Rails 4.0.1 (November 01, 2013)

• NullRelation#pluck takes a list of columns

  The method signature in NullRelation was updated to mimic that in
  Calculations.

  Derek Prior

• scope_chain should not be mutated for other reflections.

  Currently scope_chain uses same array for building different
  scope_chain for different associations. During processing
  these arrays are sometimes mutated and because of in-place
  mutation the changed scope_chain impacts other reflections.

  Fix is to dup the value before adding to the scope_chain.

  Fixes #3882.

  Neeraj Singh

• Prevent the inversed association from being reloaded on save.

  Fixes #9499.

  Dmitry Polushkin

• Relation#order quotes the column name if you pass a Symbol.
  Fixes #11870.

  Example:

  # Before
  Post.order(:id).to_sql == ‘… ORDER BY “posts”.id ASC’

  # After
  Post.order(:id).to_sql == ‘… ORDER BY “posts”.“id” ASC’

  Yves Senn

• Generate subquery for Relation if it passed as array condition for where
  method.

  Example:

  # Before
  Blog.where(‘id in (?)’, Blog.where(id: 1))
  # => SELECT “blogs”.* FROM “blogs” WHERE “blogs”.“id” = 1
  # => SELECT “blogs”.* FROM “blogs” WHERE (id IN (1))

  # After
  Blog.where(‘id in (?)’, Blog.where(id: 1).select(:id))
  # => SELECT “blogs”.* FROM “blogs”
  # WHERE “blogs”.“id” IN (SELECT “blogs”.“id” FROM “blogs” WHERE “blogs”.“id” = 1)

  Fixes #12415.

  Paul Nikitochkin

• For missed association exception message
  which is raised in ActiveRecord::Associations::Preloader class
  added owner record class name in order to simplify to find problem code.

  Paul Nikitochkin

• Fixes bug when using includes combined with select, the select statement was overwritten.

  Fixes #11773.

  Edo Balvers

• Objects instantiated using a null relationship will now retain the
  attributes of the where clause.

  Fixes #11676, #11675, #11376.

  Paul Nikitochkin, Peter Brown, Nthalk

• Fixed ActiveRecord::Associations::CollectionAssociation#find
  when using has_many association with :inverse_of and finding an array of one element,
  it should return an array of one element too.

  arthurnn

• Callbacks on has_many should access the in memory parent if a inverse_of is set.

  arthurnn

• Migration dump UUID default functions to schema.rb.

  Fixes #10751.

  kennyj

• Fixed a bug in ActiveRecord::Associations::CollectionAssociation#find_by_scan
  when using has_many association with :inverse_of option and UUID primary key.

  Fixes #10450.

  kennyj

• Fix: joins association, with defined in the scope block constraints by using several
  where constraints and at least of them is not Arel::Nodes::Equality,
  generates invalid SQL expression.

  Fixes: #11963

  Paul Nikitochkin

• Make possible to run SQLite rake tasks without the Rails constant defined.

  Damien Mathieu

• Allow Relation#from to accept other relations with bind values.

  Ryan Wallace

• Make find_in_batches and find_each work without a logger.

  Dmitry Polushkin

• Fix inserts with prepared statements disabled.

  Fixes #12023.

  Rafael Mendonça França

• Setting a has_one association on a new record no longer causes an empty
  transaction.

  Dylan Thacker-Smith

• Fix AR::Relation#merge sometimes failing to preserve readonly(false) flag.

  thedarkone

• PostgreSQL adapter recognizes negative money values formatted with
  parentheses (eg. ($1.25) # => -1.25)).
  Fixes #11899.

  • Yves Senn*

• Do not load all child records for inverse case.

  currently post.comments.find(Comment.first.id) would load all
  comments for the given post to set the inverse association.

  This has a huge performance penalty. Because if post has 100k
  records and all these 100k records would be loaded in memory
  even though the comment id was supplied.

  Fix is to use in-memory records only if loaded? is true. Otherwise
  load the records using full sql.

  Fixes #10509.

  Neeraj Singh

• ActiveRecord::FinderMethods#exists? returns true/false in all cases.

  Xavier Noria

• Load fixtures from linked folders.

  Kassio Borges

• Create a directory for sqlite3 file if not present on the system.

  Richard Schneeman

• Removed redundant override of xml column definition for PG,
  in order to use xml column type instead of text.

  Paul Nikitochkin, Michael Nikitochkin

• Revert ActiveRecord::Relation#order change that make new order
  prepend the old one.

  Before:

  User.order(“name asc”).order(“created_at desc”)
  # SELECT * FROM users ORDER BY created_at desc, name asc

  After:

  User.order(“name asc”).order(“created_at desc”)
  # SELECT * FROM users ORDER BY name asc, created_at desc

  This also affects order defined in default_scope or any kind of associations.

  Rafael Mendonça França

• When using optimistic locking, update was not passing the column to quote_value
  to allow the connection adapter to properly determine how to quote the value. This was
  affecting certain databases that use specific column types.

  Fixes #6763.

  Alfred Wong

• change_column for PostgreSQL adapter respects the :array option.

  Yves Senn

• Fixes bug introduced by #3329. Now, when autosaving associations,
  deletions happen before inserts and saves. This prevents a
  ‘duplicate unique value’ database error that would occur if a record being created had
  the same value on a unique indexed field as that of a record being destroyed.

  Johnny Holton

• Flatten merged join values before building the joins.

  While joining values special treatment is given to string values.
  By flattening the array it ensures that string values are detected
  as strings and not arrays.

  Fixes #10669.

  Neeraj Singh and iwiznia

• Remove extra select and update queries on save/touch/destroy Active Record model
  with belongs to reflection with option touch: true.

  Fixes #11288.

  Paul Nikitochkin

• Support array as root element in JSON fields.

  Alexey Noskov & Francesco Rodriguez

• Apply default scope when joining associations. For example:

  class Post < ActiveRecord::Base
  default_scope -> { where published: true }
  end

  class Comment
  belongs_to :post
  end

  When calling Comment.joins(:post), we expect to receive only
  comments on published posts, since that is the default scope for
  posts.

  Before this change, the default scope from Post was not applied,
  so we’d get comments on unpublished posts.

  Jon Leighton

• inspect on Active Record model classes does not initiate a
  new connection. This means that calling inspect, when the
  database is missing, will no longer raise an exception.

  Fixes #10936.

  Example:

  Author.inspect # => “Author(no database connection)”

  Yves Senn

• Fix mysql2 adapter raises the correct exception when executing a query on a
  closed connection.

  Yves Senn

• Fix the :primary_key option for has_many associations.

  Fixes #10693.

  Yves Senn

• Fix bug where tiny types are incorectly coerced as booleand when the length is more than 1.

  Fixes #10620.

  Aaron Patterson

• Also support extensions in PostgreSQL 9.1. This feature has been supported since 9.1.

  kennyj

• Deprecate ConnectionAdapters::SchemaStatements#distinct,
  as it is no longer used by internals.

  *Ben Woosley#

• Remove not needed bind variables. Port of commit #5082345.

  Fixes #10958.

  Neeraj Singh

• Confirm a record has not already been destroyed before decrementing counter cache.

  Ben Tucker

• Fixed a bug in ActiveRecord#sanitize_sql_hash_for_conditions in which
  self.class is an argument to PredicateBuilder#build_from_hash
  causing PredicateBuilder to call non-existent method
  Class#reflect_on_association.

  Zach Ohlgren

• While removing index if column option is missing then raise IrreversibleMigration exception.

  Following code should raise IrreversibleMigration. But the code was
  failing since options is an array and not a hash.

  def change
  change_table :users do |t|
  t.remove_index [:name, :email]
  end
  end

  Fix was to check if the options is a Hash before operating on it.

  Fixes #10419.

