In practical terms, this allows serialized columns and tz aware columns
to be used in wheres that go through joins, where they previously would
not behave correctly. Internally, this removes 1/3 of the cases where we
rely on Arel to perform type casting for us.

There were two non-obvious changes required for this. `update_all` on
relation was merging its bind values with arel's in the wrong order.
Additionally, through associations were assuming there would be no bind
parameters in the preloader (presumably because the where would always
be part of a join)

[Melanie Gilman & Sean Griffin]

We were relying on hash inequality in tests

This fixes <"SQLite3::SQLException: no such column: legacy_things.person_id: SELECT \"legacy_things\".* FROM \"legacy_things\" WHERE \"legacy_things\".\"person_id\" = ?">
in OptimisticLockingTest#test_lock_destroy

with dynamic conditions.

Fixes #16128

This bug was introduced in https://github.com/rails/rails/commit/c35e438620f2d56562251571377995359546393d
so it's present from 4.1.2-rc1 and after.

https://github.com/rails/rails/commit/c35e438620f2d56562251571377995359546393d
merges any relation scopes passed as proc objects to the relation,
but does *not* take into account the arity of the lambda.

To reproduce: https://gist.github.com/Agis-/5f1f0d664d2cd08dfb9b

As per discussion, this changes the model generators to specify
`null: false` for timestamp columns. A warning is now emitted if
`timestamps` is called without a `null` option specified, so we can
safely change the behavior when no option is specified in Rails 5.

by using shorter attribute names.

This reverts commit e84799d9, e31104c1 and e6ca8e2c

This was previously fixed in e84799d9 but broken in 3f596f8a. This commit
reintroduced the conditional that prevents the foreign keys from being
added to MySQL databases.

The name of the foreign key is not relevant from a users perspective.
Using random names resolves the urge to rename the foreign key when the
respective table or column is renamed.

Reliant on https://github.com/rails/rails/pull/15747 but pulled to a
separate PR to reduce noise. `has_many :through` associations have the
undocumented behavior of automatically detecting counter caches.
However, the way in which it does so is inconsistent with counter caches
everywhere else, and doesn't actually work consistently.

As with normal `has_many` associations, the user should specify the
counter cache on the `belongs_to`, if they'd like it updated.

Now the following case will work fine

    class Tag < ActiveRecord::Base
    end

    class Publisher::Article < ActiveRecord::Base
      has_and_belongs_to_many :tags
    end

Fixes #15761

use name specified by 'as' for automatic inverse association to avoid reflecting on wrong association

This reverts commit dd3ea171 and add a
regression test.

Fixes #15418

As a result of all of the refactoring that's been done, it's now
possible for us to define a public API to allow users to specify
behavior. This is an initial implementation so that I can work off of it
in smaller pieces for additional features/refactorings.

The current behavior will continue to stay the same, though I'd like to
refactor towards the automatic schema detection being built off of this
API, and add the ability to opt out of automatic schema detection.

Use cases:

- We can deprecate a lot of the edge cases around types, now that there
  is an alternate path for users who wish to maintain the same behavior.
- I intend to refactor serialized columns to be built on top of this
  API.
- Gem and library maintainers are able to interact with `ActiveRecord`
  at a slightly lower level in a more stable way.
- Interesting ability to reverse the work flow of adding to the schema.
  Model can become the single source of truth for the structure. We can
  compare that to what the database says the schema is, diff them, and
  generate a migration.

* * *

This bug can be triggered when serializing record R (the instance) of type C
(the class), provided that the following conditions are met:

1. The name of one or more columns/attributes on C/R matches an existing private
   method on C (e.g. those defined by `Kernel`, such as `format`).

2. The attribute methods have not yet been generated on C.

In this case, the matching private methods will be called by the serialization
code (with no arguments) and their return values will be serialized instead. If
the method requires one or more arguments, it will result in an `ArgumentError`.

This regression is introduced in d1316bb1.

* * *

Attribute methods (e.g. `#name` and `#format`, assuming the class has columns
named `name` and `format` in its database table) are lazily defined. Instead of
defining them when a the class is defined (e.g. in the `inherited` hook on
`ActiveRecord::Base`), this operation is deferred until they are first accessed.

The reason behind this is that is defining those methods requires knowing what
columns are defined on the database table, which usually requires a round-trip
to the database. Deferring their definition until the last-possible moment helps
reducing unnessary work, especially in development mode where classes are
redefined and throw away between requests.

Typically, when an attribute is first accessed (e.g. `a_book.format`), it will
fire the `method_missing` hook on the class, which triggers the definition of
the attribute methods. This even works for methods like `format`, because
calling a private method with an explicit receiver will also trigger that hook.

Unfortunately, `read_attribute_for_serialization` is simply an alias to `send`,
which does not respect method visibility. As a result, when serializing a record
with those conflicting attributes, the `method_missing` is not fired, and as a
result the attribute methods are not defined one would expected.

Before d1316bb1, this is negated by the fact that calling the `run_callbacks`
method will also trigger a call to `respond_to?`, which is another trigger point
for the class to define its attribute methods. Therefore, when Active Record
tries to run the `after_find` callbacks, it will also define all the attribute
methods thus masking the problem.

