Passing a record as function argument PL/pgSQL - postgresql

Question

First I am really new to pl/pgsql. Need it for a project.
I am stuck with this (simplified) problem.
My db schema has a n to m relationship (author, books, author_books)
Now I want to have a pl/psgsql function insert_book. (I do know that all authors are definitely already in the author table, so I just want to pass their primary keys).
This function outline is what I have in mind.
create or replace function insert_book(book_to_insert book, authors integer[])
returns void as $$
begin
-- insert book into table books
-- for each author add an entry to author_books table
end;
$$ language plpgsql;
As arguments I thought to pass a record of type book and the authors that wrote it. But how exactly would this work? I googled quite a bit and can't seem to figure this out...
Question 1: Is the function outline "correct"/does it make sense?
Question 2: How to insert record book into table book? Do I have to go over all fields of book (title, isbn, publisher,...) and add them to an INSERT INTO statement or is there a "smarter" way?
Question 3: How would I call my function insert_book? I found this example here (http://dbaspot.com/postgresql/206142-passing-record-function-argument-pl-pgsql.html), but that doesn't really help me. For testing purposes I am using the shell, but later on we will use Java with JDBC.
Thank you very much for your help.

Answer 1

Using unnest() and a data-modifying CTE (requires Postgres 9.1 or later), this can be a simple SQL query:
WITH x AS (SELECT '(1,foo_book)'::book AS _book
, '{1,2,3}'::int[] AS _authors)
, y AS (
INSERT INTO book -- no column list, correct due to composite type
SELECT (x._book).*
FROM x
RETURNING book_id
)
INSERT INTO author_book (book_id, author_id)
SELECT y.book_id, unnest(x._authors)
FROM x,y; -- CROSS JOIN ok, only 1 row for x and y
The first CTE x is just for simplified data input and not strictly needed.
SQL Fiddle.
As to your questions:
Question 1: Is the function outline "correct"/does it make sense?
Might be easier to pass base types instead of the composite type book, but it is a perfectly valid approach. You have to know your way around the syntax for complex types, though. For instance, note the parenthesis around the name in my example: (x._book).*.
A plpgsql function could look like this:
CREATE OR REPLACE FUNCTION f_insert_book(_book book, _authors integer[])
RETURNS void AS
$func$
BEGIN
WITH y AS (
INSERT INTO book b
SELECT (_book).*
RETURNING b.book_id
)
INSERT INTO author_book (book_id, author_id)
SELECT y.book_id, unnest(_authors)
FROM y;
END
$func$ LANGUAGE plpgsql;
Question 2: How to insert record book into table book? (...) or is there a "smarter" way?
The smarter way is to decompose the composite type with (variable_name).*.
As the type is guaranteed to match the table (being derived from it), this is one of the rare cases, where it is perfectly ok, not to provide a column list for the INSERT command in persisted code.
Question 3: How would I call my function insert_book? ...
SELECT f_insert_book('(1,foo_book)'::book, '{1,2,3}'::int[]);
Within other plpgsql functions, use PERFORM instead of SELECT if you don't provide a target (INTO foo) for the (non-existing) results.

Answer 2

Passing JSON datatype (Postgresql 9.2 or higher):
CREATE OR REPLACE FUNCTION f_insert_book(_book json, _authors json)
RETURNS void AS
$$
BEGIN
-- insert book into table books
Insert into books values select * from json_populate_recordset(null:book, _book);
-- for each author add an entry to author_books table
Insert into authors values select * from json_populate_recordset(null:authors, _authors);
end;
$$ language plpgsql;