Version 6.0 - August 2019

Highlights in Rails 6.0:

  • Action Mailbox
  • Action Text
  • Parallel Testing
  • Action Cable Testing

These release notes cover only the major changes. To learn about various bug fixes and changes, please refer to the changelogs or check out the list of commits in the main Rails repository on GitHub.

Upgrading to Rails 6.0

If you’re upgrading an existing application, it’s a great idea to have good test coverage before going in. You should also first upgrade to Rails 5.2 in case you haven’t and make sure your application still runs as expected before attempting an update to Rails 6.0. A list of things to watch out for when upgrading is available in the Upgrading Ruby on Rails guide.

Major Features

Action Mailbox

Pull Request

Action Mailbox allows you to route incoming emails to controller-like mailboxes. You can read more about Action Mailbox in the Action Mailbox Basics guide.

Action Text

Pull Request

Action Text brings rich text content and editing to Rails. It includes the Trix editor that handles everything from formatting to links to quotes to lists to embedded images and galleries. The rich text content generated by the Trix editor is saved in its own RichText model that’s associated with any existing Active Record model in the application. Any embedded images (or other attachments) are automatically stored using Active Storage and associated with the included RichText model.

You can read more about Action Text in the Action Text Overview guide.

Parallel Testing

Pull Request

Parallel Testing allows you to parallelize your test suite. While forking processes is the default method, threading is supported as well. Running tests in parallel reduces the time it takes your entire test suite to run.

Action Cable Testing

Pull Request

Action Cable testing tools allow you to test your Action Cable functionality at any level: connections, channels, broadcasts.


Please refer to the Changelog for detailed changes.


  • Remove deprecated after_bundle helper inside plugins templates. (Commit)

  • Remove deprecated support to that uses the application class as argument of run. (Commit)

  • Remove deprecated environment argument from the rails commands. (Commit)

  • Remove deprecated capify! method in generators and templates. (Commit)

  • Remove deprecated config.secret_token. (Commit)


  • Deprecate passing Rack server name as a regular argument to rails server. (Pull Request)

  • Deprecate support for using HOST environment to specify server IP. (Pull Request)

  • Deprecate accessing hashes returned by config_for by non-symbol keys. (Pull Request)

Notable changes

  • Add an explicit option --using or -u for specifying the server for the rails server command. (Pull Request)

  • Add ability to see the output of rails routes in expanded format. (Pull Request)

  • Run the seed database task using inline Active Job adapter. (Pull Request)

  • Add a command rails db:system:change to change the database of the application. (Pull Request)

  • Add rails test:channels command to test only Action Cable channels. (Pull Request)

  • Introduce guard against DNS rebinding attacks. (Pull Request)

  • Add ability to abort on failure while running generator commands. (Pull Request)

  • Make Webpacker the default JavaScript compiler for Rails 6. (Pull Request)

  • Add multiple database support for rails db:migrate:status command. (Pull Request)

  • Add ability to use different migration paths from multiple databases in the generators. (Pull Request)

  • Add support for multi environment credentials. (Pull Request)

  • Make null_store as default cache store in test environment. (Pull Request)

Action Cable

Please refer to the Changelog for detailed changes.


  • Replace ActionCable.startDebugging() and ActionCable.stopDebugging() with ActionCable.logger.enabled. (Pull Request)


  • There are no deprecations for Action Cable in Rails 6.0.

Notable changes

  • Add support for the channel_prefix option for PostgreSQL subscription adapters in cable.yml. (Pull Request)

  • Allow passing a custom configuration to ActionCable::Server::Base. (Pull Request)

  • Add :action_cable_connection and :action_cable_channel load hooks. (Pull Request)

  • Add Channel::Base#broadcast_to and Channel::Base.broadcasting_for. (Pull Request)

  • Close a connection when calling reject_unauthorized_connection from an ActionCable::Connection. (Pull Request)

  • Convert the Action Cable JavaScript package from CoffeeScript to ES2015 and publish the source code in the npm distribution. (Pull Request)

  • Move the configuration of the WebSocket adapter and logger adapter from properties of ActionCable to ActionCable.adapters. (Pull Request)

  • Add an id option to the Redis adapter to distinguish Action Cable’s Redis connections. (Pull Request)

Action Pack

Please refer to the Changelog for detailed changes.


