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.

It's not really a good idea to have this as a global config option. We
should allow people to specify the behaviour per association.

There will now be two new values:

* :dependent => :restrict_with_exception implements the current
  behaviour of :restrict. :restrict itself is deprecated in favour of
  :restrict_with_exception.
* :dependent => :restrict_with_error implements the new behaviour - it
  adds an error to the owner if there are dependent records present

See #4727 for the original discussion of this.

It doesn't serve much purpose now that ActiveRecord::Base.all returns a
Relation.

The code is moved to active_record_deprecated_finders.

Previously it returned an Array.

If you want an array, call e.g. `Post.to_a` rather than `Post.all`. This
is more explicit.

In most cases this should not break existing code, since
Relations use method_missing to delegate unknown methods to #to_a
anyway.

Assign the association attributes to the associated record before the before_initialize callback of the record runs. Fixes #1842.

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.

The build_association method was added as an API for plugins
to hook into in 1398db01. This commit restores this API and the
ability to override class.new to return a subclass based on
a virtual attribute in the attributes hash.

Don't use mass-assignment protection when setting foreign keys or association conditions on singular associations. Fixes #481 (again).

Deprecated support for passing hashes and relations to default_scope, in favour of defining a 'default_scope' class method in the model. See the CHANGELOG for more details.

Split AssociationProxy into an Association class (and subclasses) which manages the association, and a CollectionProxy class which is *only* a proxy. Singular associations no longer have a proxy. See CHANGELOG for more.

Add interpolation of association conditions back in, in the form of proc { ... } rather than instance_eval-ing strings

We shouldn't be using scoped.scoping { ... } to build associated records, as this can affect validations/callbacks/etc inside the record itself [#6252 state:resolved]

When assigning a has_one, if the existing record fails to be removed from the association, raise an error