Thread: typmod for custom type

I have created a custom type called my_numeric, which is roughly the same as the existing numeric type. I have declared
in,out, typmod_in, and typmod_out functions. I create a table like: 

CREATE TABLE test (col1 my_numeric(6, 3));

And then do \d test and can see that col1 is declared as (6, 3), which I think confirms that my typmod_in and
typmod_outfunction are correct. 

But when I do:

INSERT INTO test VALUES ('12.34');

It behaves as though the typmod parameter to my in function (PG_GETARG_INT32(2)) is passed in as -1. The docs
(http://www.postgresql.org/docs/9.3/static/sql-createtype.html)says of the arguments that "the third is the typmod of
thedestination column, if known (-1 will be passed if not).". 

Am I doing something wrong? Don't I need to know the typmod of the destination column so I can confirm that the format
ofthe string being passed in conforms to the type modifier specified (eg so I can reject '1234.5678' for col1 with an
overflowerror)? 

Thanks

James

On 02/16/2014 12:12 AM, James Harper wrote:
> I have created a custom type called my_numeric, which is roughly the same as the existing numeric type. I have
declaredin, out, typmod_in, and typmod_out functions. I create a table like: 
>
> CREATE TABLE test (col1 my_numeric(6, 3));
>
> And then do \d test and can see that col1 is declared as (6, 3), which I think confirms that my typmod_in and
typmod_outfunction are correct. 
>
> But when I do:
>
> INSERT INTO test VALUES ('12.34');
>
> It behaves as though the typmod parameter to my in function (PG_GETARG_INT32(2)) is passed in as -1. The docs
(http://www.postgresql.org/docs/9.3/static/sql-createtype.html)says of the arguments that "the third is the typmod of
thedestination column, if known (-1 will be passed if not).". 

The value above looks valid to me. So what about the behavior is strange?

>
> Am I doing something wrong? Don't I need to know the typmod of the destination column so I can confirm that the
formatof the string being passed in conforms to the type modifier specified (eg so I can reject '1234.5678' for col1
withan overflow error)? 

It would help to see the  actual code you used to create the new type,
for those that would be able to help.

>
> Thanks
>
> James
>
>
>


--
Adrian Klaver
adrian.klaver@gmail.com

James Harper <james.harper@bendigoit.com.au> writes:
> I have created a custom type called my_numeric, which is roughly the same as the existing numeric type. I have
declaredin, out, typmod_in, and typmod_out functions. I create a table like: 
> CREATE TABLE test (col1 my_numeric(6, 3));

> And then do \d test and can see that col1 is declared as (6, 3), which I think confirms that my typmod_in and
typmod_outfunction are correct. 

> But when I do:

> INSERT INTO test VALUES ('12.34');

> It behaves as though the typmod parameter to my in function
> (PG_GETARG_INT32(2)) is passed in as -1.

It might be.  In at least some cases the parser will generate a value as
unconstrained my_numeric and then expect to be able to cast that to the
constrained subtype.  Whether that's the case here or not, in general you
will need a length-coercion cast function to support a type like this.
IIRC, you can read about that in the CREATE CAST documentation.

            regards, tom lane