Cache Key Versioning in Rails

cache_key_with_version is a method used in Ruby on Rails to generate a cache key for a model object that includes its version number. This method is helpful for ensuring cache consistency, as it combines the object’s unique ID, updated timestamp, and a version number to create a unique cache key.

How it Works

The cache_key_with_version method is available in Rails models that include ActiveRecord::Base. It generates a cache key by combining:

Model Name: The name of the model.
ID: The primary key of the record.
Updated Timestamp: The timestamp of the last update to the record.
Record Version (if available): The version number of the record, if your model has a lock_version column or any other versioning system implemented.

Example Usage

Suppose you have a Post model in your Rails application:

class Post < ApplicationRecord
  # Assume this model has attributes: id, title, body, updated_at
end

You can generate a cache key for a post instance like this:

post = Post.find(1)
cache_key = post.cache_key_with_version
puts cache_key

This will output something like:

"posts/1-20240805123045678"

Benefits

Cache Invalidation: When a record is updated, the cache key changes, automatically invalidating the old cache. This ensures that you always have the most recent version of the data in the cache.
Efficiency: It helps improve cache efficiency by avoiding cache hits on stale data.
Version Control: If your application uses optimistic locking with a lock_version column, the cache key will include this version number, adding an additional layer of cache invalidation based on record version.

Custom Cache Key

You can customize the cache key further by overriding the cache_key_with_version method in your model:

class Post < ApplicationRecord
  def cache_key_with_version
    "#{model_name.cache_key}/#{id}-#{updated_at.to_s(:nsec)}-#{version_number}"
  end

  private

  def version_number
    # Custom logic to determine the version number
    lock_version || 1
  end
end

This customization allows you to include additional logic or attributes to be part of the cache key, making it more specific to your application’s requirements.

The cache_key_with_version method is a powerful tool in Rails for managing cache keys with versioning, providing automatic cache invalidation and ensuring that cached data is always up-to-date. If your models have a lock_version column, this method automatically incorporates it, further enhancing cache consistency.