Add a Postgres array column in Rails 3

While migrations in Rails 3 don’t have built-in support for Postgres array columns, its still possible to add an array column in a migration using SQL. Here’s how. First, generate a migration

bundle exec rails g migration AddEnabledFeaturesToAccounts

Modify the migration to something like

class AddEnabledFeaturesToAccounts < ActiveRecord::Migration
  def up
    execute <<-SQL
ALTER TABLE accounts ADD COLUMN enabled_features character varying(255)[] DEFAULT '{}';
SQL
  end
end

The migration above adds a string array column. If you’d like to add an integer array column, change the SQL in the migration to add an integer array column

ALTER TABLE tickets ADD COLUMN cached_label_ids int[] DEFAULT '{}';

In case the table you’re adding the column to is huge, you may want to set the column default in a separate SQL statement to prevent the ADD COLUMN statement from locking the table for minutes (or even hours)

class AddEnabledFeaturesToAccounts < ActiveRecord::Migration
  def up
    execute <<-SQL
ALTER TABLE accounts ADD COLUMN enabled_features character varying(255)[];
SQL
   execute <<-SQL
ALTER TABLE accounts ALTER COLUMN enabled_features SET DEFAULT '{}';
SQL
  end
end