  • Remove deprecated fragment_cache_key helper in favor of combined_fragment_cache_key. (Commit)

  • Remove deprecated methods in ActionDispatch::TestResponse: #success? in favor of #successful?, #missing? in favor of #not_found?, #error? in favor of #server_error?. (Commit)


  • Deprecate ActionDispatch::Http::ParameterFilter in favor of ActiveSupport::ParameterFilter. (Pull Request)

  • Deprecate controller level force_ssl in favor of config.force_ssl. (Pull Request)

Notable changes

  • Change ActionDispatch::Response#content_type returning Content-Type header as it is. (Pull Request)

  • Raise an ArgumentError if a resource param contains a colon. (Pull Request)

  • Allow ActionDispatch::SystemTestCase.driven_by to be called with a block to define specific browser capabilities. (Pull Request)

  • Add ActionDispatch::HostAuthorization middleware that guards against DNS rebinding attacks. (Pull Request)

  • Allow the use of parsed_body in ActionController::TestCase. (Pull Request)

  • Raise an ArgumentError when multiple root routes exist in the same context without as: naming specifications. (Pull Request)

  • Allow the use of #rescue_from for handling parameter parsing errors. (Pull Request)

  • Add ActionController::Parameters#each_value for iterating through parameters. (Pull Request)

  • Encode Content-Disposition filenames on send_data and send_file. (Pull Request)

  • Expose ActionController::Parameters#each_key. (Pull Request)

  • Add purpose and expiry metadata inside signed/encrypted cookies to prevent copying the value of cookies into one another. (Pull Request)

  • Raise ActionController::RespondToMismatchError for conflicting respond_to invocations. (Pull Request)

  • Add an explicit error page for when a template is missing for a request format. (Pull Request)

  • Introduce ActionDispatch::DebugExceptions.register_interceptor, a way to hook into DebugExceptions and process the exception, before being rendered. (Pull Request)

  • Output only one Content-Security-Policy nonce header value per request. (Pull Request)

  • Add a module specifically for the Rails default headers configuration that can be explicitly included in controllers. (Pull Request)

  • Add #dig to ActionDispatch::Request::Session. (Pull Request)

Action View

Please refer to the Changelog for detailed changes.


  • Remove deprecated image_alt helper. (Commit)

  • Remove an empty RecordTagHelper module from which the functionality was already moved to the record_tag_helper gem. (Commit)


  • Deprecate ActionView::Template.finalize_compiled_template_methods with no replacement. (Pull Request)

  • Deprecate config.action_view.finalize_compiled_template_methods with no replacement. (Pull Request)

  • Deprecate calling private model methods from the options_from_collection_for_select view helper. (Pull Request)

Notable changes

  • Clear Action View cache in development only on file changes, speeding up development mode. (Pull Request)

  • Move all of the Rails npm packages into a @rails scope. (Pull Request)

  • Only accept formats from registered MIME types. (Pull Request, Pull Request)

  • Add allocations to the template and partial rendering server output. (Pull Request)

  • Add a year_format option to date_select tag, making it possible to customize year names. (Pull Request)

  • Add a nonce: true option for javascript_include_tag helper to support automatic nonce generation for a Content Security Policy. (Pull Request)

  • Add a action_view.finalize_compiled_template_methods configuration to disable or enable ActionView::Template finalizers. (Pull Request)

  • Extract the JavaScript confirm call to its own, overridable method in rails_ujs. (Pull Request)

  • Add a action_controller.default_enforce_utf8 configuration option to handle enforcing UTF-8 encoding. This defaults to false. (Pull Request)

  • Add I18n key style support for locale keys to submit tags. (Pull Request)

Action Mailer

Please refer to the Changelog for detailed changes.



  • Deprecate ActionMailer::Base.receive in favor of Action Mailbox. (Commit)

  • Deprecate DeliveryJob and Parameterized::DeliveryJob in favor of MailDeliveryJob. (Pull Request)

Notable changes

  • Add MailDeliveryJob for delivering both regular and parameterized mail. (Pull Request)

  • Allow custom email delivery jobs to work with the Action Mailer test assertions. (Pull Request)

  • Allow specifying a template name for multipart emails with blocks instead of using just the action name. (Pull Request)

  • Add perform_deliveries to payload of deliver.action_mailer notification. (Pull Request)

  • Improve the logging message when perform_deliveries is false to indicate that sending of emails was skipped. (Pull Request)

  • Allow calling assert_enqueued_email_with without block. (Pull Request)

  • Perform the enqueued mail delivery jobs in the assert_emails block. (Pull Request)

  • Allow ActionMailer::Base to unregister observers and interceptors. (Pull Request)

Active Record

Please refer to the Changelog for detailed changes.