  Neeraj Singh

Rails 4.0.0 (June 25, 2013)

• Fix add_column with array option when using PostgreSQL. Fixes #10432

• Do not overwrite manually built records during one-to-one nested attribute assignment

  For one-to-one nested associations, if you build the new (in-memory)
  child object yourself before assignment, then the NestedAttributes
  module will not overwrite it, e.g.:

  class Member < ActiveRecord::Base
  has_one :avatar
  accepts_nested_attributes_for :avatar

  def avatar
  super || build_avatar(width: 200)
  end
  end

  member = Member.new
  member.avatar_attributes = {icon: ‘sad’}
  member.avatar.width # => 200

  Olek Janiszewski

• fixes bug introduced by #3329. Now, when autosaving associations,
  deletions happen before inserts and saves. This prevents a ‘duplicate
  unique value’ database error that would occur if a record being created had
  the same value on a unique indexed field as that of a record being destroyed.

  Adam Anderson

• Fix pending migrations error when loading schema and ActiveRecord::Base.table_name_prefix
  is not blank.

  Call assume_migrated_upto_version on connection to prevent it from first
  being picked up in method_missing.

  In the base class, Migration, method_missing expects the argument to be a
  table name, and calls proper_table_name on the arguments before sending to
  connection. If table_name_prefix or table_name_suffix is used, the schema
  version changes to prefix_version_suffix, breaking rake test:prepare.

  Fixes #10411.

  Kyle Stevens

• Mute psql output when running rake db:schema:load.

  Godfrey Chan

• Trigger a save on has_one association=(associate) when the associate contents have changed.

  Fix #8856.

  Chris Thompson

• Allow to use databases.rake tasks without having Rails.application.

  Piotr Sarnacki

• Fix a SystemStackError problem when using time zone aware or serialized attributes.
  In current implementation, we reuse column_types argument when initiating an instance.
  If an instance has serialized or time zone aware attributes, column_types is
  wrapped multiple times in decorate_columns method. Thus the above error occurs.

  Dan Erikson & kennyj

• Fix for a regression bug in which counter cache columns were not being updated
  when record was pushed into a has_many association. For example:

  Post.first.comments << Comment.create

  Fixes #3891.

  Matthew Robertson

• If a model was instantiated from the database using select, respond_to?
  returns false for non-selected attributes. For example:

  post = Post.select(:title).first
  post.respond_to?(:body) # => false

  post = Post.select(‘title as post_title’).first
  post.respond_to?(:title) # => false

  Fixes #4208.

  Neeraj Singh

• Run rake migrate:down & rake migrate:up in transaction if database supports.

  Alexander Bondarev

• 0x prefix must be added when assigning hexadecimal string into bit column in PostgreSQL.

  kennyj

• Added Statement Cache to allow the caching of a single statement. The cache works by
  duping the relation returned from yielding a statement, which allows skipping the AST
  building phase for following executes. The cache returns results in array format.

  Example:

  cache = ActiveRecord::StatementCache.new do
  Book.where(name: “my book”).limit(100)
  end

  books = cache.execute

  The solution attempts to get closer to the speed of find_by_sql but still maintaining
  the expressiveness of the Active Record queries.

  Olli Rissanen

• Preserve context while merging relations with join information.

  class Comment < ActiveRecord::Base
  belongs_to :post
  end

  class Author < ActiveRecord::Base
  has_many :posts
  end

  class Post < ActiveRecord::Base
  belongs_to :author
  has_many :comments
  end

  Comment.joins(:post).merge(Post.joins(:author).merge(Author.where(:name => "Joe Blogs"))).all
  would fail with
  ActiveRecord::ConfigurationError: Association named 'author' was not found on Comment.

  It is failing because all is being called on relation which looks like this after all
  the merging: `{:joins=>[:post, :author], :where=>[# ‘gin’)

  Stefan Huber and Doabit

• After extraction of mass-assignment attributes (which protects [id, type]
  by default) we can pass id to update_attributes and it will update
  another record because id will be used in where statement. We never have
  to change id in where statement because we try to set/replace fields for
  already loaded record but we have to try to set new id for that record.

  Dmitry Vorotilin

• Models with multiple counter cache associations now update correctly on destroy.
  See #7706.

  Ian Young

• If :inverse_of is true on an association, then when one calls find() on
  the association, Active Record will first look through the in-memory objects
  in the association for a particular id. Then, it will go to the DB if it
  is not found. This is accomplished by calling find_by_scan in
  collection associations whenever options[:inverse_of] is not nil.
  Fixes #9470.

  John Wang

• rake db:create does not change permissions of the MySQL root user.
  Fixes #8079.

  Yves Senn

• The length of the version column in the schema_migrations table
  created by the mysql2 adapter is 191 if the encoding is “utf8mb4”.

  The “utf8” encoding in MySQL has support for a maximum of 3 bytes per character,
  and only contains characters from the BMP. The recently added
  utf8mb4
  encoding extends the support to four bytes. As of this writing, said encoding
  is supported in the betas of the mysql2 gem.

  Setting the encoding to “utf8mb4” has
  a few implications.
  This change addresses the max length for indexes, which is 191 instead of 255.

  Xavier Noria

• Counter caches on associations will now stay valid when attributes are
  updated (not just when records are created or destroyed), for example,
  when calling update_attributes. The following code now works:

  class Comment < ActiveRecord::Base
  belongs_to :post, counter_cache: true
  end

  class Post < ActiveRecord::Base
  has_many :comments
  end

  post = Post.create
  comment = Comment.create

  post.comments << comment
  post.save.reload.comments_count # => 1
  comment.update_attributes(post_id: nil)

  post.save.reload.comments_count # => 0

  Updating the id of a belongs_to object with the id of a new object will
  also keep the count accurate.

  John Wang

• Referencing join tables implicitly was deprecated. There is a
  possibility that these deprecation warnings are shown even if you
  don’t make use of that feature. You can now disable the feature entirely.
  Fixes #9712.

  Example:

  # in your configuration
  config.active_record.disable_implicit_join_references = true

  # or directly
  ActiveRecord::Base.disable_implicit_join_references = true

  Yves Senn

• The :distinct option for Relation#count is deprecated. You
  should use Relation#distinct instead.

  Example:

  # Before
  Post.select(:author_name).count(distinct: true)

  # After
  Post.select(:author_name).distinct.count

  Yves Senn

• Rename Relation#uniq to Relation#distinct. #uniq is still
  available as an alias but we encourage to use #distinct instead.
  Also Relation#uniq_value is aliased to Relation#distinct_value,
  this is a temporary solution and you should migrate to distinct_value.

  Yves Senn

• Fix quoting for sqlite migrations using copy_table_contents with binary
  columns.

  These would fail with “SQLite3::SQLException: unrecognized token” because
  the column was not being passed to quote so the data was not quoted
  correctly.

  Matthew M. Boedicker

• Promotes change_column_null to the migrations API. This macro sets/removes
  NOT NULL constraints, and accepts an optional argument to replace existing
  NULLs if needed. The adapters for SQLite, MySQL, PostgreSQL, and (at least)
  Oracle, already implement this method.

  Xavier Noria

• Uniqueness validation allows you to pass :conditions to limit
  the constraint lookup.

  Example:

  validates_uniqueness_of :title, conditions: -> { where(‘approved = ?’, true) }

  Mattias Pfeiffer + Yves Senn

• connection is deprecated as an instance method.
  This allows end-users to have a connection method on their models
  without clashing with Active Record internals.

  Ben Moss

• When copying migrations, preserve their magic comments and content encoding.

  OZAWA Sakuro

• Fix subclass_from_attrs when eager_load is false. It cannot find
  subclass because all classes are loaded automatically when it needs.

  Dmitry Vorotilin

• When :name option is provided to remove_index, use it if there is no
  index by the conventional name.

  For example, previously if an index was removed like so
  remove_index :values, column: :value, name: 'a_different_name'
  the generated SQL would not contain the specified index name,
  and hence the migration would fail.
  Fixes #8858.

