rails--rails/activerecord/CHANGELOG.md

• Version the API presented to migration classes, so we can change parameter defaults without breaking existing migrations, or forcing them to be rewritten through a deprecation cycle.

  Matthew Draper, Ravil Bayramgalin

• Use bind params for limit and offset. This will generate significantly fewer prepared statements for common tasks like pagination. To support this change, passing a string containing a comma to limit has been deprecated, and passing an Arel node to limit is no longer supported.

  Fixes #22250

  Sean Griffin

• Introduce after_{create,update,delete}_commit callbacks.

  Before:

  after_commit :add_to_index_later, on: :create
  after_commit :update_in_index_later, on: :update
  after_commit :remove_from_index_later, on: :destroy
  

  After:

  after_create_commit  :add_to_index_later
  after_update_commit  :update_in_index_later
  after_destroy_commit :remove_from_index_later
  

  Fixes #22515.

  Genadi Samokovarov

• Respect the column default values for inheritance_column when instantiating records through the base class.

  Fixes #17121.

  Example:

  # The schema of BaseModel has `t.string :type, default: 'SubType'`
  subtype = BaseModel.new
  assert_equals SubType, subtype.class
  

  Kuldeep Aggarwal

• Fix rake db:structure:dump on Postgres when multiple schemas are used.

  Fixes #22346.

  Nick Muerdter, ckoenig

• Add schema dumping support for PostgreSQL geometric data types.

  Ryuta Kamizono

• Except keys of build_record's argument from create_scope in initialize_attributes.

  Fixes #21893.

  Yuichiro Kaneko

• Deprecate connection.tables on the SQLite3 and MySQL adapters. Also deprecate passing arguments to #tables. And deprecate table_exists?.

  The #tables method of some adapters (mysql, mysql2, sqlite3) would return both tables and views while others (postgresql) just return tables. To make their behavior consistent, #tables will return only tables in the future.

  The #table_exists? method would check both tables and views. To make their behavior consistent with #tables, #table_exists? will check only tables in the future.

  Yuichiro Kaneko

• Improve support for non Active Record objects on validates_associated

  Skipping marked_for_destruction? when the associated object does not responds to it make easier to validate virtual associations built on top of Active Model objects and/or serialized objects that implement a valid? instance method.

  Kassio Borges, Lucas Mazza

• Change connection management middleware to return a new response with a body proxy, rather than mutating the original.

  Kevin Buchanan

• Make db:migrate:status to render 1_some.rb format migrate files.

  These files are in db/migrate:

  * 1_valid_people_have_last_names.rb
  * 20150819202140_irreversible_migration.rb
  * 20150823202140_add_admin_flag_to_users.rb
  * 20150823202141_migration_tests.rb
  * 2_we_need_reminders.rb
  * 3_innocent_jointable.rb
  

  Before:

  $ bundle exec rake db:migrate:status
  ...
  
   Status   Migration ID    Migration Name
  --------------------------------------------------
     up     001             ********** NO FILE **********
     up     002             ********** NO FILE **********
     up     003             ********** NO FILE **********
     up     20150819202140  Irreversible migration
     up     20150823202140  Add admin flag to users
     up     20150823202141  Migration tests
  

  After:

  $ bundle exec rake db:migrate:status
  ...
  
   Status   Migration ID    Migration Name
  --------------------------------------------------
     up     001             Valid people have last names
     up     002             We need reminders
     up     003             Innocent jointable
     up     20150819202140  Irreversible migration
     up     20150823202140  Add admin flag to users
     up     20150823202141  Migration tests
  

  Yuichiro Kaneko

• Define ActiveRecord::Sanitization.sanitize_sql_for_order and use it inside preprocess_order_args.

  Yuichiro Kaneko

• Allow bigint with default nil for avoiding auto increment primary key.

  Ryuta Kamizono

• Remove DEFAULT_CHARSET and DEFAULT_COLLATION in MySQLDatabaseTasks.

  We should omit the collation entirely rather than providing a default. Then the choice is the responsibility of the server and MySQL distribution.

  Ryuta Kamizono

• Alias ActiveRecord::Relation#left_joins to ActiveRecord::Relation#left_outer_joins.

  Takashi Kokubun

• Use advisory locking to raise a ConcurrentMigrationError instead of attempting to migrate when another migration is currently running.

  Sam Davies

• Added ActiveRecord::Relation#left_outer_joins.

  Example:

  User.left_outer_joins(:posts)
  # => SELECT "users".* FROM "users" LEFT OUTER JOIN "posts" ON
       "posts"."user_id" = "users"."id"
  

  Florian Thomas

• Support passing an array to order for SQL parameter sanitization.

  Aaron Suggs

• Avoid disabling errors on the PostgreSQL connection when enabling the standard_conforming_strings setting. Errors were previously disabled because the setting wasn't writable in Postgres 8.1 and didn't exist in earlier versions. Now Rails only supports Postgres 8.2+ we're fine to assume the setting exists. Disabling errors caused problems when using a connection pooling tool like PgBouncer because it's not guaranteed to have the same connection between calls to execute and it could leave the connection with errors disabled.

