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An ActiveRecord extension for writing commonly useful atomic SQL statements to avoid race condition.

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# Atomically

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`atomically` is a Ruby Gem for you to write atomic query with ease.

All methods are defined in `Atomically::QueryService` instead of defining in `ActiveRecord` directly, in order not to pollute the model instance.

## Supports
- Ruby 2.2 ~ 2.7, 3.0, 3.2
- Rails 3.2, 4.2, 5.0, 5.1, 5.2, 6.0, 7.2
- MySQL, PostgreSQL

## Table of contents

1. [Installation](#installation)
2. [Methods](#methods)
   - Relation Methods
     - [create_or_plus](#create_or_plus-columns-values-on_duplicate_update_columns-conflict_target)
     - [pay_all](#pay_all-hash-update_columns-primary_key-id)
     - [update_all](#update_all-expected_number-updates)
     - [update_all_and_get_ids](#update_all_and_get_ids-updates)
   - Model Methods
     - [update](#update-attrs-from-not_set)
     - [decrement_unsigned_counters](#decrement_unsigned_counters-counters)
3. [Development](#development)
4. [Contributing](#contributing)
5. [License](#license)

## Installation

Add this line to your application's Gemfile:

```ruby
gem 'atomically'
```

And then execute:

$ bundle

Or install it yourself as:

$ gem install atomically

## Methods

Note: ActiveRecord validations and callbacks will **NOT** be triggered when calling below methods.

### create_or_plus _(columns, values, on_duplicate_update_columns, conflict_target:)_

Import an array of records. When key is duplicate, plus the old value with new value.
It is useful to add `items` to `user` when `user_items` may not exist. (Let `User` and `Item` are many-to-many relationship.)

#### Parameters

- First two args (`columns`, `values`) are the same with the [import](https://github.com/zdennis/activerecord-import#columns-and-arrays) method.
  - `on_duplicate_update_columns` - The column that will be updated on duplicate.
  - `conflict_target` - Needed only in pg. Specifies which columns have unique index.

#### Example

```rb
class User < ApplicationRecord
  has_many :user_items
  has_many :items, through: :user_items
end

class UserItem < ApplicationRecord
  belongs_to :user
  belongs_to :item
end

class Item < ApplicationRecord
  has_many :user_items
  has_many :users, through: :user_items
end

user = User.find(2)
item1 = Item.find(1)
item2 = Item.find(2)
```

```rb
columns = [:user_id, :item_id, :quantity]
values = [[user.id, item1.id, 3], [user.id, item2.id, 2]]

# mysql
UserItem.atomically.create_or_plus(columns, values, [:quantity])

# pg
UserItem.atomically.create_or_plus(columns, values, [:quantity], conflict_target: [:user_id, :item_id])
```

before

![before](https://user-images.githubusercontent.com/4011729/67365648-95e89480-f5a4-11e9-8147-279385c6f442.png)

after

![after](https://user-images.githubusercontent.com/4011729/67365653-97b25800-f5a4-11e9-8314-8e6ff8d2cd61.png)

#### SQL queries

```sql
# mysql
INSERT INTO `user_items` (`user_id`,`item_id`,`quantity`,`created_at`,`updated_at`) VALUES
  (2,1,3,'2018-11-27 03:44:25','2018-11-27 03:44:25'),
  (2,2,2,'2018-11-27 03:44:25','2018-11-27 03:44:25')
ON DUPLICATE KEY UPDATE
  `quantity` = `quantity` + VALUES(`quantity`)

# pg
INSERT INTO "user_items" ("user_id","item_id","quantity","created_at","updated_at") VALUES
  (2,1,3,'2018-11-27 03:44:25.847909','2018-11-27 03:44:25.847909'),
  (2,2,2,'2018-11-27 03:44:25.847909','2018-11-27 03:44:25.847909')
ON CONFLICT (user_id, item_id) DO UPDATE SET
  "quantity" = "user_items"."quantity" + excluded."quantity"  RETURNING "id"
```

---
### pay_all _(hash, update_columns, primary_key: :id)_

Reduce the quantity of items and return how many rows and updated if all of them are enough.
Do nothing and return zero if any of them is not enough.

#### Parameters

- `hash` - A hash contains the id of the models as keys and the amount to update the field by as values.
  - `update_columns` - The column that will be updated.
  - `primary_key` - Specify the column that `id`(the key of hash) refers to.

#### Example

```rb
user.user_items.atomically.pay_all({ item1.id => 4, item2.id => 3 }, [:quantity], primary_key: :item_id)
# => 2 (if success)
# => 0 (if some aren't enough)
```

#### SQL queries

```sql
UPDATE `user_items` SET `quantity` = `quantity` + (@change :=
  CASE `item_id`
  WHEN 1 THEN -4
  WHEN 2 THEN -3
  END)
WHERE `user_items`.`user_id` = 1 AND (
  `user_items`.`item_id` = 1 AND (`quantity` >= 4) OR `user_items`.`item_id` = 2 AND (`quantity` >= 3)
) AND (
  (
    SELECT COUNT(*) FROM (
      SELECT `user_items`.* FROM `user_items`
      WHERE `user_items`.`user_id` = 1 AND (
        `user_items`.`item_id` = 1 AND (`quantity` >= 4) OR `user_items`.`item_id` = 2 AND (`quantity` >= 3)
      )
    ) subquery
  ) = 2
)
```

---
### update_all _(expected_number, updates)_

Behaves like [ActiveRecord::Relation#update_all](https://apidock.com/rails/ActiveRecord/Relation/update_all) but add an additional constrain that the number of affected rows equals to what you specify.

