1. Upgrading to Rails 6.0

If you're upgrading an existing application, it's a great idea to have good testcoverage before going in. You should also first upgrade to Rails 5.2 in case youhaven't and make sure your application still runs as expected before attemptingan update to Rails 6.0. A list of things to watch out for when upgrading isavailable in theUpgrading Ruby on Railsguide.

2. Major Features

2.1. Action Mailbox

Pull Request

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

2.2. Action Text

Pull Request

Action Textbrings rich text content and editing to Rails. It includestheTrix editor that handles everything from formattingto links to quotes to lists to embedded images and galleries.The rich text content generated by the Trix editor is saved in its ownRichText model that's associated with any existing Active Record model in the application.Any embedded images (or other attachments) are automatically stored usingActive Storage and associated with the included RichText model.

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

2.3. Parallel Testing

Pull Request

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

2.4. Action Cable Testing

Pull Request

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

3. Railties

Please refer to theChangelog for detailed changes.

3.1. Removals

• Remove deprecatedafter_bundle helper inside plugins templates.(Commit)

• Remove deprecated support toconfig.ru that uses the applicationclass as argument ofrun.(Commit)

• Remove deprecatedenvironment argument from the rails commands.(Commit)

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

• Remove deprecatedconfig.secret_token.(Commit)

3.2. Deprecations

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

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

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

3.3. Notable changes

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

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

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

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

• Addrails 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 forrails db:migrate:status command.(Pull Request)

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

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

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

4. Action Cable

Please refer to theChangelog for detailed changes.

4.1. Removals

• ReplaceActionCable.startDebugging() andActionCable.stopDebugging()withActionCable.logger.enabled.(Pull Request)

4.2. Deprecations

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

4.3. Notable changes

• Add support for thechannel_prefix option for PostgreSQL subscription adaptersincable.yml.(Pull Request)

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

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

• AddChannel::Base#broadcast_to andChannel::Base.broadcasting_for.(Pull Request)

• Close a connection when callingreject_unauthorized_connection from anActionCable::Connection.(Pull Request)

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

• Move the configuration of the WebSocket adapter and logger adapterfrom properties ofActionCable toActionCable.adapters.(Pull Request)

• Add anid option to the Redis adapter to distinguish Action Cable's Redisconnections.(Pull Request)

5. Action Pack

Please refer to theChangelog for detailed changes.

5.1. Removals

• Remove deprecatedfragment_cache_key helper in favor ofcombined_fragment_cache_key.(Commit)

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

5.2. Deprecations

• DeprecateActionDispatch::Http::ParameterFilter in favor ofActiveSupport::ParameterFilter.(Pull Request)

• Deprecate controller levelforce_ssl in favor ofconfig.force_ssl.(Pull Request)

5.3. Notable changes

• ChangeActionDispatch::Response#content_type returning Content-Typeheader as it is.(Pull Request)

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

• AllowActionDispatch::SystemTestCase.driven_by to be called with a blockto define specific browser capabilities.(Pull Request)

• AddActionDispatch::HostAuthorization middleware that guards against DNS rebindingattacks.(Pull Request)

• Allow the use ofparsed_body inActionController::TestCase.(Pull Request)

• Raise anArgumentError when multiple root routes exist in the same contextwithoutas: naming specifications.(Pull Request)

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

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

• Encode Content-Disposition filenames onsend_data andsend_file.(Pull Request)

• ExposeActionController::Parameters#each_key.(Pull Request)

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

• RaiseActionController::RespondToMismatchError for conflictingrespond_to invocations.(Pull Request)

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

• IntroduceActionDispatch::DebugExceptions.register_interceptor, a way to hook intoDebugExceptions 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 configurationthat can be explicitly included in controllers.(Pull Request)

• Add#dig toActionDispatch::Request::Session.(Pull Request)

6. Action View

Please refer to theChangelog for detailed changes.

6.1. Removals

• Remove deprecatedimage_alt helper.(Commit)

• Remove an emptyRecordTagHelper module from which the functionalitywas already moved to therecord_tag_helper gem.(Commit)

6.2. Deprecations

• DeprecateActionView::Template.finalize_compiled_template_methods withno replacement.(Pull Request)

• Deprecateconfig.action_view.finalize_compiled_template_methods withno replacement.(Pull Request)

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

6.3. Notable changes

• Clear Action View cache in development only on file changes, speeding updevelopment 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 ayear_format option todate_select tag, making it possible tocustomize year names.(Pull Request)

• Add anonce: true option forjavascript_include_tag helper tosupport automatic nonce generation for a Content Security Policy.(Pull Request)

• Add aaction_view.finalize_compiled_template_methods configuration to disable orenableActionView::Template finalizers.(Pull Request)

• Extract the JavaScriptconfirm call to its own, overridable method inrails_ujs.(Pull Request)

• Add aaction_controller.default_enforce_utf8 configuration option to handleenforcing UTF-8 encoding. This defaults tofalse.(Pull Request)

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

7. Action Mailer

Please refer to theChangelog for detailed changes.