  Ezekiel Smithburg

• Created block to by-pass the prepared statement bindings.
  This will allow to compose fragments of large SQL statements to
  avoid multiple round-trips between Ruby and the DB.

  Example:

  sql = Post.connection.unprepared_statement do
  Post.first.comments.to_sql
  end

  Cédric Fabianski

• Change the semantics of combining scopes to be the same as combining
  class methods which return scopes. For example:

  class User < ActiveRecord::Base
  scope :active, -> { where state: ‘active’ }
  scope :inactive, -> { where state: ‘inactive’ }
  end

  class Post < ActiveRecord::Base
  def self.active
  where state: ‘active’
  end

  def self.inactive
  where state: ‘inactive’
  end
  end

  ### BEFORE ###

  User.where(state: ‘active’).where(state: ‘inactive’)
  # => SELECT * FROM users WHERE state = ‘active’ AND state = ‘inactive’

  User.active.inactive
  # => SELECT * FROM users WHERE state = ‘inactive’

  Post.active.inactive
  # => SELECT * FROM posts WHERE state = ‘active’ AND state = ‘inactive’

  ### AFTER ###

  User.active.inactive
  # => SELECT * FROM posts WHERE state = ‘active’ AND state = ‘inactive’

  Before this change, invoking a scope would merge it into the current
  scope and return the result. Relation#merge applies “last where
  wins” logic to de-duplicate the conditions, but this lead to
  confusing and inconsistent behaviour. This fixes that.

  If you really do want the “last where wins” logic, you can opt-in to
  it like so:

  User.active.merge(User.inactive)

  Fixes #7365.

  Neeraj Singh and Jon Leighton

• Expand #cache_key to consult all relevant updated timestamps.

  Previously only updated_at column was checked, now it will
  consult other columns that received updated timestamps on save,
  such as updated_on. When multiple columns are present it will
  use the most recent timestamp.
  Fixes #9033.

  Brendon Murphy

• Throw NotImplementedError when trying to instantiate ActiveRecord::Base or an abstract class.

  Aaron Weiner

• Warn when rake db:structure:dump with a MySQL database and
  mysqldump is not in the PATH or fails.
  Fixes #9518.

  Yves Senn

• Remove connection#structure_dump, which is no longer used. Yves Senn

• Make it possible to execute migrations without a transaction even
  if the database adapter supports DDL transactions.
  Fixes #9483.

  Example:

  class ChangeEnum < ActiveRecord::Migration
  disable_ddl_transaction!

  def up
  execute “ALTER TYPE model_size ADD VALUE ‘new_value’”
  end
  end

  Yves Senn

• Assigning “0.0” to a nullable numeric column does not make it dirty.
  Fixes #9034.

  Example:

  product = Product.create price: 0.0
  product.price = ‘0.0’
  product.changed? # => false (this used to return true)
  product.changes # => {} (this used to return { price: [0.0, 0.0] })

  Yves Senn

• Added functionality to unscope relations in a relations chain. For
  instance, if you are passed in a chain of relations as follows:

  User.where(name: “John”).order(‘id DESC’)

  but you want to get rid of order, then this feature allows you to do:

  User.where(name: “John”).order(‘id DESC’).unscope(:order)
  == User.where(name: “John”)

  The .unscope() function is more general than the .except() method because
  .except() only works on the relation it is acting on. However, .unscope()
  works for any relation in the entire relation chain.

  John Wang

• PostgreSQL timestamp with time zone (timestamptz) datatype now returns a
  ActiveSupport::TimeWithZone instance instead of a string

  Troy Kruthoff

• The #append method for collection associations behaves like<<.
  #prepend is not defined and << or #append should be used.
  Fixes #7364.

  Yves Senn

• Added support for creating a table via Rails migration generator.
  For example,

  rails g migration create_books title:string content:text

  will generate a migration that creates a table called books with
  the listed attributes, without creating a model.

  Sammy Larbi

• Fix bug that raises the wrong exception when the exception handled by PostgreSQL adapter
  doesn’t respond to #result.
  Fixes #8617.

  kennyj

• Support PostgreSQL specific column types when using change_table.
  Fixes #9480.

  Example:

  change_table :authors do |t|
  t.hstore :books
  t.json :metadata
  end

  Yves Senn

• Revert 408227d9c5ed7d, ‘quote numeric’. This introduced some regressions.

  Steve Klabnik

• Fix calculation of db_runtime property in
  ActiveRecord::Railties::ControllerRuntime#cleanup_view_runtime.
  Previously, after raising ActionView::MissingTemplate, db_runtime was
  not populated.
  Fixes #9215.

  Igor Fedoronchuk

• Do not try to touch invalid (and thus not persisted) parent record
  for a belongs_to :parent, touch: true association

  Olek Janiszewski

• Fix when performing an ordered join query. The bug only
  affected queries where the order was given with a symbol.
  Fixes #9275.

  Example:

  # This will expand the order :name to “authors”.name.
  Author.joins(:books).where(‘books.published = 1’).order(:name)

• Fix overriding of attributes by default_scope on ActiveRecord::Base#dup.

  Hiroshige UMINO

• Update queries now use prepared statements.

  Olli Rissanen

• Fixing issue #8345. Now throwing an error when one attempts to touch a
  new object that has not yet been persisted. For instance:

  Example:

  ball = Ball.new
  ball.touch :updated_at # => raises error

  It is not until the ball object has been persisted that it can be touched.
  This follows the behavior of update_column.

  John Wang

• Preloading ordered has_many :through associations no longer applies
  invalid ordering to the :through association.
  Fixes #8663.

  Yves Senn

• The auto explain feature has been removed. This feature was
  activated by configuring config.active_record.auto_explain_threshold_in_seconds.
  The configuration option was deprecated and has no more effect.

  You can still use ActiveRecord::Relation#explain to see the EXPLAIN output for
  any given relation.

  Yves Senn

• The :on option for after_commit and after_rollback now
  accepts an Array of actions.
  Fixes #988.

  Example:

  after_commit :update_cache on: [:create, :update]

  Yves Senn

• Rename related indexes on rename_table and rename_column. This
  does not affect indexes with custom names.

  Yves Senn

• Prevent the creation of indices with too long names, which cause
  internal operations to fail (sqlite3 adapter only). The method
  allowed_index_name_length defines the length limit enforced by
  rails. It’s value defaults to index_name_length but can vary per adapter.
  Fixes #8264.

  Yves Senn

• Fixing issue #776.

  Memory bloat in transactions is handled by having the transaction hold only
  the AR objects which it absolutely needs to know about. These are the AR
  objects with callbacks (they need to be updated as soon as something in the
  transaction occurs).

  All other AR objects can be updated lazily by keeping a reference to a
  TransactionState object. If an AR object gets inside a transaction, then
  the transaction will add its TransactionState to the AR object. When the
  user makes a call to some attribute on an AR object (which has no
  callbacks) associated with a transaction, the AR object will call the
  sync_with_transaction_state method and make sure it is up to date with the
  transaction. After it has synced with the transaction state, the AR object
  will return the attribute that was requested.

  Most of the logic in the changes are used to handle multiple transactions,
  in which case the AR object has to recursively follow parent pointers of
  TransactionState objects.

  John Wang

• Descriptive error message when the necessary AR adapter gem was not found.
  Fixes #7313.

  Yves Senn

• Active Record now raises an error when blank arguments are passed to query
  methods for which blank arguments do not make sense.