  • Remove deprecated #set_state from the transaction object. (Commit)

  • Remove deprecated #supports_statement_cache? from the database adapters. (Commit)

  • Remove deprecated #insert_fixtures from the database adapters. (Commit)

  • Remove deprecated ActiveRecord::ConnectionAdapters::SQLite3Adapter#valid_alter_table_type?. (Commit)

  • Remove support for passing the column name to sum when a block is passed. (Commit)

  • Remove support for passing the column name to count when a block is passed. (Commit)

  • Remove support for delegation of missing methods in a relation to Arel. (Commit)

  • Remove support for delegating missing methods in a relation to private methods of the class. (Commit)

  • Remove support for specifying a timestamp name for #cache_key. (Commit)

  • Remove deprecated ActiveRecord::Migrator.migrations_path=. (Commit)

  • Remove deprecated expand_hash_conditions_for_aggregates. (Commit)


  • Deprecate mismatched case-sensitivity collation comparisons for uniqueness validator. (Commit)

  • Deprecate using class level querying methods if the receiver scope has leaked. (Pull Request)

  • Deprecate config.active_record.sqlite3.represent_boolean_as_integer. (Commit)

  • Deprecate passing migrations_paths to connection.assume_migrated_upto_version. (Commit)

  • Deprecate ActiveRecord::Result#to_hash in favor of ActiveRecord::Result#to_a. (Commit)

  • Deprecate methods in DatabaseLimits: column_name_length, table_name_length, columns_per_table, indexes_per_table, columns_per_multicolumn_index, sql_query_length, and joins_per_query. (Commit)

  • Deprecate update_attributes/! in favor of update/!. (Commit)

Notable changes

  • Bump the minimum version of the sqlite3 gem to 1.4. (Pull Request)

  • Add rails db:prepare to create a database if it doesn’t exist, and run its migrations. (Pull Request)

  • Add after_save_commit callback as shortcut for after_commit :hook, on: [ :create, :update ]. (Pull Request)

  • Add ActiveRecord::Relation#extract_associated for extracting associated records from a relation. (Pull Request)

  • Add ActiveRecord::Relation#annotate for adding SQL comments to ActiveRecord::Relation queries. (Pull Request)

  • Add support for setting Optimizer Hints on databases. (Pull Request)

  • Add insert_all/insert_all!/upsert_all methods for doing bulk inserts. (Pull Request)

  • Add rails db:seed:replant that truncates tables of each database for the current environment and loads the seeds. (Pull Request)

  • Add reselect method, which is a short-hand for unscope(:select).select(fields). (Pull Request)

  • Add negative scopes for all enum values. (Pull Request)

  • Add #destroy_by and #delete_by for conditional removals. (Pull Request)

  • Add the ability to automatically switch database connections. (Pull Request)

  • Add the ability to prevent writes to a database for the duration of a block. (Pull Request)

  • Add an API for switching connections to support multiple databases. (Pull Request)

  • Make timestamps with precision the default for migrations. (Pull Request)

  • Support :size option to change text and blob size in MySQL. (Pull Request)

  • Set both the foreign key and the foreign type columns to NULL for polymorphic associations on dependent: :nullify strategy. (Pull Request)

  • Allow a permitted instance of ActionController::Parameters to be passed as an argument to ActiveRecord::Relation#exists?. (Pull Request)

  • Add support in #where for endless ranges introduced in Ruby 2.6. (Pull Request)

  • Make ROW_FORMAT=DYNAMIC a default create table option for MySQL. (Pull Request)

  • Add the ability to disable scopes generated by ActiveRecord.enum. (Pull Request)

  • Make implicit ordering configurable for a column. (Pull Request)

  • Bump the minimum PostgreSQL version to 9.3, dropping support for 9.1 and 9.2. (Pull Request)

  • Make the values of an enum frozen, raising an error when attempting to modify them. (Pull Request)

