Обсуждение: NULL becomes default

A surrogate key has been introduced on a table with modifiers:
  Column    |            Type             | 
Modifiers
-------------+-----------------------------+------------------------------------------------------------new_id    |
integer                    | not null default 
 
nextval(('some_id_seq'::text)::regclass)

However, some legacy software inserts into the table by first getting column 
names and then composing an INSERT for all the columns, filling in any 
undefined values with NULLs.

Thus when it attempts to insert a row I get a:

ERROR:  null value in column "new_id" violates not-null constraint

Thus I would like NULLs in such INSERTs to be treated as DEFAULT rather than 
violating the constraint.  Is there an easy way to do that at the database 
level?

Thanks

Julian

Hi, Julian,

Julian Scarfe wrote:
> A surrogate key has been introduced on a table with modifiers:
> 
>   Column    |            Type             | Modifiers
> -------------+-----------------------------+------------------------------------------------------------
> 
> new_id    | integer                     | not null default
> nextval(('some_id_seq'::text)::regclass)
> 
> However, some legacy software inserts into the table by first getting
> column names and then composing an INSERT for all the columns, filling
> in any undefined values with NULLs.
> 
> Thus when it attempts to insert a row I get a:
> 
> ERROR:  null value in column "new_id" violates not-null constraint
> 
> Thus I would like NULLs in such INSERTs to be treated as DEFAULT rather
> than violating the constraint.  Is there an easy way to do that at the
> database level?

Did you try a "before insert" trigger that checks new_id for null
values, and replaces it with nextval()?

Markus


-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

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>> Thus I would like NULLs in such INSERTs to be treated as DEFAULT rather
>> than violating the constraint.  Is there an easy way to do that at the
>> database level?

From: "Markus Schaber" <schabi@logix-tt.com>

> Did you try a "before insert" trigger that checks new_id for null
> values, and replaces it with nextval()?

So thinking about this a little more, it requires me to be able to change a 
column value to DEFAULT (unless I implement the default from scratch in the 
trigger, but that feels messy).  I don't have much experience of triggers: 
can I do that?

Thanks

Julian 

On Sun, Aug 20, 2006 at 11:34:48AM +0100, Julian Scarfe wrote:
> So thinking about this a little more, it requires me to be able to change a 
> column value to DEFAULT (unless I implement the default from scratch in the 
> trigger, but that feels messy).  I don't have much experience of triggers: 
> can I do that?

DEFAULT won't work for this case, I don't think; you want to set it
to the nextval() of the sequence or whatever it was you were trying
to do.  But it's not messy: this is precisely the sort of thing
BEFORE triggers are good at.

A

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