  Fixes #22101.

  Harry Marr

• Set scope.reordering_value to true if :reordering-values are specified.

  Fixes #21886.

  Hiroaki Izu

• Add support for bidirectional destroy dependencies.

  Fixes #13609.

  Example:

  class Content < ActiveRecord::Base
    has_one :position, dependent: :destroy
  end
  
  class Position < ActiveRecord::Base
    belongs_to :content, dependent: :destroy
  end
  

  Seb Jacobs

• Includes HABTM returns correct size now. It's caused by the join dependency only instantiates one HABTM object because the join table hasn't a primary key.

  Fixes #16032.

  Examples:

  before:
  
  Project.first.salaried_developers.size # => 3
  Project.includes(:salaried_developers).first.salaried_developers.size # => 1
  
  after:
  
  Project.first.salaried_developers.size # => 3
  Project.includes(:salaried_developers).first.salaried_developers.size # => 3
  

  Bigxiang

• Add option to index errors in nested attributes

  For models which have nested attributes, errors within those models will now be indexed if :index_errors is specified when defining a has_many relationship, or if its set in the global config.

  Example:

  class Guitar < ActiveRecord::Base
    has_many :tuning_pegs
    accepts_nested_attributes_for :tuning_pegs
  end
  
  class TuningPeg < ActiveRecord::Base
    belongs_to :guitar
    validates_numericality_of :pitch
  end
  
  # Old style
  guitar.errors["tuning_pegs.pitch"] = ["is not a number"]
  
  # New style (if defined globally, or set in has_many_relationship)
  guitar.errors["tuning_pegs[1].pitch"] = ["is not a number"]
  

  Michael Probber, Terence Sun

• Exit with non-zero status for failed database rake tasks.

  Jay Hayes

• Queries such as Computer.joins(:monitor).group(:status).count will now be interpreted as Computer.joins(:monitor).group('computers.status').count so that when Computer and Monitor have both status columns we don't have conflicts in projection.

  Rafael Sales

• Add ability to default to uuid as primary key when generating database migrations.

  Example:

  config.generators do |g|
    g.orm :active_record, primary_key_type: :uuid
  end
  

  Jon McCartie

• Don't cache arguments in #find_by if they are an ActiveRecord::Relation.

  Fixes #20817

  Hiroaki Izu

• Qualify column name inserted by group in calculation.

  Giving group an unqualified column name now works, even if the relation has JOIN with another table which also has a column of the name.

  Soutaro Matsumoto

• Don't cache prepared statements containing an IN clause or a SQL literal, as these queries will change often and are unlikely to have a cache hit.

  Sean Griffin

• Fix rewhere in a has_many association.

  Fixes #21955.

  Josh Branchaud, Kal

• where raises ArgumentError on unsupported types.

  Fixes #20473.

  Jake Worth

• Add an immutable string type to help reduce memory usage for apps which do not need mutation detection on strings.

  Sean Griffin

• Give AcriveRecord::Relation#update its own deprecation warning when passed an ActiveRecord::Base instance.

  Fixes #21945.

  Ted Johansson

• Make it possible to pass :to_table when adding a foreign key through add_reference.

  Fixes #21563.

  Yves Senn

• No longer pass deprecated option -i to pg_dump.

  Paul Sadauskas

• Concurrent AR::Base#increment! and #decrement! on the same record are all reflected in the database rather than overwriting each other.

  Bogdan Gusiev

• Avoid leaking the first relation we call first on, per model.

  Fixes #21921.

  Matthew Draper, Jean Boussier

• Remove unused pk_and_sequence_for in AbstractMysqlAdapter.

  Ryuta Kamizono

• Allow fixtures files to set the model class in the YAML file itself.

  To load the fixtures file accounts.yml as the User model, use:

  _fixture:
    model_class: User
  david:
    name: David
  

  Fixes #9516.

  Roque Pinel

• Don't require a database connection to load a class which uses acceptance validations.

  Sean Griffin

• Correctly apply unscope when preloading through associations.

  Jimmy Bourassa

• Fixed taking precision into count when assigning a value to timestamp attribute.

  Timestamp column can have less precision than ruby timestamp In result in how big a fraction of a second can be stored in the database.

  m = Model.create!
  m.created_at.usec == m.reload.created_at.usec # => false
  # due to different precision in Time.now and database column
  

  If the precision is low enough, (mysql default is 0, so it is always low enough by default) the value changes when model is reloaded from the database. This patch fixes that issue ensuring that any timestamp assigned as an attribute is converted to column precision under the attribute.

  Bogdan Gusiev

• Introduce connection.data_sources and connection.data_source_exists?. These methods determine what relations can be used to back Active Record models (usually tables and views).

  Also deprecate SchemaCache#tables, SchemaCache#table_exists? and SchemaCache#clear_table_cache! in favor of their new data source counterparts.

  Yves Senn, Matthew Draper

• Add ActiveRecord::Base.ignored_columns to make some columns invisible from Active Record.