  • Make the SQL of ActiveRecord::StatementInvalid errors its own error property and include SQL binds as a separate error property. (Pull Request)

  • Add an :if_not_exists option to create_table. (Pull Request)

  • Add support for multiple databases to rails db:schema:cache:dump and rails db:schema:cache:clear. (Pull Request)

  • Add support for hash and url configs in database hash of ActiveRecord::Base.connected_to. (Pull Request)

  • Add support for default expressions and expression indexes for MySQL. (Pull Request)

  • Add an index option for change_table migration helpers. (Pull Request)

  • Fix transaction reverting for migrations. Previously, commands inside of a transaction in a reverted migration ran uninverted. This change fixes that. (Pull Request)

  • Allow ActiveRecord::Base.configurations= to be set with a symbolized hash. (Pull Request)

  • Fix the counter cache to only update if the record is actually saved. (Pull Request)

  • Add expression indexes support for the SQLite adapter. (Pull Request)

  • Allow subclasses to redefine autosave callbacks for associated records. (Pull Request)

  • Bump the minimum MySQL version to 5.5.8. (Pull Request)

  • Use the utf8mb4 character set by default in MySQL. (Pull Request)

  • Add the ability to filter out sensitive data in #inspect (Pull Request, Pull Request)

  • Change ActiveRecord::Base.configurations to return an object instead of a hash. (Pull Request)

  • Add database configuration to disable advisory locks. (Pull Request)

  • Update SQLite3 adapter alter_table method to restore foreign keys. (Pull Request)

  • Allow the :to_table option of remove_foreign_key to be invertible. (Pull Request)

  • Fix default value for MySQL time types with specified precision. (Pull Request)

  • Fix the touch option to behave consistently with Persistence#touch method. (Pull Request)

  • Raise an exception for duplicate column definitions in Migrations. (Pull Request)

  • Bump the minimum SQLite version to 3.8. (Pull Request)

  • Fix parent records to not get saved with duplicate children records. (Pull Request)

  • Ensure Associations::CollectionAssociation#size and Associations::CollectionAssociation#empty? use loaded association ids if present. (Pull Request)

  • Add support to preload associations of polymorphic associations when not all the records have the requested associations. (Commit)

  • Add touch_all method to ActiveRecord::Relation. (Pull Request)

  • Add ActiveRecord::Base.base_class? predicate. (Pull Request)

  • Add custom prefix/suffix options to ActiveRecord::Store.store_accessor. (Pull Request)

  • Add ActiveRecord::Base.create_or_find_by/! to deal with the SELECT/INSERT race condition in ActiveRecord::Base.find_or_create_by/! by leaning on unique constraints in the database. (Pull Request)

  • Add Relation#pick as short-hand for single-value plucks. (Pull Request)

Active Storage

Please refer to the Changelog for detailed changes.



  • Deprecate config.active_storage.queue in favor of config.active_storage.queues.analysis and config.active_storage.queues.purge. (Pull Request)

  • Deprecate ActiveStorage::Downloading in favor of ActiveStorage::Blob#open. (Commit)

  • Deprecate using mini_magick directly for generating image variants in favor of image_processing. (Commit)

  • Deprecate :combine_options in Active Storage’s ImageProcessing transformer without replacement. (Commit)

Notable changes

  • Add support for generating BMP image variants. (Pull Request)

  • Add support for generating TIFF image variants. (Pull Request)

  • Add support for generating progressive JPEG image variants. (Pull Request)

  • Add ActiveStorage.routes_prefix for configuring the Active Storage generated routes. (Pull Request)

  • Generate a 404 Not Found response on ActiveStorage::DiskController#show when the requested file is missing from the disk service. (Pull Request)

  • Raise ActiveStorage::FileNotFoundError when the requested file is missing for ActiveStorage::Blob#download and ActiveStorage::Blob#open. (Pull Request)

  • Add a generic ActiveStorage::Error class that Active Storage exceptions inherit from. (Commit)

  • Persist uploaded files assigned to a record to storage when the record is saved instead of immediately. (Pull Request)

  • Optionally replace existing files instead of adding to them when assigning to a collection of attachments (as in @user.update!(images: [ … ])). Use config.active_storage.replace_on_assign_to_many to control this behavior. (Pull Request, Pull Request)

  • Add the ability to reflect on defined attachments using the existing Active Record reflection mechanism. (Pull Request)

  • Add ActiveStorage::Blob#open, which downloads a blob to a tempfile on disk and yields the tempfile. (Commit)

  • Support streaming downloads from Google Cloud Storage. Require version 1.11+ of the google-cloud-storage gem. (Pull Request)

  • Use the image_processing gem for Active Storage variants. This replaces using mini_magick directly. (Pull Request)

Active Model

Please refer to the Changelog for detailed changes.



