Currently `CollectionProxy` inherits `Relation` and `Relation` includes
`QueryMethods`. This method is completely duplicated.

https://github.com/rails/rails/blob/v5.0.0/activerecord/lib/active_record/relation/query_methods.rb#L271-L275

`#second`, `#third`, etc finder methods was added in 03855e79.
But the signature of these methods is inconsistent with the original
finder methods. And also the signature of `#first` and `#last` methods
is different from the original. This commit fixes the inconsistency.

`#first`, `#second`, ..., `#last` methods respects dirty target. But
`#take` doesn't respect it. This commit fixes the inconsistent behavior.

Some case expressions remain, need to think about those ones.

Because `scope` (`target_scope`) is a `AssociationRelation`.
`AssociationRelation` handles `set_inverse_instance`.

https://github.com/rails/rails/blob/v5.0.0/activerecord/lib/active_record/association_relation.rb#L31-L33

See also #26022.

Because `scope` (`target_scope`) is a `AssociationRelation`.
`AssociationRelation` handles `set_inverse_instance`.

https://github.com/rails/rails/blob/v5.0.0/activerecord/lib/active_record/association_relation.rb#L31-L33

[ci skip]

Ruby 2.4 unifies Fixnum and Bignum into Integer: https://bugs.ruby-lang.org/issues/12005

* Forward compat with new unified Integer class in Ruby 2.4+.
* Backward compat with separate Fixnum/Bignum in Ruby 2.2 & 2.3.
* Drops needless Fixnum distinction in docs, preferring Integer.

Changed id-writer to save join table records based on association primary key

When same association is loaded in the model creation callback
The new object is inserted into association twice

When `require 'active_support/rails'`, 'active_support/deprecation'
is automatically loaded.

If the through class has default scopes we should skip the statement
cache.

Closes #20745.

Fixes #21082

remove extra space

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.

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.

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.

Instead use .scope_attributes? consistently in ActiveRecord to check whether
there are attributes currently associated with the scope.

Move the implementation of .scope_attributes? and .scope_attributes to
ActiveRecord::Scoping because they don't particularly have to do specifically
with Named scopes and their only dependency, in the case of
.scope_attributes?, and only caller, in the case of .scope_attributes is
contained in Scoping.

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]

There are many ways that things end up getting passed to `concat`. Not
all of those entry points called `flatten` on their input. It seems that
just about every method that is meant to take a single record, or that
splats its input, is meant to also take an array. `concat` is the
earliest point that is common to all of the methods which add records to
the association. Partially fixes #18689

The records weren't being replaced since equality in Active Record is
defined in terms of `id` only. It is reasonable to expect that the
references would be replaced in memory, even if no queries are actually
executed. This change did not appear to affect any other parts of the
code base. I chose not to execute callbacks since we're not actually
modifying the association in a way that will be persisted.

Fixes #17730

I grepped the source code for code snippets wrapped in backticks in the comments
and replaced the backticks with plus signs so they are correctly displayed in
the Rails documentation.

[ci skip]

if you specify a default scope on a model, it will break caching.  We
cannot predict what will happen inside the scope, so play it safe for
now.  fixes #17495

follow up for #17052

Fix that a collection proxy could be cached before the save of the owner, resulting in an invalid proxy lacking the owner’s id.

Absent this fix calls like: owner.association.update_all to behave unexpectedly because they try to act on association objects where
owner_id is null.

more evidence here: https://gist.github.com/Empact/5865555
```
Active Record 3.2.13
-- create_table(:firms, {:force=>true})
   -> 0.1371s
-- create_table(:clients, {:force=>true})
   -> 0.0005s
1 clients. 1 expected.
1 clients updated. 1 expected.
```

```
Active Record 4.0.0
-- create_table(:firms, {:force=>true})
   -> 0.1606s
-- create_table(:clients, {:force=>true})
   -> 0.0004s
1 clients. 1 expected.
0 clients updated. 1 expected.
```

Eagerly loaded collection and singular associations are ignored by the StatementCache, which causes errors when the queries they generate reference columns that were not eagerly loaded.

This commit skips the creation of the StatementCache as a fix for these scenarios.

In some cases there is a difference between the two, we should always
be doing one or the other. For convenience, `type_cast` is still a
private method on type, so new types that do not need different behavior
don't need to implement two methods, but it has been moved to private so
it cannot be used accidentally.

When delete or destroy is called on all records nothing
is deleted or destroyed. Intead of running through the code and still
not deleteing anything, we should early return

Rename delete_all_records because this name better describes
what the method is doing. We can then remove :all from the
hm:t version and pull out the unoptimized call to load_target
in delete_records and pass it directly.