  Jean Boussier

• ActiveRecord::Tasks::MySQLDatabaseTasks fails if shellout to mysql commands (like mysqldump) is not successful.

  Steve Mitchell

• Ensure select quotes aliased attributes, even when using from.

  Fixes #21488

  Sean Griffin & @johanlunds

• MySQL: support unsigned numeric data types.

  Example:

  create_table :foos do |t|
    t.unsigned_integer :quantity
    t.unsigned_bigint  :total
    t.unsigned_float   :percentage
    t.unsigned_decimal :price, precision: 10, scale: 2
  end
  

  The unsigned: true option may be used for the primary key:

  create_table :foos, id: :bigint, unsigned: true do |t|
    …
  end
  

  Ryuta Kamizono

• Add #views and #view_exists? methods on connection adapters.

  Ryuta Kamizono

• Correctly dump composite primary key.

  Example:

  create_table :barcodes, primary_key: ["region", "code"] do |t|
    t.string :region
    t.integer :code
  end
  

  Ryuta Kamizono

• Lookup the attribute name for restrict_with_error messages on the model class that defines the association.

  kuboon, Ronak Jangir

• Correct query for PostgreSQL 8.2 compatibility.

  Ben Murphy, Matthew Draper

• bin/rake db:migrate uses ActiveRecord::Tasks::DatabaseTasks.migrations_paths instead of Migrator.migrations_paths.

  Tobias Bielohlawek

• Support dropping indexes concurrently in PostgreSQL.

  See http://www.postgresql.org/docs/9.4/static/sql-dropindex.html for more details.

  Grey Baker

• Deprecate passing conditions to ActiveRecord::Relation#delete_all and ActiveRecord::Relation#destroy_all.

  Wojciech Wnętrzak

• Instantiating an AR model with ActionController::Parameters now raises an ActiveModel::ForbiddenAttributesError if the parameters include a type field that has not been explicitly permitted. Previously, the type field was simply ignored in the same situation.

  Prem Sichanugrist

• PostgreSQL, create_schema, drop_schema and rename_table now quote schema names.

  Fixes #21418.

  Example:

  create_schema("my.schema")
  # CREATE SCHEMA "my.schema";
  

  Yves Senn

• PostgreSQL, add :if_exists option to #drop_schema. This makes it possible to drop a schema that might exist without raising an exception if it doesn't.

  Yves Senn

• Only try to nullify has_one target association if the record is persisted.

  Fixes #21223.

  Agis Anastasopoulos

• Uniqueness validator raises descriptive error when running on a persisted record without primary key.

  Fixes #21304.

  Yves Senn

• Add a native JSON data type support in MySQL.

  Example:

  create_table :json_data_type do |t|
    t.json :settings
  end
  

  Ryuta Kamizono

• Descriptive error message when fixtures contain a missing column.

  Fixes #21201.

  Yves Senn

• ActiveRecord::Tasks::PostgreSQLDatabaseTasks fail if shellout to postgresql commands (like pg_dump) is not successful.

  Bryan Paxton, Nate Berkopec

• Add ActiveRecord::Relation#in_batches to work with records and relations in batches.

  Available options are of (batch size), load, begin_at, and end_at.

  Examples:

  Person.in_batches.each_record(&:party_all_night!)
  Person.in_batches.update_all(awesome: true)
  Person.in_batches.delete_all
  Person.in_batches.each do |relation|
    relation.delete_all
    sleep 10 # Throttles the delete queries
  end
  

  Fixes #20933.

  Sina Siadat

• Added methods for PostgreSQL geometric data types to use in migrations.

  Example:

  create_table :foo do |t|
    t.line :foo_line
    t.lseg :foo_lseg
    t.box :foo_box
    t.path :foo_path
    t.polygon :foo_polygon
    t.circle :foo_circle
  end
  

  Mehmet Emin İNAÇ

• Add cache_key to ActiveRecord::Relation.

  Example:

  @users = User.where("name like ?", "%Alberto%")
  @users.cache_key
  # => "/users/query-5942b155a43b139f2471b872ac54251f-3-20150714212107656125000"
  

  Alberto Fernández-Capel

• Properly allow uniqueness validations on primary keys.

  Fixes #20966.

  Sean Griffin, presskey

• Don't raise an error if an association failed to destroy when destroy was called on the parent (as opposed to destroy!).

  Fixes #20991.

  Sean Griffin

• ActiveRecord::RecordNotFound modified to store model name, primary_key and id of the caller model. It allows the catcher of this exception to make a better decision to what to do with it.

  Example:

  class SomeAbstractController < ActionController::Base
    rescue_from ActiveRecord::RecordNotFound, with: :redirect_to_404
  
    private def redirect_to_404(e)
      return redirect_to(posts_url) if e.model == 'Post'
      raise
    end
  end
  

  Sameer Rahmani

• Deprecate the keys for association restrict_dependent_destroy errors in favor of new key names.