Notable changes

  • Add a configuration option to customize format of the ActiveModel::Errors#full_message. (Pull Request)

  • Add support for configuring attribute name for has_secure_password. (Pull Request)

  • Add #slice! method to ActiveModel::Errors. (Pull Request)

  • Add ActiveModel::Errors#of_kind? to check presence of a specific error. (Pull Request)

  • Fix ActiveModel::Serializers::JSON#as_json method for timestamps. (Pull Request)

  • Fix numericality validator to still use value before type cast except Active Record. (Pull Request)

  • Fix numericality equality validation of BigDecimal and Float by casting to BigDecimal on both ends of the validation. (Pull Request)

  • Fix year value when casting a multiparameter time hash. (Pull Request)

  • Type cast falsy boolean symbols on boolean attribute as false. (Pull Request)

  • Return correct date while converting parameters in value_from_multiparameter_assignment for ActiveModel::Type::Date. (Pull Request)

  • Fall back to parent locale before falling back to the :errors namespace while fetching error translations. (Pull Request)

Active Support

Please refer to the Changelog for detailed changes.


  • Remove deprecated #acronym_regex method from Inflections. (Commit)

  • Remove deprecated Module#reachable? method. (Commit)

  • Remove Kernel#` without any replacement. (Pull Request)


  • Deprecate using negative integer arguments for String#first and String#last. (Pull Request)

  • Deprecate ActiveSupport::Multibyte::Unicode#downcase/upcase/swapcase in favor of String#downcase/upcase/swapcase. (Pull Request)

  • Deprecate ActiveSupport::Multibyte::Unicode#normalize and ActiveSupport::Multibyte::Chars#normalize in favor of String#unicode_normalize. (Pull Request)

  • Deprecate ActiveSupport::Multibyte::Chars.consumes? in favor of String#is_utf8?. (Pull Request)

  • Deprecate ActiveSupport::Multibyte::Unicode#pack_graphemes(array) and ActiveSupport::Multibyte::Unicode#unpack_graphemes(string) in favor of array.flatten.pack("U*") and string.scan(/\X/).map(&:codepoints), respectively. (Pull Request)

Notable changes

  • Add support for parallel testing. (Pull Request)

  • Make sure that String#strip_heredoc preserves frozen-ness of strings. (Pull Request)

  • Add String#truncate_bytes to truncate a string to a maximum bytesize without breaking multibyte characters or grapheme clusters. (Pull Request)

  • Add private option to delegate method in order to delegate to private methods. This option accepts true/false as the value. (Pull Request)

  • Add support for translations through I18n for ActiveSupport::Inflector#ordinal and ActiveSupport::Inflector#ordinalize. (Pull Request)

  • Add before? and after? methods to Date, DateTime, Time, and TimeWithZone. (Pull Request)

  • Fix bug where URI.unescape would fail with mixed Unicode/escaped character input. (Pull Request)

  • Fix bug where ActiveSupport::Cache would massively inflate the storage size when compression was enabled. (Pull Request)

  • Redis cache store: delete_matched no longer blocks the Redis server. (Pull Request)

  • Fix bug where ActiveSupport::TimeZone.all would fail when tzinfo data for any timezone defined in ActiveSupport::TimeZone::MAPPING was missing. (Pull Request)

  • Add Enumerable#index_with which allows creating a hash from an enumerable with the value from a passed block or a default argument. (Pull Request)

  • Allow Range#=== and Range#cover? methods to work with Range argument. (Pull Request)

  • Support key expiry in increment/decrement operations of RedisCacheStore. (Pull Request)

  • Add cpu time, idle time, and allocations features to log subscriber events. (Pull Request)

  • Add support for event object to the Active Support notification system. (Pull Request)

  • Add support for not caching nil entries by introducing new option skip_nil for ActiveSupport::Cache#fetch. (Pull Request)

