diff --git a/db/migrate/20160817210627_create_versions.rb b/db/migrate/20160817210627_create_versions.rb new file mode 100644 index 000000000..074d83f44 --- /dev/null +++ b/db/migrate/20160817210627_create_versions.rb @@ -0,0 +1,80 @@ +# This migration creates the `versions` table, the only schema PT requires. +# All other migrations PT provides are optional. +class CreateVersions < ActiveRecord::Migration[5.1] + # Class names of MySQL adapters. + # - `MysqlAdapter` - Used by gems: `mysql`, `activerecord-jdbcmysql-adapter`. + # - `Mysql2Adapter` - Used by `mysql2` gem. + MYSQL_ADAPTERS = [ + "ActiveRecord::ConnectionAdapters::MysqlAdapter", + "ActiveRecord::ConnectionAdapters::Mysql2Adapter" + ].freeze + + # The largest text column available in all supported RDBMS is + # 1024^3 - 1 bytes, roughly one gibibyte. We specify a size + # so that MySQL will use `longtext` instead of `text`. Otherwise, + # when serializing very large objects, `text` might not be big enough. + TEXT_BYTES = 1_073_741_823 + + def change + create_table :versions, versions_table_options do |t| + t.string :item_type, item_type_options + t.integer :item_id, null: false + t.string :event, null: false + t.string :whodunnit + t.text :object, limit: TEXT_BYTES + + # Known issue in MySQL: fractional second precision + # ------------------------------------------------- + # + # MySQL timestamp columns do not support fractional seconds unless + # defined with "fractional seconds precision". MySQL users should manually + # add fractional seconds precision to this migration, specifically, to + # the `created_at` column. + # (https://dev.mysql.com/doc/refman/5.6/en/fractional-seconds.html) + # + # MySQL users should also upgrade to rails 4.2, which is the first + # version of ActiveRecord with support for fractional seconds in MySQL. + # (https://github.com/rails/rails/pull/14359) + # + t.datetime :created_at + end + add_index :versions, [:item_type, :item_id] + end + + private + + # MySQL 5.6 utf8mb4 limit is 191 chars for keys used in indexes. + # See https://github.com/airblade/paper_trail/issues/651 + def item_type_options + opt = { null: false } + opt[:limit] = 191 if mysql? + opt + end + + def mysql? + MYSQL_ADAPTERS.include?(connection.class.name) + end + + # Even modern versions of MySQL still use `latin1` as the default character + # encoding. Many users are not aware of this, and run into trouble when they + # try to use PaperTrail in apps that otherwise tend to use UTF-8. Postgres, by + # comparison, uses UTF-8 except in the unusual case where the OS is configured + # with a custom locale. + # + # - https://dev.mysql.com/doc/refman/5.7/en/charset-applications.html + # - http://www.postgresql.org/docs/9.4/static/multibyte.html + # + # Furthermore, MySQL's original implementation of UTF-8 was flawed, and had + # to be fixed later by introducing a new charset, `utf8mb4`. + # + # - https://mathiasbynens.be/notes/mysql-utf8mb4 + # - https://dev.mysql.com/doc/refman/5.5/en/charset-unicode-utf8mb4.html + # + def versions_table_options + if mysql? + { options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci" } + else + {} + end + end +end