How do I add a check constraint in a Rails migration?

Rails migration does not provide any way to add Constraints, but you can still do it via migration but by passing actual SQL to execute()

Create Migration file:

ruby script/generate Migration AddConstraint

Now, in the migration file:

class AddConstraint < ActiveRecord::Migration
  def self.up
    execute "ALTER TABLE table_name ADD CONSTRAINT check_constraint_name CHECK (check_column_name IN (1, 2, 3) )"
  end

  def self.down
    execute "ALTER TABLE table_name DROP CONSTRAINT check_constraint_name"
  end
end