---
pg_extension_name: pg_role_fkey_trigger_functions
pg_extension_version: 0.11.7
pg_readme_generated_at: 2023-05-13 15:24:03.458634+01
pg_readme_version: 0.6.3
---

# The `pg_role_fkey_trigger_functions` extension for PostgreSQL

The `pg_role_fkey_trigger_functions` PostgreSQL extension offers a
bunch of trigger functions to help establish and/or maintain referential
integrity for columns that reference PostgreSQL `ROLE` `NAME`s.

`pg_role_fkey_trigger_functions` contains two trigger functions
which can be applied as a table `CONSTRAINT TRIGGER`:

1. `enforce_fkey_to_db_role()` _enforces_ referential integrity by getting angry
   when you try to `INSERT` or `UPDATE` a row value that is not an existing
   `ROLE`.
2. `maintain_referenced_role()` _establishes_ referential integrity by
   `CREATE`ing, `ALTER`ing, and `DROP`ing `ROLE`s to stay in sync with the
   value(s) in the column(s) being watched by the trigger function.

Thus:

1. `enforce_fkey_to_db_role()` works very much like foreign keys normally works;
   while
2. `maintain_referenced_role()` works exactly in the opposite direction that
   foreign keys normally work.

There is also a third trigger function, to maintain role inter-relationships:
`grant_role_in_column1_to_role_in_column2()`.

See the documentation for the
[`grant_role_in_column1_to_role_in_column2()`](#function-grant_role_in_column1_to_role_in_column2)
trigger function for an example that builds on all 3 trigger functions.

## The origins of the `pg_role_fkey_trigger_functions` extension

`pg_role_fkey_trigger_functions`, together with quite a sizeable bunch of other
PostgreSQL extensions, originated from the stables of the super-scalable
[FlashMQ](https://www.flashmq.com) managed MQTT hosting platform.  Its author,
responsible for the PostgreSQL backend of flashmq.com, found that a lot of the
Postgres functionality that started within the walls of that project deserved
wider exposure, even if just to make it easier for him and his colleagues to
reuse their craftwork across different projects.

And public release turns out to improve discipline:

- around the polishing of rough edges;
- around documentation completeness and up-to-dateness; and
- around keeping the number of interdependencies to a minimum (thus improving
  the architecture of the system using those extensions).

## Authors and contributors

* [Rowan](https://www.bigsmoke.us/) originated this extension in 2022 while
  developing the PostgreSQL backend for the [FlashMQ SaaS MQTT cloud
  broker](https://www.flashmq.com/).  Rowan does not like to see himself as a
  tech person or a tech writer, but, much to his chagrin, [he
  _is_](https://blog.bigsmoke.us/category/technology). Some of his chagrin
  about remaining stuck in the IT industry for too long he poured into a book:
  [_Why Programming Still Sucks_](https://www.whyprogrammingstillsucks.com/).
  Much more than a “tech bro”, he identifies as a garden gnome, fairy and ork
  rolled into one, and his passion is really to [regreen and reenchant his
  environment](https://sapienshabitat.com/).  One of his proudest achievements
  is to be the third generation ecological gardener to grow the wild garden
  around his beautiful [family holiday home in the forest of Norg, Drenthe,
  the Netherlands](https://www.schuilplaats-norg.nl/) (available for rent!).

## Object reference

### Routines

#### Function: `enforce_fkey_to_db_role()`

The `enforce_fkey_to_db_role()` trigger function is meant to be used for constraint triggers that raise a `foreign_key_violation` exception when you are trying to `INSERT` or `UPDATE` a value in the given column that is not a valid `ROLE` name.

`enforce_fkey_to_db_role()` takes one argument: the name of a column that is to
be treated as a foreign key to a database `ROLE`.

The following example establishes a constraint trigger such that you can only
set values for the `row_owner_role` column that are valid row names; anything
else will cause a `foreign_key_violation` to be raised:

```sql
create table test__tbl (
    id int
        primary key,
    row_owner_role name
        not null unique
);

create constraint trigger row_owner_role_must_exist
    after insert or update on test__tbl
    for each row
    execute function enforce_fkey_to_db_role('row_owner_role');
```

Sadly, it is (presently, with PostgreSQL 15) not possible to provide support
for `ON DELETE` and `ON UPDATE` options because PostgreSQL event triggers do
not catch DDL commands that `CREATE`, `ALTER`, and `DROP` roles.  Otherwise, we
could have an event trigger that also gets upset if you invalidate the FK role
relationship _after_ `INSERT`ing or `UPDATE`ing a initially valid `ROLE` name.