* * *

The proper fix for this problem is probably to restrict `read_attribute_for_serialization`
to call public methods only (i.e. alias `read_attribute_for_serialization` to
`public_send` instead of `send`). This however would be quite risky to change
in a patch release and would probably require a full deprecation cycle.

Another approach would be to override `read_attribute_for_serialization` inside
Active Record to force the definition of attribute methods:

   def read_attribute_for_serialization(attribute)
     self.class.define_attribute_methods
     send(attribute)
   end

Unfortunately, this is quite likely going to cause a performance degradation.

This patch therefore restores the behaviour from the 4-0-stable branch by
explicitly forcing the class to define its attribute methods in a similar spot
(when records are initialized). This should not cause any extra roundtrips to
the database because the `@columns` should already be cached on the class.

Fixes #15188.

This reverts commit 9a1abedc, reversing
changes made to c72d6c91.

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/test/models/comment.rb

This change break integration with activerecord-deprecated_finders so
I'm reverting until we find a way to make it work with this gem.

The foreign_key could be `String` and just doing `owners_map[owner_key]`
could return `nil`.
To prevent this bug, we should `to_s` both keys if their types are
different.

Fixes #14734.

Thank's for @laurocaetano for the help with tests. 😃

Fixes #14709

Changed the call to a scope block to be evaluated with instance_eval.
The result is that ScopeRegistry can use the actual class instead of base_class when
caching scopes so queries made by classes with a common ancestor won't leak scopes.

There is no reason for the PG adapter to have a default limit of 255 on :string
columns. See this snippet from the PG docs:

    Tip: There is no performance difference among these three types, apart
    from increased storage space when using the blank-padded type, and a
    few extra CPU cycles to check the length when storing into a
    length-constrained column. While character(n) has performance
    advantages in some other database systems, there is no such advantage
    in PostgreSQL; in fact character(n) is usually the slowest of the
    three because of its additional storage costs. In most situations text
    or character varying should be used instead.

It was causing error when using `with_options` passing a lambda as its
last argument.

    class User < ActiveRecord::Base
      with_options dependent: :destroy do |assoc|
        assoc.has_many :profiles, -> { where(active: true) }
      end
    end

It was happening because the `option_merger` was taking the last
argument and checking if it was a Hash. This breaks the HasMany usage,
because its last argument can be a Hash or a Proc.

As the behavior described in this test:
https://github.com/rails/rails/blob/master/activesupport/test/option_merger_test.rb#L69
the method will only accept the lambda, this way it will keep the expected behavior. See 9eaa0a34

conflicting private method defined on its ancestors.

The problem is that `method_defined_within?(name, klass, superklass)`
only works correclty when `klass` and `superklass` are both `Class`es.

If both `klass` and `superklass` are both `Class`es, they share the
same inheritance chain, so if a method is defined on `klass` but not
`superklass`, this method must be introduced at some point between
`klass` and `superklass`.

This does not work when `superklass` is a `Module`. A `Module`'s
inheritance chain contains just itself. So if a method is defined on
`klass` but not on `superklass`, the method could still be defined
somewhere upstream, e.g. in `Object`.

This fix works by avoiding calling `method_defined_within?` with a
module while still fufilling the requirement (checking that the
method is defined withing `superclass` but not is not a generated
attribute method).

4d8ee288 is likely an attempted partial fix for this problem. This
unrolls that fix and properly check the `superclass` as intended.

Fixes #11569.

The `subclass_from_attrs` method is called even if the column specified by
the `inheritance_column` setting doesn't exist. This prevents setting associations
via the attributes hash if the association name clashes with the value of the setting,
typically `:type`. This worked previously in Rails 3.2.

Fixes: #11524

Renaming the test accordingly to its behaviour

Adding 'Fixes' statement to changelog

Improving tests legibility & changelog

Undoing mistakenly removed empty line & further improving changelog

Previously, this would give an `ArgumentError`:

   class Issue < ActiveRecord::Base
     enum :status, [:open, :finished]
   end

   Issue.open.build # => ArgumentError: '0' is not a valid status
   Issue.open.create # => ArgumentError: '0' is not a valid status

PR #13542 muted the error, but the issue remains. This commit fixes
the issue by allowing the enum value to be written directly via the
setter:

   Issue.new.status = 0 # This now sets status to :open

Assigning a value directly via the setter like this is not part of the
documented public API, so users should not rely on this behavior.

Closes #13530.

Previously, the writer methods would simply check whether the passed
argument was the symbol representing the integer value of an enum field.
Therefore, it was not possible to specify the numeric value itself but
the dynamically defined scopes generate where clauses relying on this
kind of values so a chained call to a method like `find_or_initialize_by`
would trigger an `ArgumentError`.

Reference #13530

The dynamic finder was creating the method signature with the parameters name,
which may have reserved words and this way creating invalid Ruby code.

Closes: #13261

    Example:

        # Before
        Dog.find_by_alias('dog name')

        # Was creating this method
        def self.find_by_alias(alias, options = {})

        # After
        Dog.find_by_alias('dog name')

        # Will create this method
        def self.find_by_alias(_alias, options = {})