  • Add Array#extract! method which removes and returns the elements for which block returns a true value. (Pull Request)

  • Keep an HTML-safe string HTML-safe after slicing. (Pull Request)

  • Add support for tracing constant autoloads via logging. (Commit)

  • Define unfreeze_time as an alias of travel_back. (Pull Request)

  • Change to return a new logger instance instead of mutating the one received as argument. (Pull Request)

  • Treat #delete_prefix, #delete_suffix and #unicode_normalize methods as non HTML-safe methods. (Pull Request)

  • Fix bug where #without for ActiveSupport::HashWithIndifferentAccess would fail with symbol arguments. (Pull Request)

  • Rename Module#parent, Module#parents, and Module#parent_name to module_parent, module_parents, and module_parent_name. (Pull Request)

  • Add ActiveSupport::ParameterFilter. (Pull Request)

  • Fix issue where duration was being rounded to a full second when a float was added to the duration. (Pull Request)

  • Make #to_options an alias for #symbolize_keys in ActiveSupport::HashWithIndifferentAccess. (Pull Request)

  • Don’t raise an exception anymore if the same block is included multiple times for a Concern. (Pull Request)

  • Preserve key order passed to ActiveSupport::CacheStore#fetch_multi. (Pull Request)

  • Fix String#safe_constantize to not throw a LoadError for incorrectly cased constant references. (Pull Request)

  • Add Hash#deep_transform_values and Hash#deep_transform_values!. (Commit)

  • Add ActiveSupport::HashWithIndifferentAccess#assoc. (Pull Request)

  • Add before_reset callback to CurrentAttributes and define after_reset as an alias of resets for symmetry. (Pull Request)

  • Revise ActiveSupport::Notifications.unsubscribe to correctly handle Regex or other multiple-pattern subscribers. (Pull Request)

  • Add new autoloading mechanism using Zeitwerk. (Commit)

  • Add Array#including and Enumerable#including to conveniently enlarge a collection. (Commit)

  • Rename Array#without and Enumerable#without to Array#excluding and Enumerable#excluding. Old method names are retained as aliases. (Commit)

  • Add support for supplying locale to transliterate and parameterize. (Pull Request)

  • Fix Time#advance to work with dates before 1001-03-07. (Pull Request)

  • Update ActiveSupport::Notifications::Instrumenter#instrument to allow not passing block. (Pull Request)

  • Use weak references in descendants tracker to allow anonymous subclasses to be garbage collected. (Pull Request)

  • Calling test methods with with_info_handler method to allow minitest-hooks plugin to work. (Commit)

  • Preserve html_safe? status on ActiveSupport::SafeBuffer#*. (Pull Request)

Active Job

Please refer to the Changelog for detailed changes.



Notable changes

  • Add support for custom serializers for Active Job arguments. (Pull Request)

  • Add support for executing Active Jobs in the timezone in which they were enqueued. (Pull Request)

  • Allow passing multiple exceptions to retry_on/discard_on. (Commit)

  • Allow calling assert_enqueued_with and assert_enqueued_email_with without a block. (Pull Request)

  • Wrap the notifications for enqueue and enqueue_at in the around_enqueue callback instead of after_enqueue callback. (Pull Request)

  • Allow calling perform_enqueued_jobs without a block. (Pull Request)

  • Allow calling assert_performed_with without a block. (Pull Request)

  • Add :queue option to job assertions and helpers. (Pull Request)

  • Add hooks to Active Job around retries and discards. (Pull Request)

  • Add a way to test for subset of arguments when performing jobs. (Pull Request)

  • Include deserialized arguments in jobs returned by Active Job test helpers. (Pull Request)

  • Allow Active Job assertion helpers to accept Proc for only keyword. (Pull Request)

  • Drop microseconds and nanoseconds from the job arguments in assertion helpers. (Pull Request)

Ruby on Rails Guides

Please refer to the Changelog for detailed changes.

Notable changes

  • Add Multiple Databases with Active Record guide. (Pull Request)

  • Add a section about troubleshooting of autoloading constants. (Commit)

  • Add Action Mailbox Basics guide. (Pull Request)

  • Add Action Text Overview guide. (Pull Request)


See the full list of contributors to Rails for the many people who spent many hours making Rails, the stable and robust framework it is. Kudos to all of them.