On 02/04/10 13:56 +0200, Mathias Behrle wrote:
> * Betr.: " [tryton-dev] Bring some attention on issue1422" (Fri, 2 Apr 2010
> 11:10:06 +0200):
>
> > There is a possible solution that will work only for PostgreSQL:
> >
> > CREATE UNIQUE INDEX "index" ON "table" ("name", COALESCE("parent", 0));
> >
> > Is there anybody who has better solution?
> >
> >
> > [1] http://bugs.tryton.org/roundup/issue1422
>
> Since it seems, that this issue has to be solved indivdually per DBMS and we
> don't want to provide our own logical layer, this is the way to go for me.
>
> http://dev.mysql.com/doc/refman/5.0/en/create-index.html
> http://bytes.com/topic/oracle/answers/65985-unique-constraint-null-values
I don't understand what you want to show in those links.
Any way, when looking at the comments in oracle thread, I thought about a
solution.
We could add a third integer field with the same value then "parent" but
without the foreign constraint. It will be filled by COALESCE("parent", -1).
The unique constraint will become:
UNIQUE("name", "parent_")
We could add a constraint to ensure that both values are always sync:
CHECK(COASLESCE("parent", -1) = "parent_")
The "parent_" field will be filled by the override of create and write
functions.
I know this sounds a little bit hacking but this is my best solution :-)
--
Cédric Krier
B2CK SPRL
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