webdack-uuid_migration

Webdack::UuidMigration

This project is actively maintained. Please report issues and/or create pull requests if you face any issues.

There are plenty of tutorials around the web on how to use UUIDs with Rails. However, there is no reliable tutorial to help convert an in-production Rails application from Integer ids to UUIDs.

This gem has helper methods to convert Integer columns to UUIDs during migrations. It supports migrating primary key columns, relations, and polymorphic relations.

It is designed to be fast and is suitable for in-place migration of schema and data. It has been used in production since 2014.

This only supports PostgreSQL.

Documentation

http://www.rubydoc.info/gems/webdack-uuid_migration (The link may occasionally not work).

Installation

Add this line to your application's Gemfile:

    gem 'webdack-uuid_migration'

And then execute:

    $ bundle

Or install it yourself as:

    $ gem install webdack-uuid_migration

This gem is needed only during database migrations. Once the database has been migrated in all environments, this gem can safely be removed from your applications Gemfile.

Usage

• Put require 'webdack/uuid_migration/helpers' in your migration file.
• Enable 'pgcrypto' directly in Postgres database or by adding enable_extension 'pgcrypto' to your migration. If you want to generate random UUIDs, enable uuid-ossp as well.
• Use methods from {Webdack::UUIDMigration::Helpers} as appropriate.

Example:

    # You must explicitly require it in your migration file
    require 'webdack/uuid_migration/helpers'

    class UuidMigration < ActiveRecord::Migration
      def change
        reversible do |dir|
          dir.up do
            # Good idea to do the following, needs superuser rights in the database
            # Alternatively the extension needs to be manually enabled in the RDBMS
            enable_extension 'pgcrypto'

            primary_key_to_uuid :students

            primary_key_to_uuid :cities
            primary_key_to_uuid :sections
            columns_to_uuid :students, :city_id, :section_id
          end

          dir.down do
            raise ActiveRecord::IrreversibleMigration
          end
        end
      end
    end

By default, integer values are converted to UUID by padding 0's to the left. This makes it possible to retrieve old id in future. See Generating random UUIDs below to convert integer into random UUIDs using a seed.

See {Webdack::UUIDMigration::Helpers} for more details. {Webdack::UUIDMigration::Helpers} is mixed into {ActiveRecord::Migration}, so that all methods can directly be used within migrations.

Schema with Foreign Key References

Please see [https://github.com/kreatio-sw/webdack-uuid_migration/issues/4]

This function will only work with Rails 4.2 or newer.

To update a primary key and all columns referencing it please use {Webdack::UUIDMigration::Helpers#primary_key_and_all_references_to_uuid}. For example:

class MigrateWithFk < ActiveRecord::Migration
  def change
    reversible do |dir|
      dir.up do
        enable_extension 'pgcrypto'

        primary_key_and_all_references_to_uuid :cities
      end

      dir.down do
        raise ActiveRecord::IrreversibleMigration
      end
    end
  end
end

Internally it will query the database to find all tables & columns referring to this primary key as foreign keys and do the following:

• Drop all foreign key constraints referring to this primary key
• Convert the primary key to UUID
• Convert all referring columns to UUID
• Restore all foreign keys

Polymorphic references

Migrating Polymorphic references may get tricky if not all the participating entities are getting migrated to UUID primary keys. If only some of the referenced entities are getting migrated to use UUID primary keys please use the following steps:

• Change the corresponding _id to String type (at least VARCHAR(36)).
• Call polymorphic_column_data_for_uuid :table, :column, 'Entity1', 'Entity2', ...
• Note that :column in is without the _id.
• See {Webdack::UUIDMigration::Helpers#polymorphic_column_data_for_uuid}
• When all remaining references also gets migrated to UUID primary keys, call columns_to_uuid :table, :column_id

Example:

    # Student -- belongs_to :institution, :polymorphic => true
    # An institution is either a School or a College
    # College is migrated to use UUID as primary key
    # School uses Integer primary keys

    # Place the following in migration script
        primary_key_to_uuid :colleges
        change_column :students, :institution_id, :string
        polymorphic_column_data_for_uuid :students, :institution, 'College'

    # When School also gets migrated to UUID primary key
        primary_key_to_uuid :schools
        columns_to_uuid :students, :institution_id

    # See the rspec test case in spec folder for full example

Generating random UUIDs

You can provide a seed parameter with a valid UUID, which will be used to convert integers into random UUIDs using uuid_generate_v5. You will only be able to recover the old IDs in the future if you use the seed you used during the migration to generate a rainbow table.

Examples:

seed = SecureRandom.uuid

primary_key_to_uuid :colleges, seed: seed
columns_to_uuid :students, :institution_id, seed: seed
polymorphic_column_data_for_uuid :students, :institution, 'College', seed: seed
primary_key_and_all_references_to_uuid :cities: seed: seed

Note: Given a set of IDs (which are used, for example, as primary key in one table and foreign key in multiple tables), you will need to use the same seed in all method calls. Otherwise, the conversion will happen differently in each one of the tables, and the relations will be effectively lost. In general, it is adviced to use a different seed per ID set (primary key) to maintain data consistency and guarantee uniqueness across tables.

Compatibility

Works with Rails 4.2+, 5 & 6. It uses Rails 4's out-of-the-box UUID support for PostgreSQL.

Update to latest version (>=1.4.0) for using it with Ruby 3.

See https://travis-ci.org/kreatio-sw/webdack-uuid_migration for current build matrix.

To run the test suite:

# Update connection parameters in `spec/support/pg_database_helper.rb`.
# Postgres user must have rights to create/drop database and create extensions.
$ bundle exec rspec spec

Credits

• Users of the Gem
• Felix Bünemann for checking compatibility with Rails 4.1
• Nick Schwaderer Rails 5.2.x compatibility
• Kelsey Hannan Upgrading to pgcrypto
• Sébastien Dubois Ruby 3.0 compatibility
• Manuel Bustillo Alonso Random UUID support

Contributing

1. Fork it ( http://github.com/kreatio-sw/webdack-uuid_migration/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request