Question

Is there a way to specify a database level uniqueness constraint on a field in a Rails 3.1+ migration? I know ActiveRecord’s validates_uniqueness_of would work, but I’m curious to know if this can be specified elsewhere.

For example, in order to specify that the ‘login’ field should be unique in a migration such as …

class CreateUsers < ActiveRecord::Migration
  def change
    create_table :users do |t|
      t.string :name
      t.string :login

      t.timestamps
    end
  end
end

… I’d like to add an option like :unique => true.

There’s nothing mentioned in the Documentation so I assume that’s not a great place/way to do things, but does anyone know how this might be achieved (even if it’s manually added to the resulting schema)? Or is validates_uniqueness_of the preferred way to go?

Answer 1

You can add unique index so:

def change
  create_table :users do |t|
    t.string :name
    t.string :login

    t.timestamps
  end

  add_index :users, :login, :unique => true
end