Identity Type

How often do you run into a case like this?

 ```sql
create table users
(
    id serial primary key
);
create table orders
(
    id      serial primary key,
    user_id int not null references users (id)
);

select *
from users
         inner join orders on orders.id = users.id

--- Why is this not getting the right results? \o/
--- ooooh... it should have been `on orders.user_id = users.id`

In a simple case, it is usually easy to spot the problem. However, real operational queries tend to get a lot more complicated, with a lot of visual noise in them, and spotting subtle errors is hard.

omni_id solves exacly this problem by introduce custom types that are comparable to themselves but not other types (at least, not without explicit casting).

create table users
(
    id user_id primary key default user_id_nextval()
);
create table orders
(
    id      order_id primary key default order_id_nextval(),
    user_id user_id not null references users (id)
);

select *
from users
         inner join orders on orders.id = users.id

-- ERROR: operator does not exist: order_id = user_id
-- ^^^ this just saved us precious time

Usage

This extension defines a single function identity_type. In its most primitive form, it will just take a name of a new type and will create a bigint-backed type:

create extension omni_id;
-- CREATE EXTENSION
select identity_type('user_id');
-- identity_type 
-- ---------------
-- user_id

You can also select a different base integer type (smallint, int) and a few sequence-related options.

Parameter	Type	Description
type	regtype	Base type. bigint by default. int and smallint permitted, as well as their aliases, and uuid
sequence	text	Sequence name. Equal to <type>_seq by default
create_sequence	boolean	Should sequence be created? True by default. Meaningless for uuid base type.
increment	bigint	Sequence increment. Default set to 1
minvalue	bigint	Minimum value a sequence can generate. Default set to 1
maxvalue	bigint	Maximum value a sequence can generate. Default set to the maximum of the underlying type
cache	bigint	Enables sequence numbers to be preallocated and stored in memory for faster access
cycle	boolean	Wrap around when the maxvalue or minvalue has been reached by an ascending or descending sequence respectively
constructor	text	Name of the constructor function
create_constructor	boolean	Should constructor be created? True by default
operator_schema	boolean	Schema to create operators in. public by default
nextval	regproc	If not null, use this function (no arguments, returning base type) to make <type>_nextval()

identity_type will also create helper functions for the sequence: <type>_nextval(), <type>_currval() and <type>_setval(<type>, bool)

Constructor

When it is necessary to construct an identity type value, one can use a constructor function like this:

select user_id(1);