class ActiveRecord::ConnectionAdapters::PostgreSQL::TableDefinition

# File activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb, line 127
def primary_key(name, type = :primary_key, options = {})
  return super unless type == :uuid
  options[:default] = options.fetch(:default, 'uuid_generate_v4()')
  options[:primary_key] = true
  column name, type, options
end

Defines the primary key field. Use of the native PostgreSQL UUID type is supported, and can be used by defining your tables as such:

create_table :stuffs, id: :uuid do |t|
  t.string :content
  t.timestamps
end

By default, this will use the +uuid_generate_v4()+ function from the uuid-ossp extension, which MUST be enabled on your database. To enable the uuid-ossp extension, you can use the enable_extension method in your migrations. To use a UUID primary key without uuid-ossp enabled, you can set the :default option to nil:

create_table :stuffs, id: false do |t|
  t.primary_key :id, :uuid, default: nil
  t.uuid :foo_id
  t.timestamps
end

You may also pass a different UUID generation function from uuid-ossp or another library.

Note that setting the UUID primary key default value to nil will require you to assure that you always provide a UUID value before saving a record (as primary keys cannot be nil). This might be done via the SecureRandom.uuid method and a before_save callback, for instance.