7.1. Removals

7.2. Deprecations

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

• DeprecateDeliveryJob andParameterized::DeliveryJob in favor ofMailDeliveryJob.(Pull Request)

7.3. Notable changes

• AddMailDeliveryJob 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 ofusing just the action name.(Pull Request)

• Addperform_deliveries to payload ofdeliver.action_mailer notification.(Pull Request)

• Improve the logging message whenperform_deliveries is false to indicatethat sending of emails was skipped.(Pull Request)

• Allow callingassert_enqueued_email_with without block.(Pull Request)

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

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

8. Active Record

Please refer to theChangelog for detailed changes.

8.1. Removals

• 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 deprecatedActiveRecord::ConnectionAdapters::SQLite3Adapter#valid_alter_table_type?.(Commit)

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

• Remove support for passing the column name tocount 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 deprecatedActiveRecord::Migrator.migrations_path=.(Commit)

• Remove deprecatedexpand_hash_conditions_for_aggregates.(Commit)

8.2. Deprecations

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

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

• Deprecateconfig.active_record.sqlite3.represent_boolean_as_integer.(Commit)

• Deprecate passingmigrations_paths toconnection.assume_migrated_upto_version.(Commit)

• DeprecateActiveRecord::Result#to_hash in favor ofActiveRecord::Result#to_a.(Commit)

• Deprecate methods inDatabaseLimits:column_name_length,table_name_length,columns_per_table,indexes_per_table,columns_per_multicolumn_index,sql_query_length, andjoins_per_query.(Commit)

• Deprecateupdate_attributes/! in favor ofupdate/!.(Commit)

8.3. Notable changes

• Bump the minimum version of thesqlite3 gem to 1.4.(Pull Request)

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

• Addafter_save_commit callback as shortcut forafter_commit :hook, on: [ :create, :update ].(Pull Request)

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

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

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

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

• Addrails db:seed:replant that truncates tables of each databasefor the current environment and loads the seeds.(Pull Request)

• Addreselect method, which is a short-hand forunscope(: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 forpolymorphic associations ondependent: :nullify strategy.(Pull Request)

• Allow a permitted instance ofActionController::Parameters to be passed as anargument toActiveRecord::Relation#exists?.(Pull Request)

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

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

• Add the ability to disable scopes generated byActiveRecord.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 ofActiveRecord::StatementInvalid errors its own error propertyand include SQL binds as a separate error property.(Pull Request)

• Add an:if_not_exists option tocreate_table.(Pull Request)

• Add support for multiple databases torails db:schema:cache:dumpandrails db:schema:cache:clear.(Pull Request)

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

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

• Add anindex option forchange_table migration helpers.(Pull Request)

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

• AllowActiveRecord::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)

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

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

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

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

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

• Fix thetouch option to behave consistently withPersistence#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)

• EnsureAssociations::CollectionAssociation#size andAssociations::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)

• Addtouch_all method toActiveRecord::Relation.(Pull Request)

• AddActiveRecord::Base.base_class? predicate.(Pull Request)

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

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

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

9. Active Storage

Please refer to theChangelog for detailed changes.

9.1. Removals

9.2. Deprecations

• Deprecateconfig.active_storage.queue in favor ofconfig.active_storage.queues.analysisandconfig.active_storage.queues.purge.(Pull Request)

• DeprecateActiveStorage::Downloading in favor ofActiveStorage::Blob#open.(Commit)

• Deprecate usingmini_magick directly for generating image variants in favor ofimage_processing.(Commit)

• Deprecate:combine_options in Active Storage's ImageProcessing transformerwithout replacement.(Commit)

9.3. 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)

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

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

• RaiseActiveStorage::FileNotFoundError when the requested file is missing forActiveStorage::Blob#download andActiveStorage::Blob#open.(Pull Request)

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

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

• Optionally replace existing files instead of adding to them when assigning toa collection of attachments (as in@user.update!(images: [ … ])). Useconfig.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 existingActive Record reflection mechanism.(Pull Request)

• AddActiveStorage::Blob#open, which downloads a blob to a tempfile on diskand yields the tempfile.(Commit)

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

• Use theimage_processing gem for Active Storage variants. This replaces usingmini_magick directly.(Pull Request)

10. Active Model

Please refer to theChangelog for detailed changes.

10.1. Removals

10.2. Deprecations

10.3. Notable changes

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

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

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

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

• FixActiveModel::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 ofBigDecimal andFloatby casting toBigDecimal 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 invalue_from_multiparameter_assignmentforActiveModel::Type::Date.(Pull Request)

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

11. Active Support

Please refer to theChangelog for detailed changes.

