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activerecord-slotted_counters

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Active Record extension providing slotted counters support

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# Active Record slotted counters

This gem adds **slotted counters** support to [Active Record counter cache][counter-cache]. Slotted counters help to reduce contention on a single row update in case you have many concurrent operations (like updating a page views counter during traffic spikes).

Read more about slotted counters in [this post](https://planetscale.com/blog/the-slotted-counter-pattern).

<img src="https://cdn.evilmartians.com/badges/logo-no-label.svg" alt="Evil Martians logo" width="22" height="16" /> This project is built by <a href="https://evilmartians.com/">Evil Martians</a>, an American design and engineering consultancy for developer tools, AI, and cybersecurity startups.

## Installation

Add to your project:

```ruby
# Gemfile
gem "activerecord-slotted_counters"
```

### Requirements

- Ruby >= 2.7.0
- Rails 6+

## Usage

First, add and apply the required migration(-s):

```sh
bin/rails generate slotted_counters:install
bin/rails db:migrate
```

Then, add the following line to the model to add a slotted counter:

```ruby
class User < ApplicationRecord
 has_slotted_counter :comments
end
```

Now you can use all the common counter cache APIs as before:

```ruby
# Manipulating the counter explicitly
user = User.first

User.increment_counter(:comments_count, user.id)
User.decrement_counter(:comments_count, user.id)
User.reset_counters(user.id, :comments)
# etc.

# Reading the value
user.comments_count
```

Under the hood, a row in the `slotted_counters` table is created associated with the record.

**NOTE:** Reading the current value performs SQL query once:

```ruby
user.comments_count #=> select * from slotted_counters where ...
user.comments_count #=> no sql
```

If you want to preload counters for multiple records, you can use a convenient `#with_slotted_counters` method:

```ruby
User.all.with_slotted_counters(:comments).find_each do
  _1.comments_count #=> no sql
end
```

Using `counter_cache: true` on `belongs_to` associations also works as expected.

## Contributing

Bug reports and pull requests are welcome on GitHub at [https://github.com/evilmartians/activerecord-slotted_counters](https://github.com/evilmartians/activerecord-slotted_counters).

## Credis

This gem is generated via [new-gem-generator](https://github.com/palkan/new-gem-generator).

## License

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

[counter-cache]: https://api.rubyonrails.org/classes/ActiveRecord/CounterCache/ClassMethods.html

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