  Example:

  Post.includes() # => raises error

  John Wang

• Simplified type casting code for timezone aware attributes to use the
  in_time_zone method if it is available. This introduces a subtle change
  of behavior when using Date instances as they are directly converted to
  ActiveSupport::TimeWithZone instances without first being converted to
  Time instances. For example:

  # Rails 3.2 behavior
  >> Date.today.to_time.in_time_zone
  => Wed, 13 Feb 2013 07:00:00 UTC +00:00

  # Rails 4.0 behavior
  >> Date.today.in_time_zone
  => Wed, 13 Feb 2013 00:00:00 UTC +00:00

  On the plus side it now behaves the same whether you pass a String date
  or an actual Date instance. For example:

  # Rails 3.2 behavior
  >> Date.civil(2013, 2, 13).to_time.in_time_zone
  => Wed, 13 Feb 2013 07:00:00 UTC +00:00
  >> Time.zone.parse(“2013-02-13”)
  => Wed, 13 Feb 2013 00:00:00 UTC +00:00

  # Rails 4.0 behavior
  >> Date.civil(2013, 2, 13).in_time_zone
  => Wed, 13 Feb 2013 00:00:00 UTC +00:00
  >> “2013-02-13”.in_time_zone
  => Wed, 13 Feb 2013 00:00:00 UTC +00:00

  If you need the old behavior you can convert the dates to times manually.
  For example:

  >> Post.new(created_at: Date.today).created_at
  => Wed, 13 Feb 2013 00:00:00 UTC +00:00

  >> Post.new(created_at: Date.today.to_time).created_at
  => Wed, 13 Feb 2013 07:00:00 UTC +00:00

  Andrew White

• Preloading has_many :through associations with conditions won’t
  cache the :through association. This will prevent invalid
  subsets to be cached.
  Fixes #8423.

  Example:

  class User
  has_many :posts
  has_many :recent_comments, -> { where(‘created_at > ?’, 1.week.ago) }, :through => :posts
  end

  a_user = User.includes(:recent_comments).first

  # This is preloaded.
  a_user.recent_comments

  # This is not preloaded, fetched now.
  a_user.posts

  Yves Senn

• Don’t run after_commit callbacks when creating through an association
  if saving the record fails.

  James Miller

• Allow store accessors to be overridden like other attribute methods, e.g.:

  class User < ActiveRecord::Base
  store :settings, accessors: [ :color, :homepage ], coder: JSON

  def color
  super || ‘red’
  end
  end

  Sergey Nartimov

• Quote numeric values being compared to non-numeric columns. Otherwise,
  in some database, the string column values will be coerced to a numeric
  allowing 0, 0.0 or false to match any string starting with a non-digit.

  Example:

  App.where(apikey: 0) # => SELECT * FROM users WHERE apikey = ‘0’

  Dylan Smith

• Schema dumper supports dumping the enabled database extensions to schema.rb
  (currently only supported by PostgreSQL).

  Justin George

• The database adapters now converts the options passed thought DATABASE_URL
  environment variable to the proper Ruby types before using. For example, SQLite requires
  that the timeout value is an integer, and PostgreSQL requires that the
  prepared_statements option is a boolean. These now work as expected:

  Example:

  DATABASE_URL=sqlite3://localhost/test_db?timeout=500
  DATABASE_URL=postgresql://localhost/test_db?prepared_statements=false

  Aaron Stone + Rafael Mendonça França

• Relation#merge now only overwrites where values on the LHS of the
  merge. Consider:

  left = Person.where(age: [13, 14, 15])
  right = Person.where(age: [13, 14]).where(age: [14, 15])

  left results in the following SQL:

  WHERE age IN (13, 14, 15)

  right results in the following SQL:

  WHERE age IN (13, 14) AND age IN (14, 15)

  Previously, left.merge(right) would result in all but the last
  condition being removed:

  WHERE age IN (14, 15)

  Now it results in the LHS condition(s) for age being removed, but
  the RHS remains as it is:

  WHERE age IN (13, 14) AND age IN (14, 15)

  Jon Leighton

• Fix handling of dirty time zone aware attributes

  Previously, when time_zone_aware_attributes were enabled, after
  changing a datetime or timestamp attribute and then changing it back
  to the original value, changed_attributes still tracked the
  attribute as changed. This caused [attribute]_changed? and
  changed? methods to return true incorrectly.

  Example:

  in_time_zone ‘Paris’ do
  order = Order.new
  original_time = Time.local(2012, 10, 10)
  order.shipped_at = original_time
  order.save
  order.changed? # => false

  # changing value
  order.shipped_at = Time.local(2013, 1, 1)
  order.changed? # => true

  # reverting to original value
  order.shipped_at = original_time
  order.changed? # => false, used to return true
  end

  Lilibeth De La Cruz

• When #count is used in conjunction with #uniq we perform count(:distinct => true).
  Fixes #6865.

  Example:

  relation.uniq.count # => SELECT COUNT(DISTINCT *)

  Yves Senn + Kaspar Schiess

• PostgreSQL ranges type support. Includes: int4range, int8range,
  numrange, tsrange, tstzrange, daterange

  Ranges can be created with inclusive and exclusive bounds.

  Example:

  create_table :Room do |t|
  t.daterange :availability
  end

  Room.create(availability: (Date.today..Float::INFINITY))
  Room.first.availability # => Wed, 19 Sep 2012..Infinity

  One thing to note: Range class does not support exclusive lower
  bound.

  Alexander Grebennik

• Added a state instance variable to each transaction. Will allow other objects
  to know whether a transaction has been committed or rolled back.

  John Wang

• Collection associations #empty? always respects built records.
  Fixes #8879.

  Example:

  widget = Widget.new
  widget.things.build
  widget.things.empty? # => false

  Yves Senn

• Support for PostgreSQL’s ltree data type.

  Rob Worley

• Fix undefined method to_i when calling new on a scope that uses an
  Array; Fix FloatDomainError when setting integer column to NaN.
  Fixes #8718, #8734, #8757.

  Jason Stirk + Tristan Harward

• Rename update_attributes to update, keep update_attributes as an alias for update method.
  This is a soft-deprecation for update_attributes, although it will still work without any
  deprecation message in 4.0 is recommended to start using update since update_attributes will be
  deprecated and removed in future versions of Rails.

  Amparo Luna + Guillermo Iguaran

• after_commit and after_rollback now validate the :on option and raise an ArgumentError
  if it is not one of :create, :destroy or :update

  Pascal Friederich

• Improve ways to write change migrations, making the old up & down methods no longer necessary.

  • The methods drop_table and remove_column are now reversible, as long as the necessary information is given. The method remove_column used to accept multiple column names; instead use remove_columns (which is not reversible). The method change_table is also reversible, as long as its block doesn’t call remove, change or change_default
  • New method reversible makes it possible to specify code to be run when migrating up or down. See the Guide on Migration
  • New method revert will revert a whole migration or the given block. If migrating down, the given migration / block is run normally. See the Guide on Migration

  Attempting to revert the methods execute, remove_columns and change_column will now
  raise an IrreversibleMigration instead of actually executing them without any output.

  Marc-André Lafortune

• Serialized attributes can be serialized in integer columns.
  Fixes #8575.

  Rafael Mendonça França

• Keep index names when using alter_table with sqlite3.
  Fixes #3489.

  Yves Senn

• Add ability for PostgreSQL adapter to disable user triggers in disable_referential_integrity.
  Fixes #5523.

  Gary S. Weaver

• Added support for validates_uniqueness_of in PostgreSQL array columns.
  Fixes #8075.

  Pedro Padron

• Allow int4range and int8range columns to be created in PostgreSQL and properly convert to/from database.

  Alexey Vasiliev aka leopard

• Do not log the binding values for binary columns.

  Matthew M. Boedicker

• Fix counter cache columns not updated when replacing has_many :through
  associations.

  Matthew Robertson

• Recognize migrations placed in directories containing numbers and ‘rb’.
  Fixes #8492.

  Yves Senn

• Add ActiveRecord::Base.cache_timestamp_format class attribute to control
  the format of the timestamp value in the cache key. Defaults to :nsec.
  Fixes #8195.