  Previously has_one and has_many associations were using the one and many keys respectively. Both of these keys have special meaning in I18n (they are considered to be pluralizations) so by renaming them to has_one and has_many we make the messages more explicit and most importantly they don't clash with linguistical systems that need to validate translation keys (and their pluralizations).

  The :'restrict_dependent_destroy.one' key should be replaced with :'restrict_dependent_destroy.has_one', and :'restrict_dependent_destroy.many' with :'restrict_dependent_destroy.has_many'.

  Roque Pinel, Christopher Dell

• Fix state being carried over from previous transaction.

  Considering the following example where name is a required attribute. Before we had new_record? returning true for a persisted record:

  author = Author.create! name: 'foo'
  author.name = nil
  author.save        # => false
  author.new_record? # => true
  

  Fixes #20824.

  Roque Pinel

• Correctly ignore mark_for_destruction when autosave isn't set to true when validating associations.

  Fixes #20882.

  Sean Griffin

• Fix a bug where counter_cache doesn't always work with polymorphic relations.

  Fixes #16407.

  Stefan Kanev, Sean Griffin

• Ensure that cyclic associations with autosave don't cause duplicate errors to be added to the parent record.

  Fixes #20874.

  Sean Griffin

• Ensure that ActionController::Parameters can still be passed to nested attributes.

  Fixes #20922.

  Sean Griffin

• Deprecate force association reload by passing a truthy argument to association method.

  For collection association, you can call #reload on association proxy to force a reload:

  @user.posts.reload   # Instead of @user.posts(true)
  

  For singular association, you can call #reload on the parent object to clear its association cache then call the association method:

  @user.reload.profile   # Instead of @user.profile(true)
  

  Passing a truthy argument to force association to reload will be removed in Rails 5.1.

  Prem Sichanugrist

• Replaced ActiveSupport::Concurrency::Latch with Concurrent::CountDownLatch from the concurrent-ruby gem.

  Jerry D'Antonio

• Fix through associations using scopes having the scope merged multiple times.

  Fixes #20721. Fixes #20727.

  Sean Griffin

• ActiveRecord::Base.dump_schema_after_migration applies migration tasks other than db:migrate. (eg. db:rollback, db:migrate:dup, ...)

  Fixes #20743.

  Yves Senn

• Add alternate syntax to make change_column_default reversible.

  User can pass in :from and :to to make change_column_default command become reversible.

  Example:

  change_column_default :posts, :status, from: nil, to: "draft"
  change_column_default :users, :authorized, from: true, to: false
  

  Prem Sichanugrist

• Prevent error when using force_reload: true on an unassigned polymorphic belongs_to association.

  Fixes #20426.

  James Dabbs

• Correctly raise ActiveRecord::AssociationTypeMismatch when assigning a wrong type to a namespaced association.

  Fixes #20545.

  Diego Carrion

• validates_absence_of respects marked_for_destruction?.

  Fixes #20449.

  Yves Senn

• Include the Enumerable module in ActiveRecord::Relation

  Sean Griffin & bogdan

• Use Enumerable#sum in ActiveRecord::Relation if a block is given.

  Sean Griffin

• Let WITH queries (Common Table Expressions) be explainable.

  Vladimir Kochnev

• Make remove_index :table, :column reversible.

  Yves Senn

• Fixed an error which would occur in dirty checking when calling update_attributes from a getter.

  Fixes #20531.

  Sean Griffin

• Make remove_foreign_key reversible. Any foreign key options must be specified, similar to remove_column.

  Aster Ryan

• Add :_prefix and :_suffix options to enum definition.

  Fixes #17511, #17415.

  Igor Kapkov

• Correctly handle decimal arrays with defaults in the schema dumper.

  Fixes #20515.

  Sean Griffin & jmondo

• Deprecate the PostgreSQL :point type in favor of a new one which will return Point objects instead of an Array

  Sean Griffin

• Ensure symbols passed to ActiveRecord::Relation#select are always treated as columns.

  Fixes #20360.

  Sean Griffin

• Do not set sql_mode if strict: :default is specified.

  # config/database.yml
  production:
    adapter: mysql2
    database: foo_prod
    user: foo
    strict: :default
  

  Ryuta Kamizono

• Allow proc defaults to be passed to the attributes API. See documentation for examples.

  Sean Griffin, Kir Shatrov

• SQLite: :collation support for string and text columns.

  Example:

  create_table :foo do |t|
    t.string :string_nocase, collation: 'NOCASE'
    t.text :text_rtrim, collation: 'RTRIM'
  end
  
  add_column :foo, :title, :string, collation: 'RTRIM'
  
  change_column :foo, :title, :string, collation: 'NOCASE'
  

  Akshay Vishnoi

• Allow the use of symbols or strings to specify enum values in test fixtures:

  awdr:
    title: "Agile Web Development with Rails"
    status: :proposed
  

  George Claghorn

• Clear query cache when ActiveRecord::Base#reload is called.

  Shane Hender, Pierre Nespo

• Include stored procedures and function on the MySQL structure dump.

