```ruby
class Book < ActiveRecord::Base
  enum status: [:proposed, :written, :published], _default: :published
end

Book.new.status # => "published"
```

This reverts commit 091164d2, reversing
changes made to dde9e82c.

That issues are caused by using only the model's cast types on the
relation.
To fix that issues, use the attribute's type caster takes precedence
over the model's cast types on the relation.

Fixes #35232.
Fixes #36042.
Fixes #37484.

Testing that when you set a symbol for an enum type, you get a string
back and that when you set a string you also get a string back.

This reverts commit f265e0dd, reversing
changes made to 08dfa921.

Reverted due to surprising behavior for applications. We need to
deprecate this behavior first instead of raising by default.

This behaviour is in
rails/activerecord/lib/active_record/enum.rb #serialize(value) line no 143
if value is not present in mapping we are sending the value back ,
which in mysql returns unrelated record.

I have changed to return nil is value is not present in mapping

Implemented code review changes

Improved test case coverage

[ci skip] - cosmetic changes for better readibility of change log
Signed-off-by: Nak <atulkanswal@gmail.com>

This commit will be squished into f4fbdb1b after maintainer's review.

If `AR::Enum` is used for boolean field, it would be not expected
behavior for us.

fixes #38075

Problem:

In case of using boolean for enum, we can set with string (hash key)
to instance, but we cannot set with actual value (hash value).

```ruby
class Post < ActiveRecord::Base
  enum status: { enabled: true, disabled: false }
end

post.status = 'enabled'
post.status # 'enabled'

post.status = true
post.status # 'enabled'

post.status = 'disabled'
post.status # 'disabled'

post.status = false
post.status # nil (This is not expected behavior)
```

After looking into `AR::Enum::EnumType#cast`, I found that `blank?`
method converts from false value to nil (it seems it may not intentional behavior).

In this patch, I improved that if it defines enum with boolean,
it returns reasonable behavior.

To suppress the following warnings in tests.

```
~/rails/activerecord/lib/active_record/scoping/named.rb:190: warning: method redefined; discarding old not_sent
~/rails/activerecord/lib/active_record/scoping/named.rb:190: warning: previous definition of not_sent was here
```

When a enum element contains the prefix 'not_'. I warns to users
to be aware of this new feature.

Example code:
    class Foo < ActiveRecord::Base
      enum status: [:sent, :not_sent]
    end

[ci skip]

Add negative scopes for all enum values

When defining a Hash enum it can be easy to use [] instead of {}. This
commit checks that only valid definition values are provided, those can
be a Hash, an array of Symbols or an array of Strings. Otherwise it
raises an ArgumentError.

Fixes #33961

Due to inconsistent behavior when chaining scopes and one scope named after a Relation method

Validation code added in 2 places:

- scope, to prevent problematic scope names.
- enum, cause it tries to auto define scope.

`:authors` has a foreign key to `:author_addresses`.
If only `:authors` fixture loaded into the database which supports
foreign key and checks the existing data when enabling foreien keys
like Oracle, it raises the following error

`ORA-02298: cannot validate (ARUNIT.FK_RAILS_94423A17A3) - parent keys not found`

It is because there is no parent data exists in `author_addresses` table.

Here are how other database with foreign key support works:

- MySQL does not check the existing data when enabling foreign key by `foreign_key_checks=1`
https://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_foreign_key_checks
> Setting foreign_key_checks to 1 does not trigger a scan of the existing table data. Therefore, rows added to the table while foreign_key_checks=0 will not be verified for consistency.

- PostgreSQL database itself has a feature to check existing data when
enabling foreign key and discussed at #27636, which is reverted.

Since c51f9b61 changed the "_before_type_cast" expectation for enum.

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

If casted value is nil, generated SQL should be `IS NULL`. But currently
it is generated as `= NULL`. To prevent this behavior, avoid making bind
param if casted value is nil.

Fixes #28945.

Since we have been using this `Arel::Table` since 111ccc83,
in order to properly handle queries, it's important that we properly type cast arguments.

Make name of attribute medium instead of normal

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.

Fixes #25892.

This fixes incorrect assumptions made by e991c7b8 that we can assume the
DB is already casting the value for us. The enum type needs additional
information to perform casting, and needs a subtype.

I've opted not to call `super` in `cast`, as we have a known set of
types which we accept there, and the subtype likely doesn't accept them
(symbol -> integer doesn't make sense)

Close #23190

As described in the "Follow Coding Conventions" section in our
contribution guide (http://edgeguides.rubyonrails.org/contributing_to_ruby_on_rails.html#follow-the-coding-conventions)
we favor `assert_not` over `refute`.

While we don't usually make stylistic changes on it's own I opted to do
it in this case. The reason being that test cases are usually copied as
a starting point for new tests. This results in a spread of `refute` in
files that have been using it already.

After 908cfef6 was introduced fixtures that did not set an enum would
return nil instead of the default enum value.

The fixtures should assume the default if a different enum is not
defined.

The change checks first if the enum is defined in the fixture before
setting it based on the fixture.

Fixes #17511 and #17415

Currently, values for columns backing Active Record enums must be
specified as integers in test fixtures:

    awdr:
      title: "Agile Web Development with Rails"
      status: 2

    rfr:
      title: "Ruby for Rails"
      status: <%= Book.statuses[:proposed] %>

This is potentially confusing, since enum values are typically
specified as symbols or strings in application code. To resolve the
confusion, this change permits the use of symbols or strings to specify
enum values:

    awdr:
      status: :published

It is compatible with fixtures that specify enum values as integers.