  Rafael Mendonça França

• Session variables can be set for the mysql, mysql2, and postgresql adapters
  in the variables: parameter in config/database.yml. The key-value pairs of this
  hash will be sent in a SET key = value query on new database connections. See also:
  http://dev.mysql.com/doc/refman/5.0/en/set-statement.html
  http://www.postgresql.org/docs/8.3/static/sql-set.html

  Aaron Stone

• Allow setting of all libpq connection parameters through the PostgreSQL adapter. See also:
  http://www.postgresql.org/docs/9.2/static/libpq-connect.html#LIBPQ-PARAMKEYWORDS

  Lars Kanis

• Allow Relation#where with no arguments to be chained with new not query method.

  Example:

  Developer.where.not(name: ‘Aaron’)

  Akira Matsuda

• Unscope update_column(s) query to ignore default scope.

  When applying default_scope to a class with a where clause, using
  update_column(s) could generate a query that would not properly update
  the record due to the where clause from the default_scope being applied
  to the update query.

  class User < ActiveRecord::Base
  default_scope -> { where(active: true) }
  end

  user = User.first
  user.active = false
  user.save!

  user.update_column(:active, true) # => false

  In this situation we want to skip the default_scope clause and just
  update the record based on the primary key. With this change:

  user.update_column(:active, true) # => true

  Fixes #8436.

  Carlos Antonio da Silva

• SQLite adapter no longer corrupts binary data if the data contains %00.

  Chris Feist

• Fix performance problem with primary_key method in PostgreSQL adapter when having many schemas.
  Uses pg_constraint table instead of pg_depend table which has many records in general.
  Fixes #8414.

  kennyj

• Do not instantiate intermediate Active Record objects when eager loading.
  These records caused after_find to run more than expected.
  Fixes #3313.

  Yves Senn

• Add STI support to init and building associations.
  Allows you to do BaseClass.new(type: "SubClass") as well as
  parent.children.build(type: "SubClass") or parent.build_child
  to initialize an STI subclass. Ensures that the class name is a
  valid class and that it is in the ancestors of the super class
  that the association is expecting.

  Jason Rush

• Observers was extracted from Active Record as rails-observers gem.

  Rafael Mendonça França

• Ensure that associations take a symbol argument. Steve Klabnik

• Fix dirty attribute checks for TimeZoneConversion with nil and blank
  datetime attributes. Setting a nil datetime to a blank string should not
  result in a change being flagged.
  Fixes #8310.

  Alisdair McDiarmid

• Prevent mass assignment to the type column of polymorphic associations when using build
  Fixes #8265.

  Yves Senn

• Deprecate calling Relation#sum with a block. To perform a calculation over
  the array result of the relation, use to_a.sum(&block).

  Carlos Antonio da Silva

• Fix PostgreSQL adapter to handle BC timestamps correctly

  HistoryEvent.create!(name: “something”, occured_at: Date.new(0) - 5.years)

  Bogdan Gusiev

• When running migrations on PostgreSQL, the :limit option for binary and text columns is silently dropped.
  Previously, these migrations caused sql exceptions, because PostgreSQL doesn’t support limits on these types.

  Victor Costan

• Don’t change STI type when calling ActiveRecord::Base#becomes.
  Add ActiveRecord::Base#becomes! with the previous behavior.

  See #3023 for more information.

  Thomas Hollstegge

• rename_index can be used inside a change_table block.

  change_table :accounts do |t|
  t.rename_index :user_id, :account_id
  end

  Jarek Radosz

• #pluck can be used on a relation with select clause. Fix #7551

  Example:

  Topic.select([:approved, :id]).order(:id).pluck(:id)

  Yves Senn

• Do not create useless database transaction when building has_one association.

  Example:

  User.has_one :profile
  User.new.build_profile

  Bogdan Gusiev

• :counter_cache option for has_many associations to support custom named counter caches.
  Fixes #7993.

  Yves Senn

• Deprecate the possibility to pass a string as third argument of add_index.
  Pass unique: true instead.

  add_index(:users, :organization_id, unique: true)

  Rafael Mendonça França

• Raise an ArgumentError when passing an invalid option to add_index.

  Rafael Mendonça França

• Fix find_in_batches crashing when IDs are strings and start option is not specified.

  Alexis Bernard

• AR::Base#attributes_before_type_cast now returns unserialized values for serialized attributes.

  Nikita Afanasenko

• Use query cache/uncache when using DATABASE_URL.
  Fixes #6951.

  kennyj

• Fix bug where update_columns and update_column would not let you update the primary key column.

  Henrik Nyh

• The create_table method raises an ArgumentError when the primary key column is redefined.
  Fixes #6378.

  Yves Senn

• ActiveRecord::AttributeMethods#[] raises ActiveModel::MissingAttributeError
  error if the given attribute is missing. Fixes #5433.

  class Person < ActiveRecord::Base
  belongs_to :company
  end

  # Before:
  person = Person.select(‘id’).first
  person[:name] # => nil
  person.name # => ActiveModel::MissingAttributeError: missing_attribute: name
  person[:company_id] # => nil
  person.company # => nil

  # After:
  person = Person.select(‘id’).first
  person[:name] # => ActiveModel::MissingAttributeError: missing_attribute: name
  person.name # => ActiveModel::MissingAttributeError: missing_attribute: name
  person[:company_id] # => ActiveModel::MissingAttributeError: missing_attribute: company_id
  person.company # => ActiveModel::MissingAttributeError: missing_attribute: company_id

  Francesco Rodriguez

• Small binary fields use the VARBINARY MySQL type, instead of TINYBLOB.

  Victor Costan

• Decode URI encoded attributes on database connection URLs.

  Shawn Veader

• Add find_or_create_by, find_or_create_by! and
  find_or_initialize_by methods to Relation.

  These are similar to the first_or_create family of methods, but
  the behaviour when a record is created is slightly different:

  User.where(first_name: ‘Penélope’).first_or_create

  will execute:

  User.where(first_name: ‘Penélope’).create

  Causing all the create callbacks to execute within the context of
  the scope. This could affect queries that occur within callbacks.

  User.find_or_create_by(first_name: ‘Penélope’)

  will execute:

  User.create(first_name: ‘Penélope’)

  Which obviously does not affect the scoping of queries within
  callbacks.

  The find_or_create_by version also reads better, frankly.

  If you need to add extra attributes during create, you can do one of:

  User.create_with(active: true).find_or_create_by(first_name: ‘Jon’)
  User.find_or_create_by(first_name: ‘Jon’) { |u| u.active = true }

  The first_or_create family of methods have been nodoc'ed in favour
  of this API. They may be deprecated in the future but their
  implementation is very small and it’s probably not worth putting users
  through lots of annoying deprecation warnings.

  Jon Leighton

• Fix bug with presence validation of associations. Would incorrectly add duplicated errors
  when the association was blank. Bug introduced in 1fab518c6a75dac5773654646eb724a59741bc13.

  Scott Willson

• Fix bug where sum(expression) returns string ‘0’ for no matching records.
  Fixes #7439

  Tim Macfarlane

• PostgreSQL adapter correctly fetches default values when using multiple schemas and domains in a db. Fixes #7914

  Arturo Pie

• Learn ActiveRecord::QueryMethods#order work with hash arguments

  When symbol or hash passed we convert it to Arel::Nodes::Ordering.
  If we pass invalid direction(like name: :DeSc) ActiveRecord::QueryMethods#order will raise an exception

  User.order(:name, email: :desc)
  # SELECT “users”.* FROM “users” ORDER BY “users”.“name” ASC, “users”.“email” DESC

  Tima Maslyuchenko

• Rename ActiveRecord::Fixtures class to ActiveRecord::FixtureSet.
  Instances of this class normally hold a collection of fixtures (records)
  loaded either from a single YAML file, or from a file and a folder
  with the same name. This change make the class name singular and makes
  the class easier to distinguish from the modules like
  ActiveRecord::TestFixtures, which operates on multiple fixture sets,
  or DelegatingFixtures, ::Fixtures, etc.,
  and from the class ActiveRecord::Fixture, which corresponds to a single
  fixture.