  Jonathan Worek

• Pass :extend option for has_and_belongs_to_many associations to the underlying has_many :through.

  Jaehyun Shin

• Deprecate Relation#uniq use Relation#distinct instead.

  See #9683.

  Yves Senn

• Allow single table inheritance instantiation to work when storing demodulized class names.

  Alex Robbin

• Correctly pass MySQL options when using structure_dump or structure_load.

  Specifically, it fixes an issue when using SSL authentication.

  Alex Coomans

• Dump indexes in create_table instead of add_index.

  If the adapter supports indexes in create_table, generated SQL is slightly more efficient.

  Ryuta Kamizono

• Correctly dump :options on create_table for MySQL.

  Ryuta Kamizono

• PostgreSQL: :collation support for string and text columns.

  Example:

  create_table :foos do |t|
    t.string :string_en, collation: 'en_US.UTF-8'
    t.text   :text_ja,   collation: 'ja_JP.UTF-8'
  end
  

  Ryuta Kamizono

• Remove ActiveRecord::Serialization::XmlSerializer from core.

  Zachary Scott

• Make unscope aware of "less than" and "greater than" conditions.

  TAKAHASHI Kazuaki

• find_by and find_by! raise ArgumentError when called without arguments.

  Kohei Suzuki

• Revert behavior of db:schema:load back to loading the full environment. This ensures that initializers are run.

  Fixes #19545.

  Yves Senn

• Fix missing index when using timestamps with the index option.

  The index option used with timestamps should be passed to both column definitions for created_at and updated_at rather than just the first.

  Paul Mucur

• Rename :class to :anonymous_class in association options.

  Fixes #19659.

  Andrew White

• Autosave existing records on a has many through association when the parent is new.

  Fixes #19782.

  Sean Griffin

• Fixed a bug where uniqueness validations would error on out of range values, even if an validation should have prevented it from hitting the database.

  Andrey Voronkov

• MySQL: :charset and :collation support for string and text columns.

  Example:

  create_table :foos do |t|
    t.string :string_utf8_bin, charset: 'utf8', collation: 'utf8_bin'
    t.text   :text_ascii,      charset: 'ascii'
  end
  

  Ryuta Kamizono

• Foreign key related methods in the migration DSL respect ActiveRecord::Base.pluralize_table_names = false.

  Fixes #19643.

  Mehmet Emin İNAÇ

• Reduce memory usage from loading types on PostgreSQL.

  Fixes #19578.

  Sean Griffin

• Add config.active_record.warn_on_records_fetched_greater_than option.

  When set to an integer, a warning will be logged whenever a result set larger than the specified size is returned by a query.

  Fixes #16463.

  Jason Nochlin

• Ignore .psqlrc when loading database structure.

  Jason Weathered

• Fix referencing wrong table aliases while joining tables of has many through association (only when calling calculation methods).

  Fixes #19276.

  pinglamb

• Correctly persist a serialized attribute that has been returned to its default value by an in-place modification.

  Fixes #19467.

  Matthew Draper

• Fix generating the schema file when using PostgreSQL BigInt[] data type. Previously the limit: 8 was not coming through, and this caused it to become Int[] data type after rebuilding from the schema.

  Fixes #19420.

  Jake Waller

• Reuse the CollectionAssociation#reader cache when the foreign key is available prior to save.

  Ben Woosley

• Add config.active_record.dump_schemas to fix db:structure:dump when using schema_search_path and PostgreSQL extensions.

  Fixes #17157.

  Ryan Wallace

• Renaming use_transactional_fixtures to use_transactional_tests for clarity.

  Fixes #18864.

  Brandon Weiss

• Increase pg gem version requirement to ~> 0.18. Earlier versions of the pg gem are known to have problems with Ruby 2.2.

  Matt Brictson

• Correctly dump serial and bigserial.

  Ryuta Kamizono

• Fix default format value in ActiveRecord::Tasks::DatabaseTasks#schema_file.

  James Cox

• Don't enroll records in the transaction if they don't have commit callbacks. This was causing a memory leak when creating many records inside a transaction.

  Fixes #15549.

  Will Bryant, Aaron Patterson

• Correctly create through records when created on a has many through association when using where.

  Fixes #19073.

  Sean Griffin

• Add SchemaMigration.create_table support for any unicode charsets with MySQL.

  Ryuta Kamizono

• PostgreSQL no longer disables user triggers if system triggers can't be disabled. Disabling user triggers does not fulfill what the method promises. Rails currently requires superuser privileges for this method.

  If you absolutely rely on this behavior, consider patching disable_referential_integrity.

  Yves Senn

• Restore aborted transaction state when disable_referential_integrity fails due to missing permissions.

  Toby Ovod-Everett, Yves Senn

• In PostgreSQL, print a warning message if disable_referential_integrity fails due to missing permissions.

  Andrey Nering, Yves Senn

• Allow a :limit option for MySQL bigint primary key support.