Function return type: `trigger`

#### Function: `grant_role_in_column1_to_role_in_column2()`

 The `grant_role_in_column1_to_role_in_column2()` trigger function is useful if you have a table with (probably auto-generated) role names that need to be members of each other.

`grant_role_in_column1_to_role_in_column2()` requires at least 2 arguments: argument 1 will contain the name of the column that will contain the role name which the role in the column of the second argument will be automatically made a member of.

If you want the old `GRANT` to be `REVOKE`d `ON UPDATE`, use the companion trigger function: `revoke_role_in_column1_from_role_in_column2()`.

Here's a full example, that also incorporates the other two trigger functions packaged into this extension:

```sql
create role customers;

create table test__customer (
    account_owner_role name
        primary key
        default 'user_' || gen_random_uuid()::text,
    account_manager_role name
        not null
);

create constraint trigger account_manager_role_fkey
    after insert or update to test__customer
    for each row
    execute function enforce_fkey_to_db_role('account_manager_role');

create trigger account_owner_role_fkey
    after insert or update or delete to test__customer
    for each row
    execute function maintain_referenced_role(
        'account_owner_role', 'IN ROLE customers'
    );

create trigger grant_owner_impersonation_to_account_manager
    after insert to test__customer
    for each row
    execute function grant_role_in_column1_to_role_in_column2(
        'account_owner_role', 'account_manager_role'
    );
```

See the `test__pg_role_fkey_trigger_functions()` procedure for a more extensive example.

Function return type: `trigger`

Function attributes: `SECURITY DEFINER`

#### Function: `maintain_referenced_role()`

The `maintain_referenced_role()` trigger function performs an `CREATE`, `ALTER`, or `DROP ROLE`, depending on (changes to) the column value which must point to a valid `ROLE` name.

`maintain_referenced_role()` takes at least one argument: the name of the
column (of type `NAME`) in which the `ROLE` name will be stored.

Additionally, `maintain_referenced_role()` can take a second argument: the
options which will be passed to the `CREATE` and `ALTER ROLE` commands exeuted
by this function.

This trigger function is meant for roles that are to be dynamically created,
altered and dropped, not for verifying the relational integrity of existing
roles; see `enforce_fkey_to_db_role()` for the latter.

The following example will first make `test__owner` pop into existence on
`INSERT`, then be renamed automaticall to `test__new_owner` on `UPDATE` and
finally dropped again, triggered by the `DELETE`.:

```sql
create table test__tbl (
    owner_role name
);

create trigger maintain_owner_role
    after insert or update on test__tbl
    for each row
    execute function maintain_referenced_role('owner_role', 'WITH NOLOGIN');

insert into test__tbl (owner_role)
    values ('test__owner');

update test__tbl
    set owner_role = 'test__new_owner';

delete from test__tbl
    where rolname = 'test__new_owner';
```

Function return type: `trigger`

Function attributes: `SECURITY DEFINER`

Function-local settings:

  *  `SET search_path TO pg_catalog`

#### Function: `pg_role_fkey_trigger_functions_meta_pgxn()`

Returns the JSON meta data that has to go into the `META.json` file needed for PGXN—PostgreSQL Extension Network—packages.

The `Makefile` includes a recipe to allow the developer to: `make META.json` to
refresh the meta file with the function's current output, including the
`default_version`.

And indeed, `pg_role_fkey_trigger_functions` can be found on the
[PGXN—PostgreSQL Extension Network](https://pgxn.org/):
https://pgxn.org/dist/pg_role_fkey_trigger_functions/

Function return type: `jsonb`

Function attributes: `STABLE`

#### Function: `pg_role_fkey_trigger_functions_readme()`

This function utilizes the `pg_readme` extension to generate a thorough README for this extension, based on the `pg_catalog` and the `COMMENT` objects found therein.

Function return type: `text`

Function-local settings:

  *  `SET search_path TO role_fkey_trigger_functions, pg_temp`
  *  `SET pg_readme.include_view_definitions TO true`
  *  `SET pg_readme.include_routine_definitions_like TO {test__%}`

#### Function: `revoke_role_in_column1_from_role_in_column2()`

Use this trigger function, in concert with `grant_role_in_column1_to_role_in_column2()`, if, `ON UPDATE`, you also want to `REVOKE` the old permissions granted earlier by `grant_role_in_column1_to_role_in_column2()`.

