This revision makes crystal clear that the methods go
straight to the database and update the receiver. It
also adds and example, and removes the duplication
in the singular and plural forms by referring one to
the other.

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.

Move instantiation responsibilities from Inheritance to Persistence. Have Inheritance#discriminate_class_for_record handle STI lookup duties.

They was extracted from a plugin.

See https://github.com/rails/rails-observers

[Rafael Mendonça França + Steve Klabnik]

If you want to change the STI type too, use AR::Base.becomes! instead

Didn't work before because it updated the model-in-memory first, so the DB query couldn't find the record.

Another batch of hash syntax changes to comment, this time around, I tried to keep 'output' messages untouched.

- Changed the comments documentation for the update_column(s) methods to add a little bit of clarity

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).

Update AR::Base.create and AR:Base#update_attributes docs to remove references to mass assignment options

I had to create a new table because I needed an STI table,
which does not have both a "type" and a "custom_type"

the test fails with:
  1) Error:
test_alt_becomes_works_with_sti(InheritanceTest):
NoMethodError: undefined method `type=' for #<Cabbage id: 1, name: "my cucumber", custom_type: "Cucumber">
    /Users/username/Projects/rails/activemodel/lib/active_model/attribute_methods.rb:432:in `method_missing'
    /Users/username/Projects/rails/activerecord/lib/active_record/attribute_methods.rb:100:in `method_missing'
    /Users/username/Projects/rails/activerecord/lib/active_record/persistence.rb:165:in `becomes'
    test/cases/inheritance_test.rb:134:in `test_becomes_works_with_sti'
    test/cases/inheritance_test.rb:140:in `test_alt_becomes_works_with_sti'

This reverts commit 7a8aee08.

This reverts commit a7f4b0a1.

Conflicts:
	activerecord/lib/active_record/associations/has_one_association.rb
	activerecord/lib/active_record/persistence.rb
	activerecord/test/cases/base_test.rb
	activerecord/test/cases/dirty_test.rb
	activerecord/test/cases/timestamp_test.rb

This method was added to be shared between update_attribute and
update_column in 50725cec, but since
update_attribute was removed, and update_column has changed to delegate
to update_columns, the method is not used anywhere anymore.

Also remove "key.to_s" conversion when raising readonly error, since
the key is being interpolated.

update_column was suggested as replacement of update_attribute at the
last release of 3-2-stable, so deprecating it now will confuse the
users.

This reverts commit 14fc8b34.

Reason: we need to discuss a better path from this removal.

Conflicts:
	activerecord/lib/active_record/reflection.rb
	activerecord/test/cases/base_test.rb
	activerecord/test/models/developer.rb

Closes #1190

This feature adds a lot of complication to ActiveRecord for dubious
value. Let's talk about what it does currently:

class Customer < ActiveRecord::Base
  composed_of :balance, :class_name => "Money", :mapping => %w(balance amount)
end

Instead, you can do something like this:

    def balance
      @balance ||= Money.new(value, currency)
    end

    def balance=(balance)
      self[:value] = balance.value
      self[:currency] = balance.currency
      @balance = balance
    end

Since that's fairly easy code to write, and doesn't need anything
extra from the framework, if you use composed_of today, you'll
have to add accessors/mutators like that.

Closes #1436
Closes #2084
Closes #3807

Historically, update_attribute and update_attributes are similar, but
with one big difference: update_attribute does not run validations.
These two methods are really easy to confuse given their similar
names. Therefore, update_attribute is being removed in favor of
update_column.

See the thread on rails-core here:
https://groups.google.com/forum/?fromgroups#!topic/rubyonrails-core/BWPUTK7WvYA

This reverts commit fa6d921e.

Reason: Not a fan of such massive changes. We usually close such changes
if made to Rails master as a pull request. Following the same principle
here and reverting.

[ci skip]

For future reference, this is the regex I used: ^\s*#\s*\n(?!\s*#). Replace
with the first match, and voilà! Note that the regex matches a little bit too
much, so you probably want to `git add -i .` and go through every single diff
to check if it actually should be changed.

Cleaned up "DEPRECATION WARNING: Passing options to #find is
deprecated. Please build a scope and then call #find on it."