  Example:

  create_table :foos, id: :primary_key, limit: 8 do |t|
  end
  
  # or
  
  create_table :foos, id: false do |t|
    t.primary_key :id, limit: 8
  end
  

  Ryuta Kamizono

• belongs_to will now trigger a validation error by default if the association is not present. You can turn this off on a per-association basis with optional: true. (Note this new default only applies to new Rails apps that will be generated with config.active_record.belongs_to_required_by_default = true in initializer.)

  Josef Šimánek

• Fixed ActiveRecord::Relation#becomes! and changed_attributes issues for type columns.

  Fixes #17139.

  Miklos Fazekas

• Format the time string according to the precision of the time column.

  Ryuta Kamizono

• Allow a :precision option for time type columns.

  Ryuta Kamizono

• Add ActiveRecord::Base.suppress to prevent the receiver from being saved during the given block.

  For example, here's a pattern of creating notifications when new comments are posted. (The notification may in turn trigger an email, a push notification, or just appear in the UI somewhere):

  class Comment < ActiveRecord::Base
    belongs_to :commentable, polymorphic: true
    after_create -> { Notification.create! comment: self,
      recipients: commentable.recipients }
  end
  

  That's what you want the bulk of the time. A new comment creates a new Notification. There may be edge cases where you don't want that, like when copying a commentable and its comments, in which case write a concern with something like this:

  module Copyable
    def copy_to(destination)
      Notification.suppress do
        # Copy logic that creates new comments that we do not want triggering
        # notifications.
      end
    end
  end
  

  Michael Ryan

• :time option added for #touch.

  Fixes #18905.

  Hyonjee Joo

• Deprecate passing of start value to find_in_batches and find_each in favour of begin_at value.

  Vipul A M

• Add foreign_key_exists? method.

  Tõnis Simo

• Use SQL COUNT and LIMIT 1 queries for none? and one? methods if no block or limit is given, instead of loading the entire collection into memory. This applies to relations (e.g. User.all) as well as associations (e.g. account.users)

  # Before:
  
  users.none?
  # SELECT "users".* FROM "users"
  
  users.one?
  # SELECT "users".* FROM "users"
  
  # After:
  
  users.none?
  # SELECT 1 AS one FROM "users" LIMIT 1
  
  users.one?
  # SELECT COUNT(*) FROM "users"
  

  Eugene Gilburg

• Have enum perform type casting consistently with the rest of Active Record, such as where.

  Sean Griffin

• scoping no longer pollutes the current scope of sibling classes when using STI. e.x.

  StiOne.none.scoping do
    StiTwo.all
  end
  

  Fixes #18806.

  Sean Griffin

• remove_reference with foreign_key: true removes the foreign key before removing the column. This fixes a bug where it was not possible to remove the column on MySQL.

  Fixes #18664.

  Yves Senn

• find_in_batches now accepts an :end_at parameter that complements the :start parameter to specify where to stop batch processing.

  Vipul A M

• Fix a rounding problem for PostgreSQL timestamp columns.

  If a timestamp column has a precision specified, it needs to format according to that.

  Ryuta Kamizono

• Respect the database default charset for schema_migrations table.

  The charset of version column in schema_migrations table depends on the database default charset and collation rather than the encoding of the connection.

  Ryuta Kamizono

• Raise ArgumentError when passing nil or false to Relation#merge.

  These are not valid values to merge in a relation, so it should warn users early.

  Rafael Mendonça França

• Use SCHEMA instead of DB_STRUCTURE for specifying a structure file.

  This makes the db:structure tasks consistent with test:load_structure.

  Dieter Komendera

• Respect custom primary keys for associations when calling Relation#where

  Fixes #18813.

  Sean Griffin

• Fix several edge cases which could result in a counter cache updating twice or not updating at all for has_many and has_many :through.

  Fixes #10865.

  Sean Griffin

• Foreign keys added by migrations were given random, generated names. This meant a different structure.sql would be generated every time a developer ran migrations on their machine.

  The generated part of foreign key names is now a hash of the table name and column name, which is consistent every time you run the migration.

  Chris Sinjakli

• Validation errors would be raised for parent records when an association was saved when the parent had validate: false. It should not be the responsibility of the model to validate an associated object unless the object was created or modified by the parent.

  This fixes the issue by skipping validations if the parent record is persisted, not changed, and not marked for destruction.

  Fixes #17621.

  Eileen M. Uchitelle, Aaron Patterson

• Fix n+1 query problem when eager loading nil associations (fixes #18312)

  Sammy Larbi

• Change the default error message from can't be blank to must exist for the presence validator of the :required option on belongs_to/has_one associations.

  Henrik Nygren

• Fixed ActiveRecord::Relation#group method when an argument is an SQL reserved keyword:

  Example:

  SplitTest.group(:key).count
  Property.group(:value).count
  

  Bogdan Gusiev

• Added the #or method on ActiveRecord::Relation, allowing use of the OR operator to combine WHERE or HAVING clauses.

