Adding a sequence to a migration

Rails
1

I want a field in my table to be a sequence that is not the id of the
record. Something like

create_table :foo do |t|
…
t.sequence :seq
…
end

Is there a clean way of doing this in migrations or will I end up
having to hack something. Like having an integer field and copying in
the id in an after_create filter?

2

What database are you using? I’m not aware of a “sequence” data type.

3

PostgreSQL has them, as do most DBs. This is where the ids come from.

4

Yes, in PostgrSQL you would create an integer column and assign a
sequence to it. I don’t know for sure but I expect that you cam do
something similar with other databases. I was wondering if this had
been abstracted away in ar

5

It’s very definitely abstracted away in migrations. You write one
basic migration, and the database adapter you’ve chosen takes care of
these implementation details for you. I can use the same migration on
my Mac with SQLite and on Heroku with PostgreSQL. No changes needed.

Walter

6

Not quite. The id column is just an integer column.

On MySQL, the id column is an integer column with auto_increment set.

On PostgreSQL, it’s still an integer column, but rails also attaches a
sequence object to it.

Are you just looking to create another integer column that is auto
incremented?