  Alexey Muranov

• The postgres adapter now supports tables with capital letters.
  Fixes #5920.

  Yves Senn

• CollectionAssociation#count returns 0 without querying if the
  parent record is not persisted.

  Before:

  person.pets.count
  # SELECT COUNT(*) FROM “pets” WHERE “pets”.“person_id” IS NULL
  # => 0

  After:

  person.pets.count
  # fires without sql query
  # => 0

  Francesco Rodriguez

• Fix reset_counters crashing on has_many :through associations.
  Fixes #7822.

  lulalala

• Support for partial inserts.

  When inserting new records, only the fields which have been changed
  from the defaults will actually be included in the INSERT statement.
  The other fields will be populated by the database.

  This is more efficient, and also means that it will be safe to
  remove database columns without getting subsequent errors in running
  app processes (so long as the code in those processes doesn’t
  contain any references to the removed column).

  The partial_updates configuration option is now renamed to
  partial_writes to reflect the fact that it now impacts both inserts
  and updates.

  Jon Leighton

• Allow before and after validations to take an array of lifecycle events

  John Foley

• Support for specifying transaction isolation level

  If your database supports setting the isolation level for a transaction, you can set
  it like so:

  Post.transaction(isolation: :serializable) do
  # …
  end

  Valid isolation levels are:

  • :read_uncommitted
  • :read_committed
  • :repeatable_read
  • :serializable

  You should consult the documentation for your database to understand the
  semantics of these different levels:

  • http://www.postgresql.org/docs/9.1/static/transaction-iso.html
  • https://dev.mysql.com/doc/refman/5.0/en/set-transaction.html

  An ActiveRecord::TransactionIsolationError will be raised if:

  • The adapter does not support setting the isolation level
  • You are joining an existing open transaction
  • You are creating a nested (savepoint) transaction

  The mysql, mysql2 and postgresql adapters support setting the transaction
  isolation level. However, support is disabled for mysql versions below 5,
  because they are affected by a bug (http://bugs.mysql.com/bug.php?id=39170)
  which means the isolation level gets persisted outside the transaction.

  Jon Leighton

• ActiveModel::ForbiddenAttributesProtection is included by default
  in Active Record models. Check the docs of ActiveModel::ForbiddenAttributesProtection
  for more details.

  Guillermo Iguaran

• Remove integration between Active Record and
  ActiveModel::MassAssignmentSecurity, protected_attributes gem
  should be added to use attr_accessible/attr_protected. Mass
  assignment options has been removed from all the AR methods that
  used it (ex. AR::Base.new, AR::Base.create, AR::Base#update_attributes, etc).

  Guillermo Iguaran

• Fix the return of querying with an empty hash.
  Fixes #6971.

  User.where(token: {})

  Before:

  #=> SELECT * FROM users;

  After:

  #=> SELECT * FROM users WHERE 1=0;

  Damien Mathieu

• Fix creation of through association models when using collection=[]
  on a has_many :through association from an unsaved model.
  Fixes #7661.

  Ernie Miller

• Explain only normal CRUD sql (select / update / insert / delete).
  Fix problem that explains unexplainable sql.
  Fixes #7544 #6458.

  kennyj

• You can now override the generated accessor methods for stored attributes
  and reuse the original behavior with read_store_attribute and write_store_attribute,
  which are counterparts to read_attribute and write_attribute.

  Matt Jones

• Accept belongs_to (including polymorphic) association keys in queries.

  The following queries are now equivalent:

  Post.where(author: author)
  Post.where(author_id: author)

  PriceEstimate.where(estimate_of: treasure)
  PriceEstimate.where(estimate_of_type: ‘Treasure’, estimate_of_id: treasure)

  Peter Brown

• Use native mysqldump command instead of structure_dump method
  when dumping the database structure to a sql file. Fixes #5547.

  kennyj

• PostgreSQL inet and cidr types are converted to IPAddr objects.

  Dan McClain

• PostgreSQL array type support. Any datatype can be used to create an
  array column, with full migration and schema dumper support.

  To declare an array column, use the following syntax:

  create_table :table_with_arrays do |t|
  t.integer :int_array, array: true
  # integer[]
  t.integer :int_array, array: true, length: 2
  # smallint[]
  t.string :string_array, array: true, length: 30
  # char varying(30)[]
  end

  This respects any other migration detail (limits, defaults, etc).
  Active Record will serialize and deserialize the array columns on
  their way to and from the database.

  One thing to note: PostgreSQL does not enforce any limits on the
  number of elements, and any array can be multi-dimensional. Any
  array that is multi-dimensional must be rectangular (each sub array
  must have the same number of elements as its siblings).

  If the pg_array_parser gem is available, it will be used when
  parsing PostgreSQL’s array representation.

  Dan McClain

• Attribute predicate methods, such as article.title?, will now raise
  ActiveModel::MissingAttributeError if the attribute being queried for
  truthiness was not read from the database, instead of just returning false.

  Ernie Miller

• ActiveRecord::SchemaDumper uses Ruby 1.9 style hash, which means that the
  schema.rb file will be generated using this new syntax from now on.

  Konstantin Shabanov

• Map interval with precision to string datatype in PostgreSQL. Fixes #7518.

  Yves Senn

• Fix eagerly loading associations without primary keys. Fixes #4976.

  Kelley Reynolds

• Rails now raise an exception when you’re trying to run a migration that has an invalid
  file name. Only lower case letters, numbers, and ‘_’ are allowed in migration’s file name.
  Please see #7419 for more details.

  Jan Bernacki

• Fix bug when calling store_accessor multiple times.
  Fixes #7532.

  Matt Jones

• Fix store attributes that show the changes incorrectly.
  Fixes #7532.

  Matt Jones

• Fix ActiveRecord::Relation#pluck when columns or tables are reserved words.

  Ian Lesperance

• Allow JSON columns to be created in PostgreSQL and properly encoded/decoded.
  to/from database.

  Dickson S. Guedes

• Fix time column type casting for invalid time string values to correctly return nil.

  Adam Meehan

• Allow to pass Symbol or Proc into :limit option of #accepts_nested_attributes_for.

  Mikhail Dieterle

• ActiveRecord::SessionStore has been extracted from Active Record as activerecord-session_store
  gem. Please read the README.md file on the gem for the usage.

  Prem Sichanugrist

• Fix reset_counters when there are multiple belongs_to association with the
  same foreign key and one of them have a counter cache.
  Fixes #5200.

  Dave Desrochers

• serialized_attributes and _attr_readonly become class method only. Instance reader methods are deprecated.

  kennyj

• Round usec when comparing timestamp attributes in the dirty tracking.
  Fixes #6975.

  kennyj

• Use inversed parent for first and last child of has_many association.

  Ravil Bayramgalin

• Fix Column.microseconds and Column.fast_string_to_time to avoid converting
  timestamp seconds to a float, since it occasionally results in inaccuracies
  with microsecond-precision times. Fixes #7352.

  Ari Pollak

• Fix AR#dup to nullify the validation errors in the dup'ed object. Previously the original
  and the dup'ed object shared the same errors.

  Christian Seiler

• Raise ArgumentError if list of attributes to change is empty in update_all.

  Roman Shatsov

• Fix AR#create to return an unsaved record when AR::RecordInvalid is
  raised. Fixes #3217.

  Dave Yeu

• Fixed table name prefix that is generated in engines for namespaced models.

  Wojciech Wnętrzak

• Make sure :environment task is executed before db:schema:load or db:structure:load.
  Fixes #4772.

  Seamus Abshere

• Allow Relation#merge to take a proc.

  This was requested by DHH to allow creating of one’s own custom
  association macros.