  Example:

  Post.where('id = 1').or(Post.where('id = 2'))
  # => SELECT * FROM posts WHERE (id = 1) OR (id = 2)
  

  Sean Griffin, Matthew Draper, Gael Muller, Olivier El Mekki

• Don't define autosave association callbacks twice from accepts_nested_attributes_for.

  Fixes #18704.

  Sean Griffin

• Integer types will no longer raise a RangeError when assigning an attribute, but will instead raise when going to the database.

  Fixes several vague issues which were never reported directly. See the commit message from the commit which added this line for some examples.

  Sean Griffin

• Values which would error while being sent to the database (such as an ASCII-8BIT string with invalid UTF-8 bytes on SQLite3), no longer error on assignment. They will still error when sent to the database, but you are given the ability to re-assign it to a valid value.

  Fixes #18580.

  Sean Griffin

• Don't remove join dependencies in Relation#exists?

  Fixes #18632.

  Sean Griffin

• Invalid values assigned to a JSON column are assumed to be nil.

  Fixes #18629.

  Sean Griffin

• Add ActiveRecord::Base#accessed_fields, which can be used to quickly discover which fields were read from a model when you are looking to only select the data you need from the database.

  Sean Griffin

• Introduce the :if_exists option for drop_table.

  Example:

  drop_table(:posts, if_exists: true)
  

  That would execute:

  DROP TABLE IF EXISTS posts
  

  If the table doesn't exist, if_exists: false (the default) raises an exception whereas if_exists: true does nothing.

  Cody Cutrer, Stefan Kanev, Ryuta Kamizono

• Don't run SQL if attribute value is not changed for update_attribute method.

  Prathamesh Sonpatki

• time columns can now get affected by time_zone_aware_attributes. If you have set config.time_zone to a value other than 'UTC', they will be treated as in that time zone by default in Rails 5.1. If this is not the desired behavior, you can set

  ActiveRecord::Base.time_zone_aware_types = [:datetime]
  

  A deprecation warning will be emitted if you have a :time column, and have not explicitly opted out.

  Fixes #3145.

  Sean Griffin

• Tests now run after_commit callbacks. You no longer have to declare uses_transaction ‘test name’ to test the results of an after_commit.

  after_commit callbacks run after committing a transaction whose parent is not joinable?: un-nested transactions, transactions within test cases, and transactions in console --sandbox.

  arthurnn, Ravil Bayramgalin, Matthew Draper

• nil as a value for a binary column in a query no longer logs as "", and instead logs as just "nil".

  Sean Griffin

• attribute_will_change! will no longer cause non-persistable attributes to be sent to the database.

  Fixes #18407.

  Sean Griffin

• Remove support for the protected_attributes gem.

  Carlos Antonio da Silva, Roberto Miranda

• Fix accessing of fixtures having non-string labels like Fixnum.

  Prathamesh Sonpatki

• Remove deprecated support to preload instance-dependent associations.

  Yves Senn

• Remove deprecated support for PostgreSQL ranges with exclusive lower bounds.

  Yves Senn

• Remove deprecation when modifying a relation with cached Arel. This raises an ImmutableRelation error instead.

  Yves Senn

• Added ActiveRecord::SecureToken in order to encapsulate generation of unique tokens for attributes in a model using SecureRandom.

  Roberto Miranda

• Change the behavior of boolean columns to be closer to Ruby's semantics.

  Before this change we had a small set of "truthy", and all others are "falsy".

  Now, we have a small set of "falsy" values and all others are "truthy" matching Ruby's semantics.

  Rafael Mendonça França

• Deprecate ActiveRecord::Base.errors_in_transactional_callbacks=.

  Rafael Mendonça França

• Change transaction callbacks to not swallow errors.

  Before this change any errors raised inside a transaction callback were getting rescued and printed in the logs.

  Now these errors are not rescued anymore and just bubble up, as the other callbacks.

  Rafael Mendonça França

• Remove deprecated sanitize_sql_hash_for_conditions.

  Rafael Mendonça França

• Remove deprecated Reflection#source_macro.

  Rafael Mendonça França

• Remove deprecated symbolized_base_class and symbolized_sti_name.

  Rafael Mendonça França

• Remove deprecated ActiveRecord::Base.disable_implicit_join_references=.

  Rafael Mendonça França

• Remove deprecated access to connection specification using a string accessor.

  Now all strings will be handled as a URL.

  Rafael Mendonça França

• Change the default null value for timestamps to false.

  Rafael Mendonça França

• Return an array of pools from connection_pools.

  Rafael Mendonça França

• Return a null column from column_for_attribute when no column exists.

  Rafael Mendonça França

• Remove deprecated serialized_attributes.

  Rafael Mendonça França

• Remove deprecated automatic counter caches on has_many :through.

  Rafael Mendonça França

• Change the way in which callback chains can be halted.

  The preferred method to halt a callback chain from now on is to explicitly throw(:abort). In the past, returning false in an Active Record before_ callback had the side effect of halting the callback chain. This is not recommended anymore and, depending on the value of the ActiveSupport.halt_callback_chains_on_return_false option, will either not work at all or display a deprecation warning.

  claudiob

• Clear query cache on rollback.

