unreleased

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Before this change, the default scope from Post was not applied, so we'd get comments on unpublished posts.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

Remove column restrictions for count, let the database raise if the SQL is invalid. The previos behavior was untested and surprising for the user. Fixes #5554.

Example:

User.select("name, username").count
# Before => SELECT count(*) FROM users
# After => ActiveRecord::StatementInvalid

# you can still use `count(:all)` to perform a query unrelated to the
# selected columns
User.select("name, username").count(:all) # => SELECT count(*) FROM users

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=>[#<Arel::Nodes::Equality: ....}. In this relation all the context that Post was joined with Author is lost and hence the error that author was not found on Comment.

The solution is to build JoinAssociation when two relations with join information are being merged. And later while building the Arel use the previously built JoinAssociation record in JoinDependency#graft to build the right from clause. Fixes #3002.

Jared Armstrong and Neeraj Singh
default_scopes? is deprecated. Check for default_scopes.empty? instead.

Agis Anastasopoulos
Default values for PostgreSQL bigint types now get parsed and dumped to the schema correctly.

Erik Peterson
Fix associations with :inverse_of option when building association with a block. Inside the block the parent object was different then after the block.

Example:
```
parent.association.build do |child|
  child.parent.equal?(parent) # false
end

# vs

child = parent.association.build
child.parent.equal?(parent) # true
```
Michal Cichra
has_many using :through now obeys the order clause mentioned in through association. Fixes #10016.

Neeraj Singh

belongs_to :touch behavior now touches old association when transitioning to new association.

class Passenger < ActiveRecord::Base
  belongs_to :car, touch: true
end

car_1 = Car.create
car_2 = Car.create

passenger = Passenger.create car: car_1

passenger.car = car_2
passenger.save

Previously only car_2 would be touched. Now both car_1 and car_2 will be touched.

Adam Gamble

Extract and deprecate Firebird / Sqlserver / Oracle database tasks, because These tasks should be supported by 3rd-party adapter.

kennyj
Allow ActiveRecord::Base.connection_handler to have thread affinity and be settable, this effectively allows Active Record to be used in a multithreaded setup with multiple connections to multiple databases.

Sam Saffron
rename_column preserves auto_increment in MySQL migrations. Fixes #3493.

Vipul A M
PostgreSQL geometric type point is now supported by Active Record. Fixes #7324.

Martin Schuerrer
Add support for concurrent indexing in PostgreSQL adapter via the algorithm: :concurrently option.
```
add_index(:people, :last_name, algorithm: :concurrently)
```
Also add support for MySQL index algorithms (COPY, INPLACE, DEFAULT) via the :algorithm option.
```
add_index(:people, :last_name, algorithm: :copy) # or :inplace/:default
```
Dan McClain
Add support for fulltext and spatial indexes on MySQL tables with MyISAM database engine via the type: 'FULLTEXT' / type: 'SPATIAL' option.
```
add_index(:people, :last_name, type: 'FULLTEXT')
add_index(:people, :last_name, type: 'SPATIAL')
```
Ken Mazaika
Add an add_index override in PostgreSQL adapter and MySQL adapter to allow custom index type support. Fixes #6101.
```
add_index(:wikis, :body, :using => '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: <hash> 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
# => <ActiveRecord::Relation [#<User ...>, #<User ...>, ...]>

User.where(age: 30).to_a.inspect
# => [#<User ...>, #<User ...>]
```
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") # => [#<Pet id: 1>]
person.pets.delete(2, 3) # => [#<Pet id: 2>, #<Pet id: 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!(...) or where(...).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.

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CHANGELOG.md

CHANGELOG.md

unreleased

Rails 4.0.0 (June 25, 2013)

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unreleased

Rails 4.0.0 (June 25, 2013)