**Beware:** This function cannot read your mind and thus will not be aware if there is still another relation that depends on the role in column 2 remaining a member of the role in column 1. As always: use at your own peril.

Function return type: `trigger`

Function attributes: `SECURITY DEFINER`

#### Procedure: `test_dump_restore__maintain_referenced_role (text)`

Procedure arguments:

| Arg. # | Arg. mode  | Argument name                                                     | Argument type                                                        | Default expression  |
| ------ | ---------- | ----------------------------------------------------------------- | -------------------------------------------------------------------- | ------------------- |
|   `$1` |       `IN` | `test_stage$`                                                     | `text`                                                               |  |

Procedure-local settings:

  *  `SET search_path TO role_fkey_trigger_functions, pg_temp`
  *  `SET plpgsql.check_asserts TO true`
  *  `SET pg_readme.include_this_routine_definition TO true`

```sql
CREATE OR REPLACE PROCEDURE role_fkey_trigger_functions.test_dump_restore__maintain_referenced_role(IN "test_stage$" text)
 LANGUAGE plpgsql
 SET search_path TO 'role_fkey_trigger_functions', 'pg_temp'
 SET "plpgsql.check_asserts" TO 'true'
 SET "pg_readme.include_this_routine_definition" TO 'true'
AS $procedure$
declare
    _inserted_account_owner_role name;
begin
    assert test_stage$ in ('pre-dump', 'post-restore');

    if test_stage$ = 'pre-dump' then
        create role test__customer_group;
        create role test__account_manager;

        create table test__customer (
            account_owner_role name
                primary key
                default 'user_' || gen_random_uuid()::text,
            account_manager_role name
                not null
        );

        create trigger account_owner_role_fkey
            after insert or update or delete on test__customer
            for each row
            execute function maintain_referenced_role(
                'account_owner_role', 'IN ROLE test__customer_group'
            );

        create trigger account_manager_role_fkey
            after insert or update on test__customer
            for each row
            execute function enforce_fkey_to_db_role(
                'account_manager_role'
            );

        insert into test__customer
            (account_owner_role, account_manager_role)
        values
            (default, 'test__account_manager'::regrole)
        returning
            account_owner_role
        into
            _inserted_account_owner_role
        ;

        assert exists (select from pg_roles where rolname = _inserted_account_owner_role),
            'The role should have been created by the maintain_referenced_role() trigger function.';

    elsif test_stage$ = 'post-restore' then
        assert (select count(*) from test__customer) = 1,
            'Records should have been recreated without crashing.';

        _inserted_account_owner_role := (select account_owner_role from test__customer);

        -- Now, let's lazily pretend that the database has been dropped and recreated
        truncate table test__customer;  -- This should not trigger the `account_owner_role_fkey` trigger.

        insert into test__customer
            (account_owner_role, account_manager_role)
        values
            (_inserted_account_owner_role, 'test__account_manager'::regrole)
        ;
    end if;
end;
$procedure$
```

#### Procedure: `test__pg_role_fkey_trigger_functions()`

Procedure-local settings:

  *  `SET search_path TO role_fkey_trigger_functions, pg_temp`
  *  `SET plpgsql.check_asserts TO true`
  *  `SET pg_readme.include_this_routine_definition TO true`

```sql
CREATE OR REPLACE PROCEDURE role_fkey_trigger_functions.test__pg_role_fkey_trigger_functions()
 LANGUAGE plpgsql
 SET search_path TO 'role_fkey_trigger_functions', 'pg_temp'
 SET "plpgsql.check_asserts" TO 'true'
 SET "pg_readme.include_this_routine_definition" TO 'true'
AS $procedure$
declare
    _inserted_account_owner_role name;
    _updated_account_owner_role name;
begin
    create role test__customer_group;
    create role test__account_manager;
    create role test__new_account_manager;

    create table test__customer (
        account_owner_role name
            primary key
            default 'user_' || gen_random_uuid()::text,
        account_manager_role name
            not null
    );

    create constraint trigger tg1_account_manager_role_fkey
        after insert or update on test__customer
        for each row
        execute function enforce_fkey_to_db_role('account_manager_role');

    create trigger tg2_account_owner_role_fkey
        after insert or update or delete on test__customer
        for each row
        execute function maintain_referenced_role(
            'account_owner_role', 'IN ROLE test__customer_group'
        );

    create trigger tg3_grant_owner_impersonation_to_account_manager
        after insert on test__customer
        for each row
        execute function grant_role_in_column1_to_role_in_column2(
            'account_owner_role', 'account_manager_role'
        );

    create trigger tg4_revoke_owner_impersonation_from_old_account_manager
        after update on test__customer
        for each row
        when (NEW.account_manager_role is distinct from OLD.account_manager_role)
        execute function revoke_role_in_column1_from_role_in_column2(
            'account_owner_role', 'account_manager_role'
        );

    create trigger tg5_grant_owner_impersonation_to_new_account_manager
        after update on test__customer
        for each row
        when (NEW.account_manager_role is distinct from OLD.account_manager_role)
        execute function grant_role_in_column1_to_role_in_column2(
            'account_owner_role', 'account_manager_role'
        );

    <<insert_invalid_role_reference>>
    begin
        insert into test__customer
            values (default, 'test__account_manager_that_doesnt_exist');
        raise assert_failure
            using message = 'The trigger function should have gotten upset about the missing `ROLE`.';
    exception
        when foreign_key_violation then
            assert sqlerrm = 'Unknown database role: test__account_manager_that_doesnt_exist';
    end;

    <<insert_existing_role>>
    begin
        create role test__preexisting_user;
        insert into test__customer
            values ('test__preexisting_user', 'test__account_manager'::regrole);
        raise assert_failure
            using message = 'The trigger function should have gotten upset about the existing `ROLE`.';
    exception
        when integrity_constraint_violation then
            assert sqlerrm = 'Role test__preexisting_user already exists.',
                sqlerrm;
    end;

    insert into test__customer
        (account_owner_role, account_manager_role)
    values
        (default, 'test__account_manager'::regrole)
    returning
        account_owner_role
    into
        _inserted_account_owner_role
    ;

    assert exists (select from pg_roles where rolname = _inserted_account_owner_role),
        'The role should have been created by the maintain_referenced_role() trigger function.';

    assert pg_has_role(_inserted_account_owner_role, 'test__customer_group', 'USAGE'),
        'The new role should have became a member of the "test__customer_group".';

    assert pg_has_role('test__account_manager'::regrole, _inserted_account_owner_role, 'USAGE'),
        'The account manager should have gotten access to the new owner role by action of the'
        ' grant_role_in_column1_to_role_in_column2() trigger function';

    <<set_invalid_role_reference>>
    begin
        update test__customer
            set account_manager_role = 'test__invalid_account_manager';
        raise assert_failure
            using message = 'The trigger function should have gotten upset about the missing `ROLE`.';
    exception
        when foreign_key_violation then
            assert sqlerrm = 'Unknown database role: test__invalid_account_manager';
    end;

    -- Dummy update, to check for rogue trigger behaviour
    update test__customer
        set account_manager_role = account_manager_role;

    _updated_account_owner_role := 'test__custom_user_name';
    update test__customer
        set account_owner_role = _updated_account_owner_role;

    assert exists (select from pg_roles where rolname = _updated_account_owner_role);
    assert not exists (select from pg_roles where rolname = _inserted_account_owner_role);
    assert pg_has_role(_updated_account_owner_role, 'test__customer_group', 'USAGE');
    assert pg_has_role('test__account_manager', _updated_account_owner_role, 'USAGE');

    update test__customer
        set account_manager_role = 'test__new_account_manager'::regrole;
    assert not pg_has_role('test__account_manager', _updated_account_owner_role, 'USAGE'),
        'The old account manager should have lost impersonation rights on this customer.';
    assert pg_has_role('test__new_account_manager', _updated_account_owner_role, 'USAGE'),
        'The new account manager should have gotten impersonation rights on this customer.';

    delete from test__customer;
    assert not exists (select from pg_roles where rolname = _updated_account_owner_role);

    raise transaction_rollback;
exception
    when transaction_rollback then
end;
$procedure$
```

## Colophon

This `README.md` for the `pg_role_fkey_trigger_functions` extension was automatically generated using the [`pg_readme`](https://github.com/bigsmoke/pg_readme) PostgreSQL extension.