This reverts commit f6ca7e4e75408bc42f515fc7206d6c6ff0dce7c6.
The default collation of utf8 in MySQL is the `utf8_general_ci`, and
this should not be changed. This is because, the better collation in the
all locales is not exists, optimal collation in own application is not
known other than themselves.
The `utf8_unicode_ci` is known as Japanese killer in Japan, there are
serious impacts in search of Japanese.
MySQL implements the `utf8_unicode_ci` according to the Unicode
Collation Algorithm (UCA) described at http://www.unicode.org/reports/tr10/,
but the `utf8_unicode_ci` have only partial support for the UCA, only
primary level key comparison implemented (also known as L1 (Base
characters) comparison).
Because L1 (Base characters) comparison does not distinguish between the
presence or absence of the accent, if distinction of the accent is
important there is a serious impact (e.g. Japanese).
Example:
```
> SHOW CREATE TABLE `dicts`\G
*************************** 1. row ***************************
Table: dicts
Create Table: CREATE TABLE `dicts` (
`word` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
`meaning` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
1 row in set (0.00 sec)
> INSERT INTO `dicts` VALUES ('ハハ', 'mother'), ('パパ', 'father');
Query OK, 2 rows affected (0.00 sec)
> SELECT * FROM `dicts` WHERE `word` = 'ハハ';
+--------+---------+
| word | meaning |
+--------+---------+
| ハハ | mother |
| パパ | father |
+--------+---------+
2 rows in set (0.00 sec)
> CREATE UNIQUE INDEX `unique_index_word` ON `dicts`(`word`);
ERROR 1062 (23000): Duplicate entry 'ハハ' for key 'unique_index_word'
```
We should omit the collation entirely rather than providing a default.
Then the choice is the responsibility of the server and MySQL distribution.
- Addresses issue #22092
- Works on Postgres and MySQL
- Uses advisory locks because of two important properties:
1. The can be obtained outside of the context of a transaction
2. They are automatically released when the session ends, so if a
migration process crashed for whatever reason the lock is not left
open perpetually
- Adds get_advisory_lock and release_advisory_lock methods to database
adapters
- Attempting to run a migration while another one is in process will
raise a ConcurrentMigrationError instead of attempting to run in
parallel with undefined behavior. This could be rescued and
the migration could exit cleanly instead. Perhaps as a configuration
option?
Technical Notes
==============
The Migrator uses generate_migrator_advisory_lock_key to build the key
for the lock. In order to be compatible across multiple adapters there
are some constraints on this key.
- Postgres limits us to 64 bit signed integers
- MySQL advisory locks are server-wide so we have to scope to the
database
- To fulfil these requirements we use a Migrator salt (a randomly
chosen signed integer with max length of 31 bits) that identifies
the Rails migration process as the owner of the lock. We multiply
this salt with a CRC32 unsigned integer hash of the database name to
get a signed 64 bit integer that can also be converted to a string
to act as a lock key in MySQL databases.
- It is important for subsequent versions of the Migrator to use the
same salt, otherwise different versions of the Migrator will not see
each other's locks.
This assumes only one query was ever executed, but it appears to
sometimes be loading schema information. We can just look at the array
of queries, rather than the "first" one that was run
We are using the same version constraint in the database adapters so
when a new version of the adapter that doesn't work with the version of
rails is released we don't break new applications.
Before this commit, if
`ActiveRecord::Base.belongs_to_required_by_default` is set to `true`,
then creating a record through `has_and_belongs_to_many` fails with the
cryptic error message `Left side must exist`. This is because
`inverse_of` isn't working properly in this case, presumably since we're
doing trickery with anonymous classes in the middle.
Rather than following this rabbit hole to try and get `inverse_of` to
work in a case that we know is not publicly supported, we can just turn
off this validation to match the behavior of 4.2 and earlier.
rather than an action name and *args. The *args were not being used in regular
applications outside tests. This causes a backwards compatibility
issue, but reduces array allocations for most users.
`dispatch` sets the request and response on the controller for us
automatically, so the test harness doesn't need to know the internals of
how request / response is set.
Conflicts:
actionpack/lib/action_controller/test_case.rb
This is part of a refactoring to make it easier to allow `order` to use
sanitize like just about everything else on relation. The deleted test
doesn't give any reasoning as to why passing `nil` to `order` needs to
be supported, and it's rather nonsensical. I can almost see allowing an
empty string being passed (though I'm tempted to just disallow it...)
The stated value of `now` would actually give the same result for
`now - 24.hours` and `now - 1.day`. Use an alternative value for
`now` that demonstrates the difference between subtracting
`24.hours` and `1.day`.
