How do I retroactively add a primary key to my table in rails?

Question

I've created a table without a primary key (:id => false), but now it has come back to bite my ass.

My app is already in production and I can't just drop it and recreate another one.

Is there a way to run a migration to add another auto increment primary key column to my table?

Answer 1

The command to add a primary key in a migration is:

add_column :my_table, :id, :primary_key

However, the wording of your question suggests that your table already has an auto-increment column. Unless I'm mistaken, there are several DBMS that do not allow more than one auto-increment column on a table.

If you DO already have an auto-increment column and you actually want to use that column as your primary key, just add the following to your model:

set_primary_key "my_existing_column"

Or in more recent versions of Rails:

self.primary_key = "my_existing_column"

In the case that you already have an auto-increment column and you can't use that as the primary key, you may be out of luck.

Answer 2

If for some reason you created a table with a custom id field, but forgot to set id as the primary key, you need to run a migration to create the primary key constraint. The following was tested against a PostgreSQL database:

class AddPrimaryKeyConstraintToFoobars < ActiveRecord::Migration   def up     execute "ALTER TABLE foobars ADD PRIMARY KEY (id);"   end    def down     execute "ALTER TABLE foobars DROP CONSTRAINT foobars_pkey;"   end end