  For example:

  module Commentable
  def has_many_comments(extra)
  has_many :comments, -> { where(:foo).merge(extra) }
  end
  end

  class Post < ActiveRecord::Base
  extend Commentable
  has_many_comments -> { where(:bar) }
  end

  Jon Leighton

• Add CollectionProxy#scope.

  This can be used to get a Relation from an association.

  Previously we had a #scoped method, but we’re deprecating that for
  AR::Base, so it doesn’t make sense to have it here.

  This was requested by DHH, to facilitate code like this:

  Project.scope.order(‘created_at DESC’).page(current_page).tagged_with(@tag).limit(5).scoping do
  @topics = @project.topics.scope
  @todolists = @project.todolists.scope
  @attachments = @project.attachments.scope
  @documents = @project.documents.scope
  end

  Jon Leighton

• Add Relation#load.

  This method explicitly loads the records and then returns self.

  Rather than deciding between “do I want an array or a relation?”,
  most people are actually asking themselves “do I want to eager load
  or lazy load?” Therefore, this method provides a way to explicitly
  eager-load without having to switch from a Relation to an array.

  Example:

  @posts = Post.where(published: true).load

  Jon Leighton

• Relation#order: make new order prepend old one.

  User.order(“name asc”).order(“created_at desc”)
  # SELECT * FROM users ORDER BY created_at desc, name asc

  This also affects order defined in default_scope or any kind of associations.

  Bogdan Gusiev

• Model.all now returns an ActiveRecord::Relation, rather than an
  array of records. Use Relation#to_a if you really want an array.

  In some specific cases, this may cause breakage when upgrading.
  However in most cases the ActiveRecord::Relation will just act as a
  lazy-loaded array and there will be no problems.

  Note that calling Model.all with options (e.g.
  Model.all(conditions: '...') was already deprecated, but it will
  still return an array in order to make the transition easier.

  Model.scoped is deprecated in favour of Model.all.

  Relation#all still returns an array, but is deprecated (since it
  would serve no purpose if we made it return a Relation).

  Jon Leighton

• :finder_sql and :counter_sql options on collection associations
  are deprecated. Please transition to using scopes.

  Jon Leighton

• :insert_sql and :delete_sql options on has_and_belongs_to_many
  associations are deprecated. Please transition to using has_many
:through.

  Jon Leighton

• Added #update_columns method which updates the attributes from
  the passed-in hash without calling save, hence skipping validations and
  callbacks. ActiveRecordError will be raised when called on new objects
  or when at least one of the attributes is marked as read only.

  post.attributes # => {“id”=>2, “title”=>“My title”, “body”=>“My content”, “author”=>“Peter”}
  post.update_columns(title: ‘New title’, author: ‘Sebastian’) # => true
  post.attributes # => {“id”=>2, “title”=>“New title”, “body”=>“My content”, “author”=>“Sebastian”}

  Sebastian Martinez + Rafael Mendonça França

• The migration generator now creates a join table with (commented) indexes every time
  the migration name contains the word join_table:

  rails g migration create_join_table_for_artists_and_musics artist_id:index music_id

  Aleksey Magusev

• Add add_reference and remove_reference schema statements. Aliases, add_belongs_to
  and remove_belongs_to are acceptable. References are reversible.

  Examples:

  # Create a user_id column
  add_reference(:products, :user)
  # Create a supplier_id, supplier_type columns and appropriate index
  add_reference(:products, :supplier, polymorphic: true, index: true)
  # Remove polymorphic reference
  remove_reference(:products, :supplier, polymorphic: true)

  Aleksey Magusev

• Add :default and :null options to column_exists?.

  column_exists?(:testings, :taggable_id, :integer, null: false)
  column_exists?(:testings, :taggable_type, :string, default: ‘Photo’)

  Aleksey Magusev

• ActiveRecord::Relation#inspect now makes it clear that you are
  dealing with a Relation object rather than an array:.

  User.where(age: 30).inspect
  # => , #, …]>

  User.where(age: 30).to_a.inspect
  # => [#, #]

  The number of records displayed will be limited to 10.

  Brian Cardarella, Jon Leighton & Damien Mathieu

• Add collation and ctype support to PostgreSQL. These are available for PostgreSQL 8.4 or later.
  Example:

  development:
  adapter: postgresql
  host: localhost
  database: rails_development
  username: foo
  password: bar
  encoding: UTF8
  collation: ja_JP.UTF8
  ctype: ja_JP.UTF8

  kennyj

• Changed validates_presence_of on an association so that children objects
  do not validate as being present if they are marked for destruction. This
  prevents you from saving the parent successfully and thus putting the parent
  in an invalid state.

  Nick Monje & Brent Wheeldon

• FinderMethods#exists? now returns false with the false argument.

  Egor Lynko

• Added support for specifying the precision of a timestamp in the PostgreSQL
  adapter. So, instead of having to incorrectly specify the precision using the
  :limit option, you may use :precision, as intended. For example, in a migration:

  def change
  create_table :foobars do |t|
  t.timestamps precision: 0
  end
  end

  Tony Schneider

• Allow ActiveRecord::Relation#pluck to accept multiple columns. Returns an
  array of arrays containing the typecasted values:

  Person.pluck(:id, :name)
  # SELECT people.id, people.name FROM people
  # [[1, ‘David’], [2, ‘Jeremy’], [3, ‘Jose’]]

  Jeroen van Ingen & Carlos Antonio da Silva

• Improve the derivation of HABTM join table name to take account of nesting.
  It now takes the table names of the two models, sorts them lexically and
  then joins them, stripping any common prefix from the second table name.

  Some examples:

  Top level models (Category <=> Product)
  Old: categories_products
  New: categories_products

  Top level models with a global table_name_prefix (Category <=> Product)
  Old: site_categories_products
  New: site_categories_products

  Nested models in a module without a table_name_prefix method (Admin::Category <=> Admin::Product)
  Old: categories_products
  New: categories_products

  Nested models in a module with a table_name_prefix method (Admin::Category <=> Admin::Product)
  Old: categories_products
  New: admin_categories_products

  Nested models in a parent model (Catalog::Category <=> Catalog::Product)
  Old: categories_products
  New: catalog_categories_products

  Nested models in different parent models (Catalog::Category <=> Content::Page)
  Old: categories_pages
  New: catalog_categories_content_pages

  Andrew White

• Move HABTM validity checks to ActiveRecord::Reflection. One side effect of
  this is to move when the exceptions are raised from the point of declaration
  to when the association is built. This is consistent with other association
  validity checks.

  Andrew White

• Added stored_attributes hash which contains the attributes stored using
  ActiveRecord::Store. This allows you to retrieve the list of attributes
  you’ve defined.

  class User < ActiveRecord::Base
  store :settings, accessors: [:color, :homepage]
  end

  User.stored_attributes[:settings] # [:color, :homepage]

  Joost Baaij & Carlos Antonio da Silva

• PostgreSQL default log level is now ‘warning’, to bypass the noisy notice
  messages. You can change the log level using the min_messages option
  available in your config/database.yml.

  kennyj

• Add uuid datatype support to PostgreSQL adapter.

  Konstantin Shabanov

• Added ActiveRecord::Migration.check_pending! that raises an error if
  migrations are pending.

  Richard Schneeman

• Added #destroy! which acts like #destroy but will raise an
  ActiveRecord::RecordNotDestroyed exception instead of returning false.

  Marc-André Lafortune

• Added support to CollectionAssociation#delete for passing fixnum
  or string values as record ids. This finds the records responding
  to the id and executes delete on them.

  class Person < ActiveRecord::Base
  has_many :pets
  end

  person.pets.delete(“1”) # => [#]
  person.pets.delete(2, 3) # => [#, #]

  Francesco Rodriguez

• Deprecated most of the ‘dynamic finder’ methods. All dynamic methods
  except for find_by_... and find_by_...! are deprecated. Here’s
  how you can rewrite the code:

  • find_all_by_... can be rewritten using where(...)
  • find_last_by_... can be rewritten using where(...).last
  • scoped_by_... can be rewritten using where(...)
  • find_or_initialize_by_... can be rewritten using where(...).first_or_initialize
  • find_or_create_by_... can be rewritten using find_or_create_by(...) or where(…).first_or_create`
  • find_or_create_by_...! can be rewritten using find_or_create_by!(...) orwhere(…).first_or_create!`

  The implementation of the deprecated dynamic finders has been moved
  to the activerecord-deprecated_finders gem. See below for details.

