The `read_attribute` method always returns the primary key when asked to
read the `id` attribute, even if the primary key isn't named `id`, and
even if another attribute named `id` exists.

For the `inspect`, `attribute_for_inspect` and `pretty_print` methods,
this behaviour is undesirable, as they're used to examine the internal
state of the record. By using `_read_attribute` instead, we'll get the
real value of the `id` attribute.

The `model_metadata` is only used if `model_class` is given.

If `model_class` is given, the `table_name` is always
`model_class.table_name`.

The `@connection` is no longer used since ee5ab222.

Originally the `@connection` was useless because it is only used in
`timestamp_column_names`, which is only used if `model_class` is given.

If `model_class` is given, the `@connection` is always
`model_class.connection`.

It was executing a delete_all method with wrong parameter

Caused at #34196.

[ci skip]

b63701e2 moved the assignment before the query, but we need to capture
our old id before assignment in case we are assigning the id.

Previosly, `update_columns` would just take whatever keys you gave it
and tried to run the update query. Most likely this would result in an
error from the database. However, if the column actually did exist, but
was in `ignored_columns`, this would result in the method returning
successfully when it should have raised, and an attribute that should
not exist written to `@attributes`.

When loading fixtures, Ruby 1.9's hash key ordering means that HABTM
join table rows are always loaded before the parent table rows,
violating foreign key constraints that may be in place. This very
simple change ensures that the parent table's key appears first in the
hash. Violations may still occur if fixtures are loaded in the wrong
order but those instances can be avoided unlike this one.

Any type can be a primary key, so blank string is also valid value.

Closes #26356.

Use column definition with `primary_key: true` instead.

At https://github.com/rails/rails/commit/fc0e3354af7e7878bdd905a95ce4c1491113af9a,

```rb
relation = relation.where(conditions)
```

was rewritten to:

```rb
relation.where!(condition)
```

This change accidentally changed the result of `Topic.exists?({})` from true to false.

To fix this regression, first I moved the blank check logic (`opts.blank?`) from `#where` to `#where!`,
because I thought `#where!` should be identical to `#where`, except that instead of returning a new relation,
it adds the condition to the existing relation.

But on second thought after some discussion on https://github.com/rails/rails/pull/34329,
I started to think that just fixing `#construct_relation_for_exists` is more preferable
than changing `#where` and `#where!`.

Add support for hash and url configs in database hash
of `ActiveRecord::Base.connected_to`.

The PR#31819 changed `#preloaders_on` and added some test,
then #33938 reverted changes that were added to the method in #31819.
Since changes in the method were reverted and as mentioned in the
comment https://github.com/rails/rails/pull/31819#discussion_r221847481
that titles of the tests added in #31819 don't reflect implementation I
think we can remove those test for now.

There are two main reasons why `assert_called_with` should require
`args` argument:

1) If we want to assert that some method should be called and we don't
   need to check with which arguments it should be called then we should use
   `assert_called`.

2) `assert_called_with` without `args` argument doesn't assert anything!
   ```ruby
   assert_called_with(@object, :increment) do
      @object.decrement
   end
   ```
   It causes false assertions in tests that could cause regressions in the project.

I found this bug by working on
[minitest-mock_expectations](https://github.com/bogdanvlviv/minitest-mock_expectations) gem.
This gem is an extension for minitest that provides almost the same method call
assertions.
I was wondering whether you would consider adding "minitest-mock_expectations"
to `rails/rails` instead of private `ActiveSupport::Testing::MethodCallAssertions` module.
If yes, I'll send a patch - https://github.com/bogdanvlviv/rails/commit/a970ecc42c3a9637947599f2c13e3762e4b59208

MySQL 8.0.13 and higher supports default value to be a function or
expression.

https://dev.mysql.com/doc/refman/8.0/en/create-table.html

MySQL 8.0.13 and higher supports functional key parts that index
expression values rather than column or column prefix values.

https://dev.mysql.com/doc/refman/8.0/en/create-index.html

The default collation for utf8mb4 is changed to utf8mb4_0900_ai_ci in
MySQL 8.0, so `test_mysql_connection_collation_is_configured` is
affected by MySQL version and/or default_collation_for_utf8mb4 system
variable.

