Rails 4.0.0 (unreleased)

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 revertible). 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. Fix #8575.

Rafael Mendonça França
Keep index names when using alter_table with sqlite3. Fix #3489.

Yves Senn
Add ability for postgresql adapter to disable user triggers in disable_referential_integrity. Fix #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'. Fix #8492

Yves Senn
Add ActiveRecord::Base.cache_timestamp_format class attribute to control the format of the timestamp value in the cache key. This allows users to improve the precision of the cache key. Fixes #8195.

Rafael Mendonça França
Add :nsec date format. This can be used to improve the precision of cache key.

Jamie Gaskins
Session variables can be set for the mysql, mysql2, and postgresql adapters in the variables: <hash> parameter in 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 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. Fix #8414

kennyj
Do not instantiate intermediate Active Record objects when eager loading. These records caused after_find to run more than expected. Fix #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. Fix #8310

Alisdair McDiarmid
Prevent mass assignment to the type column of polymorphic associations when using build Fix #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. Fix #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. Fix #6951.

kennyj
Added #none! method for mutating ActiveRecord::Relation objects to a NullRelation. It acts like #none but modifies relation in place.

Juanjo Bazán
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. Fix #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. Fix #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. Fix #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. Fix #6971.

User.where(token: {})

Before:

#=> SELECT * FROM users;

After:

#=> SELECT * FROM users WHERE 1 = 2;

Damien Mathieu

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

Ernie Miller
Explain only normal CRUD sql (select / update / insert / delete). Fix problem that explains unexplainable sql. Closes #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 consistant 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.
- :extend becomes :extending.
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. It will no longer be a dependency from Rails 4.1, but if your app relies on the deprecated features then you can add it to your own Gemfile. It will be maintained by the Rails core team until Rails 5.0 is released.

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 bang methods for mutating ActiveRecord::Relation objects. For example, while foo.where(:bar) will return a new object leaving foo unchanged, foo.where!(:bar) will mutate the foo object

Jon Leighton
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 implemetend. 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 Paterson
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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Rails 4.0.0 (unreleased)

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Rails 4.0.0 (unreleased)