by default.

Good, didn't know that. Thanks!
---
Ondra Čada
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