https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_default_collation_for_utf8mb4

```
% ARCONN=mysql2 be ruby -w -Itest test/cases/adapters/mysql2/connection_test.rb -n test_mysql_connection_collation_is_configured
Using mysql2
Run options: -n test_mysql_connection_collation_is_configured --seed 10421

# Running:

F

Failure:
Mysql2ConnectionTest#test_mysql_connection_collation_is_configured [test/cases/adapters/mysql2/connection_test.rb:108]:
Expected: "utf8mb4_general_ci"
  Actual: "utf8mb4_0900_ai_ci"

rails test test/cases/adapters/mysql2/connection_test.rb:106

Finished in 0.013842s, 72.2450 runs/s, 144.4900 assertions/s.
1 runs, 2 assertions, 1 failures, 0 errors, 0 skips
```

Since #33844, eager loading/preloading with too many and/or too large
ids won't be broken by pre-checking whether the value is constructable
or not.

But the pre-checking caused the type to be evaluated at relation build
time instead of at the query execution time, that is breaking an
expectation for some apps.

I've made the pre-cheking lazy as much as possible, that is no longer
happend at relation build time.

when user has no parent table access privileges

Refer https://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-13.html#mysqld-8-0-13-errors

>>
* Previously, the ER_NO_REFERENCED_ROW_2 and ER_ROW_IS_REFERENCED_2 error messages
for foreign key operations were displayed and revealed information about parent tables,
even when the user had no parent table access privileges. Error handling for this situation has been revised:

  * If the user does have table-level privileges for all parent tables,
    ER_NO_REFERENCED_ROW_2 and ER_ROW_IS_REFERENCED_2 are displayed, the same as before.

  * If the user does not have table-level privileges for all parent tables,
    more generic error messages are displayed instead (ER_NO_REFERENCED_ROW and ER_ROW_IS_REFERENCED).
<<

This pull request addresses these 3 failures:

```ruby
$ ARCONN=mysql2 bundle exec ruby -w -Itest test/cases/adapter_test.rb -n /foreign/
Using mysql2
Run options: -n /foreign/ --seed 14251

F

Failure:
ActiveRecord::AdapterForeignKeyTest#test_foreign_key_violations_are_translated_to_specific_exception_with_validate_false [test/cases/adapter_test.rb:348]:
[ActiveRecord::InvalidForeignKey] exception expected, not
Class: <ActiveRecord::StatementInvalid>
Message: <"Mysql2::Error: Cannot add or update a child row: a foreign key constraint fails: INSERT INTO `fk_test_has_fk` (`fk_id`) VALUES (1231231231)">

... snip ...

rails test test/cases/adapter_test.rb:343

F

Failure:
ActiveRecord::AdapterForeignKeyTest#test_foreign_key_violations_on_delete_are_translated_to_specific_exception [test/cases/adapter_test.rb:368]:
[ActiveRecord::InvalidForeignKey] exception expected, not
Class: <ActiveRecord::StatementInvalid>
Message: <"Mysql2::Error: Cannot delete or update a parent row: a foreign key constraint fails: DELETE FROM fk_test_has_pk WHERE pk_id = 1">

... snip ...

rails test test/cases/adapter_test.rb:365

F

Failure:
ActiveRecord::AdapterForeignKeyTest#test_foreign_key_violations_on_insert_are_translated_to_specific_exception [test/cases/adapter_test.rb:358]:
[ActiveRecord::InvalidForeignKey] exception expected, not
Class: <ActiveRecord::StatementInvalid>
Message: <"Mysql2::Error: Cannot add or update a child row: a foreign key constraint fails: INSERT INTO fk_test_has_fk (fk_id) VALUES (0)">

... snip ...

rails test test/cases/adapter_test.rb:357

Finished in 0.087370s, 34.3366 runs/s, 34.3366 assertions/s.
3 runs, 3 assertions, 3 failures, 0 errors, 0 skips
$
```

When `attr_name` is passed as a symbol, it's currently converted to a
string by `attribute_alias?`, and potentially also `attribute_alias`,
as well as by the `read_attribute`/`write_attribute` method itself.

By converting `attr_name` to a string up front, the extra allocations
related to attribute aliases can be avoided.

AR instance support `filter_parameters` since #33756.
Though Regex or Proc is valid as `filter_parameters`,
they are not supported as AR#inspect.

I also add :mask option and #filter_params to
`ActiveSupport::ParameterFilter#new` to implement this.

Follow up #32146.

`init_with` and `init_from_db` are almost the same code except decode
`coder`.

And also, named `init_from_db` is a little misreading, a raw values hash
from the database is already converted to an attributes object by
`attributes_builder.build_from_database`, so passed `attributes` in that
method is just an attributes object.

