Previously `has_one` and `has_many` associations were using the
`one` and `many` keys respectively. Both of these keys have special
meaning in I18n (they are considered to be pluralizations) so by
renaming them to `has_one` and `has_many` we make the messages more
explicit and most importantly they don't clash with linguistical
systems that need to validate translation keys (and their
pluralizations).

The `:'restrict_dependent_destroy.one'` key should be replaced with
`:'restrict_dependent_destroy.has_one'`, and
`:'restrict_dependent_destroy.many'` with
`:'restrict_dependent_destroy.has_many'`.

[Roque Pinel & Christopher Dell]

We deprecate the support for passing an argument to force reload in
6eae366d. That led to several
deprecation warning when running Active Record test suite.

This commit silence the warnings by properly calling `#reload` on the
association proxy or on the association object instead. However, there
are several places that `ActiveSupport::Deprecation.silence` are used as
those tests actually tests the force reload functionality and will be
removed once `master` is targeted next minor release (5.1).

This is to simplify the association API, as you can call `reload` on the
association proxy or the parent object to get the same result.

For collection association, you can call `#reload` on association proxy
to force a reload:

    @user.posts.reload   # Instead of @user.posts(true)

For singular association, you can call `#reload` on the parent object to
clear its association cache then call the association method:

    @user.reload.profile   # Instead of @user.profile(true)

Passing a truthy argument to force association to reload will be removed
in Rails 5.1.

The changes introduced to through associations in c80487eb were quite
interesting. Changing `relation.merge!(scope)` to `relation =
relation.merge(scope)` should in theory never cause any changes in
behavior. The subtle breakage led to a surprising conclusion.

The old code wasn't doing anything! Since `merge!` calls
`instance_exec` when given a proc, and most scopes will look something
like `has_many :foos, -> { where(foo: :bar) }`, if we're not capturing
the return value, it's a no-op. However, removing the `merge` causes
`unscope` to break.

While we're merging in the rest of the chain elsewhere, we were never
merging in `unscope` values, causing a breakage on associations where a
default scope was being unscoped in an association scope (yuk!). This is
subtly related to #20722, since it appears we were previously relying on
this mutability.

Fixes #20721.
Fixes #20727.

thrown ActiveRecord::AssociationTypeMismatch when assigning a wrong value for a namespaced association

fixes #20541

raise ActiveModel::MissingAttributeError when trying to access a relationship without the foreign key attribute

fixes regression reported on #20253

ActiveRecord::Base#[] was not used cause of 8b954200

Unitialized polymorphic `belongs_to` associations raise an error while
attempting to reload, as they attempt to make an uncached reload, but
don't have a klass to fetch uncachedly. In this case, `loaded?` should
be `false` anyway.

See #9683 for the reasons we switched to `distinct`.

Here is the discussion that triggered the actual deprecation #20198.

`uniq`, `uniq!` and `uniq_value` are still around.
They will be removed in the next minor release after Rails 5.

The old `test_create_bang_returns_falsy_when_join_record_has_errors` had
a missleading name and was a duplicate of
`test_save_should_not_raise_exception_when_join_record_has_errors`.

Since it had an assertion on the return value I renamed it accordingly
and got rid of the duplicate test.

When `AR::Base.save!` or `AR::Base.destroy!` is called and an exception
is raised, the exception doesn't have any error message or has a weird
message like `#<FailedBulb:0x0000000907b4b8>`. Give a better message so
we can easily understand why it's failing to save/destroy.

In 1f006c an option was added called :class to allow passing anonymous
classes to association definitions. Since using :class instead of
:class_name is a fairly common typo even amongst experienced developers
this can result in hard to debug errors arising in raise_on_type_mismatch?

To fix this we're renaming the option from :class to :anonymous_class as
that is a more correct description of what the option is for. Since this
was an internal, undocumented option there is no need for a deprecation.

Fixes #19659

[fixes #18606]

Make belongs_to use touch over touch_later when running the callbacks.

Add more tests and small method rename

Thanks Jeremy for the feedback.

When replacing a has_many association with the same one, there is nothing to do with database but a setter method should still return the substituted value for backward compatibility.

