I'm not sure this directly applies as I do not know Rails or your exact requirement. But you indicated the desire to "get a collection of records from the DB"; so perhaps it will.
Postgres contains 2 tables in pg_catalog you need to join to get the collection values for a enum: pg_type and pg_enum as follows (where ENUM_NAME is replaced by the appropriate enum type name:
select t.typname,e.enumsortorder, e.enumlabel
from pg_type t
join pg_enum e
on (t.oid = e.enumtypid)
where t.typname = 'ENUM_NAME'
order by e.enumsortorder;
One difference I've notice is that in Postgres the associated numeric value is defined as Real, not as Integer. This is due to how the values are actually maintained. Example:
create type t_ord_stat as enum ('Ordered', 'Delivered', 'Billed', 'Complete', 'Canceled');
select e.enumsortorder, e.enumlabel
from pg_type t
join pg_enum e
on (t.oid = e.enumtypid)
where t.typname = 't_ord_stat'
order by e.enumsortorder;
alter type t_ord_stat add value 'Suppended: Out-of-Stock' after 'Ordered';
alter type t_ord_stat add value 'Suppended: Credit Check' before 'Suppended: Out-of-Stock' ;
alter type t_ord_stat add value 'Suppended: Customer Refused Delivery' before 'Billed';
select e.enumsortorder, e.enumlabel
from pg_type t
join pg_enum e
on (t.oid = e.enumtypid)
where t.typname = 't_ord_stat'
order by e.enumsortorder;
The above gives the actual numeric values underlying the enum string value (as column name indicates it's for sorting purpose). You could get a relative integer value with
select row_number() over() relative_seq, en.enumlabel
from (select e.enumsortorder, e.enumlabel
from pg_type t
join pg_enum e
on (t.oid = e.enumtypid)
where t.typname = 't_ord_stat'
order by e.enumsortorder) en;
I'll leave the actual conversion to Rails to you. Hope it helps.