Обсуждение: Views and default values
Hello.
I have a problem (one more ;) with views, rules for inserting and default
values.
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);
What is my problem with this?... It is easy to make insert in 'foo' with
default value:
# insert into foo(explication) values ('Because is in love');
But, what about 'v_foo'? If I make:
# insert into v_foo(explication) values ('Because have not slept');
I don't get default values properly because insert rule is forcing null
values. In fact, in this example I don't get nothing except an error for
trying to insert null value in primary key field.
Is there any way of resolving this problem?. Perhaps NEW might pass a
'default' value when it doesn't receive any data? have I lost some
important concept?...
Thanks.
David
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
>>
>> ---------------------------(end of
>> broadcast)---------------------------
>> TIP 4: Don't 'kill -9' the postmaster
>>
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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?
--
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