  Jon Leighton

• Deprecated the old-style hash based finder API. This means that
  methods which previously accepted “finder options” no longer do. For
  example this:

  Post.find(:all, conditions: { comments_count: 10 }, limit: 5)

  Should be rewritten in the new style which has existed since Rails 3:

  Post.where(comments_count: 10).limit(5)

  Note that as an interim step, it is possible to rewrite the above as:

  Post.all.merge(where: { comments_count: 10 }, limit: 5)

  This could save you a lot of work if there is a lot of old-style
  finder usage in your application.

  Relation#merge now accepts a hash of
  options, but they must be identical to the names of the equivalent
  finder method. These are mostly identical to the old-style finder
  option names, except in the following cases:

  • :conditions becomes :where.
  • :include becomes :includes.

  The code to implement the deprecated features has been moved out to the
  activerecord-deprecated_finders gem. This gem is a dependency of Active
  Record in Rails 4.0, so the interface works out of the box. It will no
  longer be a dependency from Rails 4.1 (you’ll need to add it to the
  Gemfile in 4.1), and will be maintained until Rails 5.0.

  Jon Leighton

• It’s not possible anymore to destroy a model marked as read only.

  Johannes Barre

• Added ability to ActiveRecord::Relation#from to accept other ActiveRecord::Relation objects.

  Record.from(subquery)
  Record.from(subquery, :a)

  Radoslav Stankov

• Added custom coders support for ActiveRecord::Store. Now you can set
  your custom coder like this:

  store :settings, accessors: [ :color, :homepage ], coder: JSON

  Andrey Voronkov

• mysql and mysql2 connections will set SQL_MODE=STRICT_ALL_TABLES by
  default to avoid silent data loss. This can be disabled by specifying
  strict: false in your database.yml.

  Michael Pearson

• Added default order to first to assure consistent results among
  different database engines. Introduced take as a replacement to
  the old behavior of first.

  Marcelo Silveira

• Added an :index option to automatically create indexes for references
  and belongs_to statements in migrations.

  The references and belongs_to methods now support an index
  option that receives either a boolean value or an options hash
  that is identical to options available to the add_index method:

  create_table :messages do |t|
  t.references :person, index: true
  end

  Is the same as:

  create_table :messages do |t|
  t.references :person
  end
  add_index :messages, :person_id

  Generators have also been updated to use the new syntax.

  Joshua Wood

• Added #find_by and #find_by! to mirror the functionality
  provided by dynamic finders in a way that allows dynamic input more
  easily:

  Post.find_by name: ‘Spartacus’, rating: 4
  Post.find_by “published_at < ?”, 2.weeks.ago
  Post.find_by! name: ‘Spartacus’

  Jon Leighton

• Added ActiveRecord::Base#slice to return a hash of the given methods with
  their names as keys and returned values as values.

  Guillermo Iguaran

• Deprecate eager-evaluated scopes.

  Don’t use this:

  scope :red, where(color: ‘red’)
  default_scope where(color: ‘red’)

  Use this:

  scope :red, -> { where(color: ‘red’) }
  default_scope { where(color: ‘red’) }

  The former has numerous issues. It is a common newbie gotcha to do
  the following:

  scope :recent, where(published_at: Time.now - 2.weeks)

  Or a more subtle variant:

  scope :recent, -> { where(published_at: Time.now - 2.weeks) }
  scope :recent_red, recent.where(color: ‘red’)

  Eager scopes are also very complex to implement within Active
  Record, and there are still bugs. For example, the following does
  not do what you expect:

  scope :remove_conditions, except(:where)
  where(…).remove_conditions # => still has conditions

  Jon Leighton

• Remove IdentityMap

  IdentityMap has never graduated to be an “enabled-by-default” feature, due
  to some inconsistencies with associations, as described in this commit:

  https://github.com/rails/rails/commit/302c912bf6bcd0fa200d964ec2dc4a44abe328a6

  Hence the removal from the codebase, until such issues are fixed.

  Carlos Antonio da Silva

• Added the schema cache dump feature.

  Schema cache dump feature was implemented. This feature can dump/load internal state of SchemaCache instance
  because we want to boot rails more quickly when we have many models.

  Usage notes:

  1) execute rake task.
  RAILS_ENV=production bundle exec rake db:schema:cache:dump
  => generate db/schema_cache.dump

  2) add config.active_record.use_schema_cache_dump = true in config/production.rb. BTW, true is default.

  3) boot rails.
  RAILS_ENV=production bundle exec rails server
  => use db/schema_cache.dump

  4) If you remove clear dumped cache, execute rake task.
  RAILS_ENV=production bundle exec rake db:schema:cache:clear
  => remove db/schema_cache.dump

  kennyj

• Added support for partial indices to PostgreSQL adapter.

  The add_index method now supports a where option that receives a
  string with the partial index criteria.

  add_index(:accounts, :code, where: ‘active’)

  generates

  CREATE INDEX index_accounts_on_code ON accounts(code) WHERE active

  Marcelo Silveira

• Implemented ActiveRecord::Relation#none method.

  The none method returns a chainable relation with zero records
  (an instance of the NullRelation class).

  Any subsequent condition chained to the returned relation will continue
  generating an empty relation and will not fire any query to the database.

  Juanjo Bazán

• Added the ActiveRecord::NullRelation class implementing the null
  object pattern for the Relation class.

  Juanjo Bazán

• Added new dependent: :restrict_with_error option. This will add
  an error to the model, rather than raising an exception.

  The :restrict option is renamed to :restrict_with_exception to
  make this distinction explicit.

  Manoj Kumar & Jon Leighton

• Added create_join_table migration helper to create HABTM join tables.

  create_join_table :products, :categories
  # =>
  # create_table :categories_products, id: false do |td|
  # td.integer :product_id, null: false
  # td.integer :category_id, null: false
  # end

  Rafael Mendonça França

• The primary key is always initialized in the @attributes hash to nil (unless
  another value has been specified).

  Aaron Patterson

• In previous releases, the following would generate a single query with
  an OUTER JOIN comments, rather than two separate queries:

  Post.includes(:comments)
  .where(“comments.name = ‘foo’”)

  This behaviour relies on matching SQL string, which is an inherently
  flawed idea unless we write an SQL parser, which we do not wish to
  do.

  Therefore, it is now deprecated.

  To avoid deprecation warnings and for future compatibility, you must
  explicitly state which tables you reference, when using SQL snippets:

  Post.includes(:comments)
  .where(“comments.name = ‘foo’”)
  .references(:comments)

  Note that you do not need to explicitly specify references in the
  following cases, as they can be automatically inferred:

  Post.includes(:comments).where(comments: { name: ‘foo’ })
  Post.includes(:comments).where(‘comments.name’ => ‘foo’)
  Post.includes(:comments).order(‘comments.name’)

  You do not need to worry about this unless you are doing eager
  loading. Basically, don’t worry unless you see a deprecation warning
  or (in future releases) an SQL error due to a missing JOIN.

  Jon Leighton

• Support for the schema_info table has been dropped. Please
  switch to schema_migrations.

  Aaron Patterson

• Connections must be closed at the end of a thread. If not, your
  connection pool can fill and an exception will be raised.

  Aaron Patterson

• PostgreSQL hstore records can be created.

  Aaron Patterson

• PostgreSQL hstore types are automatically deserialized from the database.

  Aaron Patterson

Please check 3-2-stable for previous changes.