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

See the CHANGELOG for details.

Fixes #950.

This is to avoid confusing newbies, and to be consistent with the fact
that other options like :foreign_key already allow a symbol or a string.

Building the conditions of a nested through association could
potentially modify the conditions of the through and/or source
association.

This is a Bad Thing.

An association between two models cannot be made if a relevant key is
unknown, so fail fast rather than generating invalid SQL. Fixes #3207.

Closes #3104.

Refactor Active Record test connection setup. Please see the RUNNING_UNIT_TESTS file for details, but essentially you can now configure things in test/config.yml. You can also run tests directly via the command line, e.g. ruby path/to/test.rb (no rake needed, uses default db connection from test/config.yml). This will help us fix the CI by enabling us to isolate the different Rails versions to different databases.

Fix problem with loading polymorphic associations which have been defined in an abstract superclass. Fixes #552.

Rename Reflection#through_reflection_chain and #through_options to Reflection#chain and Reflection#options as they now no longer relate solely to through associations.

Push source_type and polymorphic conditions out of ThroughAssociation and JoinDependency::JoinAssociation and into the reflection instead.

Construct an actual ActiveRecord::Relation object for the association scope, rather than a hash which is passed to apply_finder_options. This allows more flexibility in how the scope is created, for example because scope.where(a, b) and scope.where(a).where(b) mean different things.

Implement deprecated version of AssociationReflection#primary_key_name, which has been renamed to #foreign_key. Also bumping the deprecation_horizon in Active Support to 3.1.

Rename AssociationReflection#primary_key_name to foreign_key, since the options key which it relates to is :foreign_key

Improved strategy for updating a belongs_to association when the foreign key changes. Rather than resetting each affected association when the foreign key changes, we should lazily check for 'staleness' (where fk does not match target id) when the association is accessed.

Fix problem where wrong keys are used in JoinAssociation when an association goes :through a belongs_to [#2801 state:resolved]

[#4945 state:resolved]
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Signed-off-by: Nwycats <wycats@gmail.com>