11.1. Removals

• Remove deprecated#acronym_regex method fromInflections.(Commit)

• Remove deprecatedModule#reachable? method.(Commit)

• RemoveKernel#` without any replacement.(Pull Request)

11.2. Deprecations

• Deprecate using negative integer arguments forString#first andString#last.(Pull Request)

• DeprecateActiveSupport::Multibyte::Unicode#downcase/upcase/swapcasein favor ofString#downcase/upcase/swapcase.(Pull Request)

• DeprecateActiveSupport::Multibyte::Unicode#normalizeandActiveSupport::Multibyte::Chars#normalize in favor ofString#unicode_normalize.(Pull Request)

• DeprecateActiveSupport::Multibyte::Chars.consumes? in favor ofString#is_utf8?.(Pull Request)

• DeprecateActiveSupport::Multibyte::Unicode#pack_graphemes(array)andActiveSupport::Multibyte::Unicode#unpack_graphemes(string)in favor ofarray.flatten.pack("U*") andstring.scan(/\X/).map(&:codepoints),respectively.(Pull Request)

11.3. Notable changes

• Add support for parallel testing.(Pull Request)

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

• AddString#truncate_bytes to truncate a string to a maximum bytesizewithout breaking multibyte characters or grapheme clusters.(Pull Request)

• Addprivate option todelegate method in order to delegate toprivate methods. This option acceptstrue/false as the value.(Pull Request)

• Add support for translations through I18n forActiveSupport::Inflector#ordinalandActiveSupport::Inflector#ordinalize.(Pull Request)

• Addbefore? andafter? methods toDate,DateTime,Time, andTimeWithZone.(Pull Request)

• Fix bug whereURI.unescape would fail with mixed Unicode/escaped characterinput.(Pull Request)

• Fix bug whereActiveSupport::Cache would massively inflate the storagesize when compression was enabled.(Pull Request)

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

• Fix bug whereActiveSupport::TimeZone.all would fail when tzinfo data forany timezone defined inActiveSupport::TimeZone::MAPPING was missing.(Pull Request)

• AddEnumerable#index_with which allows creating a hash from an enumerablewith the value from a passed block or a default argument.(Pull Request)

• AllowRange#=== andRange#cover? methods to work withRange argument.(Pull Request)

• Support key expiry inincrement/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 cachingnil entries by introducing new optionskip_nilforActiveSupport::Cache#fetch.(Pull Request)

• AddArray#extract! method which removes and returns the elements for whichblock 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)

• Defineunfreeze_time as an alias oftravel_back.(Pull Request)

• ChangeActiveSupport::TaggedLogging.new to return a new logger instanceinstead of mutating the one received as argument.(Pull Request)

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

• Fix bug where#without forActiveSupport::HashWithIndifferentAccesswould fail with symbol arguments.(Pull Request)

• RenameModule#parent,Module#parents, andModule#parent_name tomodule_parent,module_parents, andmodule_parent_name.(Pull Request)

• AddActiveSupport::ParameterFilter.(Pull Request)

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

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

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

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

• FixString#safe_constantize to not throw aLoadError for incorrectlycased constant references.(Pull Request)

• AddHash#deep_transform_values andHash#deep_transform_values!.(Commit)

• AddActiveSupport::HashWithIndifferentAccess#assoc.(Pull Request)

• Addbefore_reset callback toCurrentAttributes and defineafter_reset as an alias ofresets for symmetry.(Pull Request)

• ReviseActiveSupport::Notifications.unsubscribe to correctlyhandle Regex or other multiple-pattern subscribers.(Pull Request)

• Add new autoloading mechanism using Zeitwerk.(Commit)

• AddArray#including andEnumerable#including to conveniently enlargea collection.(Commit)

• RenameArray#without andEnumerable#without toArray#excludingandEnumerable#excluding. Old method names are retained as aliases.(Commit)

• Add support for supplyinglocale totransliterate andparameterize.(Pull Request)

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

• UpdateActiveSupport::Notifications::Instrumenter#instrument to allownot passing block.(Pull Request)

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

• Calling test methods withwith_info_handler method to allow minitest-hooksplugin to work.(Commit)

• Preservehtml_safe? status onActiveSupport::SafeBuffer#*.(Pull Request)

12. Active Job

Please refer to theChangelog for detailed changes.

12.1. Removals

• Remove support for Qu gem.(Pull Request)

12.2. Deprecations

12.3. Notable changes

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

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

• Allow passing multiple exceptions toretry_on/discard_on.(Commit)

• Allow callingassert_enqueued_with andassert_enqueued_email_with without a block.(Pull Request)

• Wrap the notifications forenqueue andenqueue_at in thearound_enqueuecallback instead ofafter_enqueue callback.(Pull Request)

• Allow callingperform_enqueued_jobs without a block.(Pull Request)

• Allow callingassert_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 Jobtest helpers.(Pull Request)

• Allow Active Job assertion helpers to accept Proc foronlykeyword.(Pull Request)

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

13. Ruby on Rails Guides

Please refer to theChangelog for detailed changes.

13.1. 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)

14. Credits

See thefull list of contributors to Railsfor the many people who spent many hours making Rails, the stable and robustframework it is. Kudos to all of them.