#### Parameters

- `expected_number` - The number of rows that you expect to be updated.
  - `updates` - A string, array, or hash representing the SET part of an SQL statement.

#### Examples
```rb
User.where(id: [5, 6]).atomically.update_all(2, name: '')
# => 2 (success)

User.where(id: [7, 8, 9]).atomically.update_all(2, name: '')
# => 0 (fail)
```

#### SQL queries

```sql
# User.where(id: [7, 8, 9]).atomically.update_all(2, name: '')
UPDATE `users` SET `users`.`name` = '' WHERE `users`.`id` IN (7, 8, 9) AND (
  (
    SELECT COUNT(*) FROM (
      SELECT `users`.* FROM `users` WHERE `users`.`id` IN (7, 8, 9)
    ) subquery
  ) = 2
)
```

---
### update_all_and_get_ids _(updates)_

Behaves like [ActiveRecord::Relation#update_all](https://apidock.com/rails/ActiveRecord/Relation/update_all), but return an array of updated records' id instead of the number of updated records.

#### Parameters

- `updates` - A string, array, or hash representing the SET part of an SQL statement.

#### Example

```rb
User.where(account: ['moon', 'wolf']).atomically.update_all_and_get_ids('money = money + 1')
# => [254, 371] (array of updated user ids)

User.where(account: ['moon', 'wolf']).update_all('money = money + 1')
# => 2 (the number of updated records)
```

#### SQL queries

```sql
# mysql
BEGIN
  SET @ids := NULL
  UPDATE `users` SET money = money + 1 WHERE `users`.`account` IN ('moon', 'wolf') AND ((SELECT @ids := CONCAT_WS(',', `users`.`id`, @ids)))
  SELECT @ids FROM DUAL
COMMIT

# pg
UPDATE 'users' SET money = money + 1 RETURNING id
```

---
### update _(attrs, from: :not_set)_

Updates the attributes of the model from the passed-in hash and saves the record. Return true if update successfully, false otherwise. This method can detect race condition and make sure the model is updated only once.

The difference between this method and [ActiveRecord#update](https://apidock.com/rails/ActiveRecord/Persistence/update) is that it will add extra WHERE conditions to prevent race condition.

#### Parameters

- `attrs` - Same with the first parameter of [ActiveRecord#update](https://apidock.com/rails/ActiveRecord/Persistence/update)
  - `from` - The value before update. If not set, use the current attriutes of the model.

#### Example

```rb
class Arena < ApplicationRecord
  def atomically_close!
    atomically.update(closed_at: Time.now)
  end

def close!
    update(closed_at: Time.now)
  end
end
```

Let `arena.closed_at` be nil.

```rb
arena.atomically_close!
# => true (if success)
# => false (if race condition occurs)
```

The return value can be used to prevent race condition and make sure some piece of code is executed only once.

```rb
if arena.atomically_close!
  # Only one request can pass this check and execute the code here.
  # You can send rewards, calculate ranking, or fire background job here.
  # No need to worry about being invoked multiple times.
  do_something
end
```

#### SQL queries

```sql
# arena.atomically_close!
UPDATE `arenas` SET `arenas`.`closed_at` = '2018-11-27 03:44:25', `updated_at` = '2018-11-27 03:44:25'
WHERE `arenas`.`id` = 1752 AND `arenas`.`closed_at` IS NULL

# arena.close!
UPDATE `arenas` SET `arenas`.`closed_at` = '2018-11-27 03:44:25', `updated_at` = '2018-11-27 03:44:25'
WHERE `arenas`.`id` = 1752
```

---
### decrement_unsigned_counters _(counters)_

Decrement numeric fields via a direct SQL update, and make sure that it will not become negative.

Return true if update successfully, false otherwise.

#### Parameters

- `counters` - A Hash containing the names of the fields to update as keys and the amount to update the field by as values.

#### Example

```rb
user.money
# => 100

user.atomically.decrement_unsigned_counters(money: 10)
# => true (success)
user.reload.money
# => 90

user.atomically.decrement_unsigned_counters(money: 999)
# => false (fail)
user.reload.money
# => 90
```

#### SQL queries

```sql
# user.atomically.decrement_unsigned_counters(money: 140)
UPDATE `users` SET money = money - 140 WHERE `users`.`id` = 1 AND (money >= 140)
```

## Development

After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake test DB=mysql` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).

## Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/khiav223577/atomically. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [Contributor Covenant](http://contributor-covenant.org) code of conduct.

## License

The gem is available as open source under the terms of the [MIT License](http://opensource.org/licenses/MIT).

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