Views and default values

On Fri, Apr 06, 2001 at 12:24:09PM +0100, Michael Ansley wrote:

Data Base:

create table foo (
cod serial primary key,
explication text,
silly bool default 't');

create view v_foo as
select * from foo;

create rule v_foo_ins as on insert to v_foo do instead
insert into foo values (
NEW.cod,
NEW.explication,
NEW.silly);

You should probably have this:

create rule v_foo_ins as on insert to v_foo do instead
insert into foo (explication, silly) values (
NEW.explication,
NEW.silly);

The rule is trying to insert NEW.cod, which is null, into the table. This
rule let's the cod field take care of itself.

That is valid for 'cod' but not for 'silly'. I'd like that if insert value
is null, then I get default value, but if insert value is not null, this is
value that is saved.

Any idea?...

Thanks.

David

I think that a coalesce might work here, something like:

create rule v_foo_ins as on insert to v_foo do instead
insert into foo (explication, silly) values (
NEW.explication,
COALESCE(NEW.silly, 'DEFAULT_VALUE'));

Obviously you replace the DEFAULT_VALUE with whatever you want your default
to be.

Cheers...

MikeA

-----Original Message-----
From: DaVinci [mailto:bombadil@wanadoo.es]
Sent: 06 April 2001 12:27
To: pgsql-general@postgresql.org
Subject: Re: [GENERAL] Views and default values

On Fri, Apr 06, 2001 at 12:24:09PM +0100, Michael Ansley wrote:

Data Base:

create table foo (
cod serial primary key,
explication text,
silly bool default 't');

create view v_foo as
select * from foo;

create rule v_foo_ins as on insert to v_foo do instead
insert into foo values (
NEW.cod,
NEW.explication,
NEW.silly);

You should probably have this:

create rule v_foo_ins as on insert to v_foo do instead
insert into foo (explication, silly) values (
NEW.explication,
NEW.silly);

The rule is trying to insert NEW.cod, which is null, into

the table. This

rule let's the cod field take care of itself.

That is valid for 'cod' but not for 'silly'. I'd like that
if insert value
is null, then I get default value, but if insert value is
not null, this is
value that is saved.

Any idea?...

Thanks.

David

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Michael Ansley <Michael.Ansley@intec-telecom-systems.com> writes:

I think that a coalesce might work here, something like:

create rule v_foo_ins as on insert to v_foo do instead
insert into foo (explication, silly) values (
NEW.explication,
COALESCE(NEW.silly, 'DEFAULT_VALUE'));

Obviously you replace the DEFAULT_VALUE with whatever you want your default
to be.

This isn't really a good solution, because it prevents explicit
insertion of a NULL (which isn't something that DaVinci cares about
in the particular example, but it would be annoying in related cases).
Also, you might not want your rule to have to know just what default
value the table has.

There is a better answer: INSERT's default-value-addition machinery
operates upstream of the rule rewriter, so it could work for a view.
Unfortunately the system won't accept
ALTER TABLE v_foo ALTER COLUMN silly SET DEFAULT 't'
but I see no real good reason why it shouldn't. DaVinci could either
remove the restriction against doing this (quick code hack) or insert
the appropriate pg_attrdef entry by hand (ugly...).

Meanwhile, if Bruce is paying attention, please add a TODO list item
to allow column defaults to be set on views. (Please note pg_dump
would need to be fixed to know it needs to dump these, too.)

regards, tom lane

On Fri, Apr 06, 2001 at 01:26:39PM +0200, DaVinci wrote:

On Fri, Apr 06, 2001 at 12:24:09PM +0100, Michael Ansley wrote:

Data Base:

create table foo (
cod serial primary key,
explication text,
silly bool default 't');

create view v_foo as
select * from foo;

create rule v_foo_ins as on insert to v_foo do instead
insert into foo values (
NEW.cod,
NEW.explication,
NEW.silly);

You should probably have this:

create rule v_foo_ins as on insert to v_foo do instead
insert into foo (explication, silly) values (
NEW.explication,
NEW.silly);

The rule is trying to insert NEW.cod, which is null, into the table. This
rule let's the cod field take care of itself.

That is valid for 'cod' but not for 'silly'. I'd like that if insert value
is null, then I get default value, but if insert value is not null, this is
value that is saved.

what would be NICE would be something that did

select FIELD_DEFAULT(thistable.myfield);

't'::bool

select FIELD_DEFAULT(afield) from sometable;

'now'::timestamp

create view mynewview as select * from mytable;
create rule myrule as on insert to mynewview

do instead
insert into mytable values (
coalesce(new.field1,FIELD_DEFAULT(mytable.field1)),
coalesce(new.field2,FIELD_DEFAULT(mytable.field2)),
coalesce(new.field3,FIELD_DEFAULT(mytable.field3)),
coalesce(new.field4,FIELD_DEFAULT(mytable.field4))
);

which would answer a question in a separate thread -- how to get
the default value of a column from a table's definition...

would it be difficult to create such a function?

--
americans should never read anything so subversive as what's at
http://www.salon.com/people/col/pagl/2001/03/21/spring/index1.html

will@serensoft.com
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