How to disable PK changes in Postgres?-CodePudding

How do I disable PK changes in my db? Is it possible?

For example, I have this table:

user
id name email password ...
1  Alex ...   ...
2  Mark ...   ...

How to disable the possibility of changing user.id?

CodePudding user response：

You can use the database reference mechanism. Create a dummy table that references the column you want to protect and revoke the access privilege to this table for other users. Example:

create table users(
    id int primary key,
    name text);
insert into users values
(1, 'John');

create table users_restrict(
    id int references users);
insert into users_restrict 
values (1);

The default mode of the reference is to restrict deletes or updates:

update users set
    id = 2
where id = 1;
    
ERROR:  update or delete on table "users" violates foreign key constraint "users_restrict_id_fkey" on table "users_restrict"
DETAIL:  Key (id)=(1) is still referenced from table "users_restrict".

Alternatively, you can define a trigger to abandon modifications you do not want, e.g.

create or replace function protect_users_id()
returns trigger language plpgsql as $$
begin
    if old.id <> new.id then
        raise exception 'Cannot change users.id';
    end if;
end $$;

create trigger protect_users_id
before update on users
for each row execute procedure protect_users_id();

Test it in db<>fiddle.