- Eager loading was not working for the default_scope (class method)
  for 'find' & 'find_by' methods.
- Fixed these by adding a new check 'respond_to?(:default_scope)'.

I’m renaming all instances of `use_transcational_fixtures` to
`use_transactional_tests` and “transactional fixtures” to
“transactional tests”.

I’m deprecating `use_transactional_fixtures=`. So anyone who is
explicitly setting this will get a warning telling them to use
`use_transactional_tests=` instead.

I’m maintaining backwards compatibility—both forms will work.
`use_transactional_tests` will check to see if
`use_transactional_fixtures` is set and use that, otherwise it will use
itself. But because `use_transactional_tests` is a class attribute
(created with `class_attribute`) this requires a little bit of hoop
jumping. The writer method that `class_attribute` generates defines a
new reader method that return the value being set. Which means we can’t
set the default of `true` using `use_transactional_tests=` as was done
previously because that won’t take into account anyone using
`use_transactional_fixtures`. Instead I defined the reader method
manually and it checks `use_transactional_fixtures`. If it was set then
it should be used, otherwise it should return the default, which is
`true`. If someone uses `use_transactional_tests=` then it will
overwrite the backwards-compatible method with whatever they set.

When a new record has the necessary information prior to save, we can
avoid busting the cache.

We could simply clear the @proxy on #reset or #reset_scope, but that
would clear the cache more often than necessary.

This reverts commit ff18049c.

This broke the AR build for every adapter:

      1) Error:
    AssociationCallbacksTest#test_dont_add_if_before_callback_raises_exception:
    Exception: You can't add a post

      2) Failure:
    QueryCacheTest#test_query_cache_doesnt_leak_cached_results_of_rolled_back_queries [/Users/senny/Projects/rails/activerecord/test/cases/query_cache_test.rb:235]:
    Expected: 1
      Actual: 0

I'm reverting to get the build green again.

Various behaviors needed by associations (such as creating the through
record) are lost when `where` is called, since we stop having a
`CollectionProxy` and start having an `AssociationRelation` which does
not contain this behavior. I *think* we should be able to rm
`AssociationRelation`, but we have tests saying the changes required to
do that would be bad (Without saying why. Of course. >_>)

Fixes #19073.

The name `ActiveModel::AttributeAssignment::UnknownAttributeError` is
too implementation specific so let's move the constant directly under
the ActiveModel namespace.

Also since this constant used to be under the ActiveRecord namespace, to
make the upgrade path easier, let's avoid raising the former constant
when we deal with this error on the Active Record side.

Deprecate `required` option in favor of `optional` for belongs_to.

Use SQL COUNT and LIMIT 1 queries for none? and one? methods if no block or limit is given,
instead of loading the entire collection to memory. The any? and many? methods already
follow this behavior.

[Eugene Gilburg & Rafael Mendonça França]

Fixes #18696.

The column is primarily used for type casting, which we're trying to
separate from the idea of a column. Since what we really need is the
combination of a name, type, and value, let's use the object that we
already have to represent that concept, rather than this tuple. No
consumers of the bind values have been changed, only the producers
(outside of tests which care too much about internals). This is
*finally* possible since the bind values are now produced from a
reasonable number of lcoations.

The only place it was accessed was in tests. Many of them have another
way that they can test their behavior, that doesn't involve reaching
into internals as far as they did. `AssociationScopeTest` is testing a
situation where the where clause would have one bind param per
predicate, so it can just ignore the predicates entirely. The where
chain test was primarly duplicating the logic tested on `WhereClause`
directly, so I instead just make sure it calls the appropriate method
which is fully tested in isolation.

Allows to use it for any object as an includable module.

after_commit callbacks run after committing a transaction whose parent
is not `joinable?`: un-nested transactions, transactions within test
cases, and transactions in `console --sandbox`.

Addresses https://github.com/rails/rails/commit/ed56e596a0467390011bc9d56d462539776adac1#commitcomment-9145960

This error only happens when the foreign key is missing.

Before this fix the following exception was being raised:

    NoMethodError: undefined method `val' for #<Arel::Nodes::BindParam:0x007fc64d19c218>

Now the message is:

    ActiveRecord::UnknownAttributeError: unknown attribute 'foreign_key' for Model.