I renamed that method to `init_with_attributes` since the method is
shared with `init_with` to initialize an empty model object.

I don't prefer to extract it for one adapter even though all adapters
also does.

Related to #34227.

Will allow sub classes to override the protected
`#check_version` method hook if desired.

For example, this will be most helpful in sub classes that wish
to support lazy initialization because the version check can
be postponed until the connection is ready to be initialized.

Starting in Rails 5.0.0 and still present in Rails 5.2.1, `singular_ids`
got memoized and didn't reload after more items were added to the
relation.

Although 19c80718 happens to fix the issue, it only adds tests for
`has_many` relations while this bug only affected
`has_and_belongs_to_many` relations.

This commit adds a regression test to ensure it never happens again with
`habtm` relations.

Ensures #34179 never gets reproduced.

Change query to use alias name for timestamp_column to avoid ambiguity problems when using timestamp from subquery.

This is an alternative to https://github.com/rails/rails/pull/34195

The active record `respond_to?` method needs to do two things if `super` does not say that the method exists. It has to see if the "name" being passed in represents a column in the table. If it does then it needs to pass it to `has_attribute?` to see if the key exists in the current object. The reason why this is slow is that `has_attribute?` needs a string and most (almost all) objects passed in are symbols.

The only time we need to allocate a string in this method is if the column does exist in the database, and since these are a limited number of strings (since column names are a finite set) then we can pre-generate all of them and use the same string. 

We generate a list hash of column names and convert them to symbols, and store the value as the string name. This allows us to both check if the "name" exists as a column, but also provides us with a string object we can use for the `has_attribute?` call. 

I then ran the test suite and found there was only one case where we're intentionally passing in a string and changed it to a symbol. (However there are tests where we are using a string key, but they don't ship with rails).

As re-written this method should never allocate unless the user passes in a string key, which is fairly uncommon with `respond_to?`.

This also eliminates the need to special case every common item that might come through the method via the `case` that was originally added in https://github.com/rails/rails/commit/f80aa5994603e684e3fecd3f53bfbf242c73a107 (by me) and then with an attempt to extend in https://github.com/rails/rails/pull/34195.

As a bonus this reduces 6,300 comparisons (in the CodeTriage app homepage) to 450 as we also no longer need to loop through the column array to check for an `include?`.

`developers.name desc` was added at d59f3a78, but any test case isn't
failed even if the `developers.name desc` is removed since all tested
developers are consistently ordered on both `name` and `id`.

I changed one developers creation ordering to ensure to test that
`project.developers` is ordered by `developers.name desc`.

Ruby uses the original method name, so will show the __temp__ method
name in the backtrace. However, in the common case the method name
is compatible with the `def` keyword, so we can avoid the __temp__
method name in that case to improve the name shown in backtraces
or TracePoint#method_id.

This PR adds the ability to 1) connect to multiple databases in a model,
and 2) switch between those connections using a block.

To connect a model to a set of databases for writing and reading use
the following API. This API supercedes `establish_connection`. The
`writing` and `reading` keys represent handler / role names and
`animals` and `animals_replica` represents the database key to look up
the configuration hash from.

```
class AnimalsBase < ApplicationRecord
  connects_to database: { writing: :animals, reading: :animals_replica }
end
```

Inside the application - outside the model declaration - we can switch
connections with a block call to `connected_to`.

If we want to connect to a db that isn't default (ie readonly_slow) we
can connect like this:

Outside the model we may want to connect to a new database (one that is
not in the default writing/reading set) - for example a slow replica for
making slow queries. To do this we have the `connected_to` method that
takes a `database` hash that matches the signature of `connects_to`. The
`connected_to` method also takes a block.

```
AcitveRecord::Base.connected_to(database: { slow_readonly: :primary_replica_slow }) do
  ModelInPrimary.do_something_thats_slow
end
```

For models that are already loaded and connections that are already
connected, `connected_to` doesn't need to pass in a `database` because
you may want to run queries against multiple databases using a specific
role/handler.

In this case `connected_to` can take a `role` and use that to swap on
the connection passed. This simplies queries - and matches how we do it
in GitHub. Once you're connected to the database you don't need to
re-connect, we assume the connection is in the pool and simply pass the
handler we'd like to swap on.

```
ActiveRecord::Base.connected_to(role: :reading) do
  Dog.read_something_from_dog
  ModelInPrimary.do_something_from_model_in_primary
end
```