Rails 5—How to add UUID column

Question

There doesn't seem to be much documentation on UUIDs in Rails 5. All I've found is this code:

create_table :users, id: :uuid do |t|
  t.string :name
end

That works great if you're creating a table, but what if you're updating an already-existing table?

How do you add a UUID column to a table?

Answer 1

To migrate from default id to use uuid, try writing migration like this:

class ChangeProjectsPrimaryKey < ActiveRecord::Migration
   def change
     add_column :projects, :uuid, :uuid, default: "uuid_generate_v4()", null: false

     change_table :projects do |t|
       t.remove :id
       t.rename :uuid, :id
     end

     execute "ALTER TABLE projects ADD PRIMARY KEY (id);"
   end
 end

Answer 2

Here's how to add a uuid column to an existing Rails table.

class AddUuidToContacts < ActiveRecord::Migration[5.1]
  def change
     enable_extension 'uuid-ossp' # => http://theworkaround.com/2015/06/12/using-uuids-in-rails.html#postgresql
     add_column :contacts, :uuid, :uuid, default: "uuid_generate_v4()", null: false
     execute "ALTER TABLE contacts ADD PRIMARY KEY (uuid);"
  end
end

If you forget to add enable_extension 'uuid-ossp', you'll get these errors:

PG::UndefinedFunction: ERROR: function uuid_generate_v4() does not exist ActiveRecord::StatementInvalid: PG::UndefinedFunction: ERROR: function uuid_generate_v4() does not exist