Rule or trigger for replacing view insert - postgresql

Question

I have an updatable postgres view which exposes a person table. The view hides some private data, such as email. When inserting I want users to be able to insert values for that private data. Would it be better to use a rule or a trigger to gain this functionality?
After some testing it seems like I can't use a trigger to insert to columns not defined in the view.

Answer 1

One possible way is to use privileges instead of view to expose subset of columns.
For example, given the table
create table person(
first_name text,
last_name text,
email text
);
you can grant the following privileges to a user:
grant select(first_name, last_name) on person to someuser;
grant insert on person to someuser;
And this is how it works:
postgres=> insert into person values('Foo','Bar','foo#bar.com');
INSERT 0 1
postgres=> select * from person;
ERROR: permission denied for relation person
postgres=> select first_name, last_name from person;
first_name | last_name
------------+-----------
Foo | Bar
(1 row)
Of course, it is only possible on "per user" basis.
Another way is to use function defined as "security definer". This specifies that the function is to be executed with the privileges of the user that created it.
So you can define a function to insert data directly into the table; definer must have the insert privilege:
create function person_insert(first_name text, last_name text, email text)
returns void
security definer
as $$
insert into person(first_name, last_name, email) values ($1, $2, $3);
$$ language sql;
Then the other user can call it without having himself the insert privilege:
postgres=> insert into person(first_name, last_name, email) values ('foo', 'bar', 'foo#bar.com');
ERROR: permission denied for relation person
postgres=> select person_insert('foo','bar','foo#bar.com');
people_insert
---------------
(1 row)
postgres=> select * from person_view;
first_name | last_name
------------+-----------
Foo | Bar
(1 row)