Question

I am developing a framework that dynamically creates tables for contents storage on PostgreSQL 9.1. One of the API functions allows caller to save a new contents entry by specifying all fields within a given object (say, web form). In order to receive a set of fields framework creates a composite type.

Consider the following code:

CREATE SEQUENCE seq_contents MINVALUE 10000;
CREATE TABLE contents (
    content_id      int8        not null,
    is_edited       boolean     not null default false,
    is_published    boolean     not null default false,
    "Input1"        varchar(60),
    "CheckBox1"     int2,
    "TheBox"        varchar(60),
    "Slider1"       varchar(60)
);
CREATE TYPE "contentsType" AS (
    "Input1"        varchar(60),
    "CheckBox1"     int2,
    "TheBox"        varchar(60),
    "Slider1"       varchar(60)
);
CREATE OR REPLACE FUNCTION push(in_all anyelement) RETURNS int8 AS $push$
DECLARE
    _c_id   int8;
BEGIN
    SELECT nextval('seq_contents') INTO _c_id;

    EXECUTE $$INSERT INTO contents
    SELECT a.*, b.*
      FROM (SELECT $1, true, false) AS a,
           (SELECT $2.*) AS b$$ USING _c_id, in_all;

    RETURN _c_id;
END;
$push$ LANGUAGE plpgsql;

Now, in order to call this function I have to add explicit cast, like this:

SELECT push(('input1',1,'thebox','slider1')::"contentsType");

Is there a way to avoid explicit cast? As I would like external callers not to deal with casts, i.e. hide the logic behind the PostgreSQL functions. Currently I have such error:

SELECT push(('input1',1,'thebox','slider1'));
ERROR:  PL/pgSQL functions cannot accept type record
CONTEXT:  compilation of PL/pgSQL function "push" near line 1

Answer 1

Have you considered passing the record variable as its text representation?
In theory, every record variable can be cast to and from text with the normal CAST operator.

Here is the function modified so that in_all has type text and gets casted to "contentsType" in the USING clause:

CREATE OR REPLACE FUNCTION push(in_all text) RETURNS int8 AS $push$
DECLARE
    _c_id   int8;
BEGIN
    SELECT nextval('seq_contents') INTO _c_id;

    EXECUTE $$INSERT INTO contents
    SELECT a.*, b.*
      FROM (SELECT $1, true, false) AS a,
           (SELECT $2.*) AS b$$ USING _c_id, in_all::"contentsType";

    RETURN _c_id;
END;
$push$ LANGUAGE plpgsql;

Then it can be called like this (no explicit reference to the type)

select push( '(input1,1,thebox,slider1)' );

or like that (explicit record casted to text)

SELECT push(('input1',1,'thebox','slider1')::"contentsType"::text);

That would work not just with “contentsType”, but any other record type, assuming the function is able to convert it back to that type.

Also in plpgsql, I assume this should work as well:

   ret := push(r::text);

when r is a record variable.