Since 07e5301e, `Relation#first` will order by primary key if no order is
defined.

Fixes #28324.

It is covered by following assertion.

This reverts commit 3420a145, reversing
changes made to afb66a5a.

Fixes #29627.

`aliased_table_name` in `Association` was added at a3502c41.
`aliased_table_name` in `JoinDependency` (added at 55854c41) is used, but
it looks like that added one in `Association` is never used from the
beginning.

Passing `klass.connection` is redundant because `AssociationScope` is
passed an association itself and an association has `klass`.

Unscoping `default_scope` in associations has already supported (#17360
for preloading, c9cf8b8d for eager loading).

Fixes #20679.
Closes #16531.

And use `assert_same` instead of `assert_equal` and tiny fix assert
message s/#reload/#reset/.

Follow up of #29511.

If a record was built on a HasManyThroughAssociation, then removed, and
then the record was saved, the removed record would be created anyways.

The `@offsets` cache is used by FinderMethods to cache records found by
find_nth. This cache is cleared in AR::Relation#reset, but not in
CollectionProxy#reset or CollectionProxy#reload.

Because of this, since #29098, calling #first/#find_nth/etc after
calling #reload or #reset on an association could return a stale record.
This is an issue both when the full association target is loaded and
when the item is loaded in #find_nth.

This commit solves the problem by clearing the `@offsets` cache in
CollectionProxy#reset and CollectionProxy#reload.

A collection association will raise on `#create_association` when the parent is
unpersisted. A singular association should do the same. This addresses
issue #29219.

These `assert_nothing_raised` are covered by following assertions.

This fixes the following issues.

* `association_scope` doesn't include `default_scope`. Should use `scope` instead.
* We can't use `method_missing` for customizing existing method.
* We can't use `relation_delegate_class` for sharing extensions. Should extend per association.

".. with __dir__ we can restore order in the Universe." - by @fxn

Related to 5b8738c2

`make_model` and `make_no_pk_hm_t` in `HasManyThroughAssociationsTest`
are not a test case. it should be private.

Fixes #29025.

This change reverted in eac6f369 but it is needed for data integrity.
See #25328.

Revert "Merge pull request #27636 from mtsmfm/disable-referential-integrity-without-superuser-privilege-take-2"

This reverts commit c1faca63, reversing
changes made to 8c658a0e.

See https://github.com/rails/rails/pull/27636#issuecomment-297534129

Cannot call private methods in `@klass` against `CollectionProxy`
(inherites `Relation`) because using `public_send` in `method_missing`.

Follow up of 03d3f036.

Some of `respond_to?` were replaced to `respond_to_missing?` in 03d3f036.
But the visibility is still public. It should be private.

Fixes #24032

Prevent double firing the before save callback of new object when the parent association saved in the callback

Related #18155, #26661, 268a5bb0, #27434, #27442, and #28599.

Originally #18155 was introduced for preventing double insertion caused
by the after save callback. But it was caused the before save issue
(#26661). 268a5bb0 fixed #26661, but it was caused the performance
regression (#27434). #27442 added new record to `target` before calling
callbacks for fixing #27434. But it was caused double firing before save
callback (#28599). We cannot add new object to `target` before saving
the object.

This is improving #18155 to only track callbacks after `save`.

Fixes #28599.

Add regression test for setting inverse instances on normal & polymorphic relationships when building objects on new records

This makes automatic inverse detection possible for polymorphic
:has_one & :has_many possible.

This resolves a number of issues, eg. `touch: true` on polymorphic relationships (#16446) and automatically setting inverse associations on newly built objects (#15028, #21843).

Re-create https://github.com/rails/rails/pull/21233

eeac6151 was reverted (127509c0) because it breaks tests.

----------------

ref: 72c15572

- We must use `authors` fixture with `author_addresses` because of its foreign key constraint.
- Tests require PostgreSQL >= 9.4.2 because it had a bug about `ALTER CONSTRAINTS` and fixed in 9.4.2.

Extension methods should not delegate to `scope` to respect dirty
target on `CollectionProxy`.

Fixes #28419.

Since b644964b `ActiveRecord::Relation` includes `Enumerable` so
delegating `collect`, `all?`, and `include?` are also unneeded.
`collect` without block returns `Enumerable` without preloading by that.
We should use `load` rather than `collect` for force loading.

Use it to specify that an association should be initialized with a
particular record before validation. For example:

    # Before
    belongs_to :account
    before_validation -> { self.account ||= Current.account }

    # After
    belongs_to :account, default: -> { Current.account }