primary_key

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 gen_random_uuid() function from the pgcrypto extension. As that extension is only available in PostgreSQL 9.4+, for earlier versions an explicit default can be set to use uuid_generate_v4() from the uuid-ossp extension instead:

create_table :stuffs, id: false do |t|
  t.primary_key :id, :uuid, default: "uuid_generate_v4()"
  t.uuid :foo_id
  t.timestamps
end

To enable the appropriate extension, which is a requirement, use the enable_extension method in your migrations.

To use a UUID primary key without any of the extensions, 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 custom stored procedure that returns a UUID or use a different UUID generation function from 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.

# File activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb, line 48
        def primary_key(name, type = :primary_key, **options)
          if type == :uuid
            options[:default] = options.fetch(:default, "gen_random_uuid()")
          end

          super
        end