  Florian Weingarten

• Fix setting of foreign_key for through associations when building a new record.

  Fixes #12698.

  Ivan Antropov

• Improve dumping of the primary key. If it is not a default primary key, correctly dump the type and options.

  Fixes #14169, #16599.

  Ryuta Kamizono

• Format the datetime string according to the precision of the datetime field.

  Incompatible to rounding behavior between MySQL 5.6 and earlier.

  In 5.5, when you insert 2014-08-17 12:30:00.999999 the fractional part is ignored. In 5.6, it's rounded to 2014-08-17 12:30:01:

  http://bugs.mysql.com/bug.php?id=68760

  Ryuta Kamizono

• Allow a precision option for MySQL datetimes.

  Ryuta Kamizono

• Fixed automatic inverse_of for models nested in a module.

  Andrew McCloud

• Change ActiveRecord::Relation#update behavior so that it can be called without passing ids of the records to be updated.

  This change allows updating multiple records returned by ActiveRecord::Relation with callbacks and validations.

  # Before
  # ArgumentError: wrong number of arguments (1 for 2)
  Comment.where(group: 'expert').update(body: "Group of Rails Experts")
  
  # After
  # Comments with group expert updated with body "Group of Rails Experts"
  Comment.where(group: 'expert').update(body: "Group of Rails Experts")
  

  Prathamesh Sonpatki

• Fix reaping_frequency option when the value is a string.

  This usually happens when it is configured using DATABASE_URL.

  korbin

• Fix error message when trying to create an associated record and the foreign key is missing.

  Before this fix the following exception was being raised:

  NoMethodError: undefined method `val' for #<Arel::Nodes::BindParam:0x007fc64d19c218>
  

  Now the message is:

  ActiveRecord::UnknownAttributeError: unknown attribute 'foreign_key' for Model.
  

  Rafael Mendonça França

• Fix change detection problem for PostgreSQL bytea type and ArgumentError: string contains null byte exception with pg-0.18.

  Fixes #17680.

  Lars Kanis

• When a table has a composite primary key, the primary_key method for SQLite3 and PostgreSQL adapters was only returning the first field of the key. Ensures that it will return nil instead, as Active Record doesn't support composite primary keys.

  Fixes #18070.

  arthurnn

• validates_size_of / validates_length_of do not count records which are marked_for_destruction?.

  Fixes #7247.

  Yves Senn

• Ensure first! and friends work on loaded associations.

  Fixes #18237.

  Sean Griffin

• eager_load preserves readonly flag for associations.

  Fixes #15853.

  Takashi Kokubun

• Provide :touch option to save() to accommodate saving without updating timestamps.

  Fixes #18202.

  Dan Olson

• Provide a more helpful error message when an unsupported class is passed to serialize.

  Fixes #18224.

  Sean Griffin

• Add bigint primary key support for MySQL.

  Example:

  create_table :foos, id: :bigint do |t|
  end
  

  Ryuta Kamizono

• Support for any type of primary key.

  Fixes #14194.

  Ryuta Kamizono

• Dump the default nil for PostgreSQL UUID primary key.

  Ryuta Kamizono

• Add a :foreign_key option to references and associated migration methods. The model and migration generators now use this option, rather than the add_foreign_key form.

  Sean Griffin

• Don't raise when writing an attribute with an out-of-range datetime passed by the user.

  Grey Baker

• Replace deprecated ActiveRecord::Tasks::DatabaseTasks#load_schema with ActiveRecord::Tasks::DatabaseTasks#load_schema_for.

  Yves Senn

• Fix bug with ActiveRecord::Type::Numeric that caused negative values to be marked as having changed when set to the same negative value.

  Fixes #18161.

  Daniel Fox

• Introduce force: :cascade option for create_table. Using this option will recreate tables even if they have dependent objects (like foreign keys). db/schema.rb now uses force: :cascade. This makes it possible to reload the schema when foreign keys are in place.

  Matthew Draper, Yves Senn

• db:schema:load and db:structure:load no longer purge the database before loading the schema. This is left for the user to do. db:test:prepare will still purge the database.

  Fixes #17945.

  Yves Senn

• Fix undesirable RangeError by Type::Integer. Add Type::UnsignedInteger.

  Ryuta Kamizono

• Add foreign_type option to has_one and has_many association macros.

  This option enables to define the column name of associated object's type for polymorphic associations.

  Ulisses Almeida, Kassio Borges

• Remove deprecated behavior allowing nested arrays to be passed as query values.

  Melanie Gilman

• Deprecate passing a class as a value in a query. Users should pass strings instead.

  Melanie Gilman

• add_timestamps and remove_timestamps now properly reversible with options.

  Noam Gagliardi-Rabinovich

• ActiveRecord::ConnectionAdapters::ColumnDumper#column_spec and ActiveRecord::ConnectionAdapters::ColumnDumper#prepare_column_options no longer have a types argument. They should access connection#native_database_types directly.

  Yves Senn

Please check 4-2-stable for previous changes.