Support Table Cache

This gem adds caching for ActiveRecord support table models. These models have a unique key (i.e. a unique name attribute, etc.) and a limited number of entries (a few hundred at most). These are often models added to normalize the data structure and are also known as lookup tables.

Rows from these kinds of tables are rarely inserted, updated, or deleted, but are queried very frequently. To take advantage of this behavior, this gem adds automatic caching for records when using the find_by method and belongs_to associations.

For instance, suppose you have a model Status that has a unique name attribute and you need to process a lot of records from a data source that includes the status name. In order to do anything, you'll need to look up each status by name to get the database id:

params.each do |data|
  status = Status.find_by(name: data[:status]
  Things.where(id: data[:id]).update!(status_id: status.id)
end

With this gem, you can avoid the database query associated with the find_by call. You don't need to alter your code in any way other than to include SupportTableCache in your model and telling it the attributes that comprise a unique key, which can be used for caching.

Usage

To use the gem, you need to include it in you models and then specify which attributes can be used for caching with the cache_by method. A caching attribute must be a unique key on the model. For a composite unique key, you can specify an array of attributes. If any of the attributes are case-insensitive strings, you need to specify that as well.

  class MyModel < ApplicationRecord
    include SupportTableCache

    cache_by :id
    cache_by [:group, :name], case_sensitive: false
  end

  # Uses cache
  MyModel.find_by(id: 1)

  # Uses cache on a composite key
  MyModel.find_by(group: "first", name: "One")

  # Uses cache on a composite key with scoping
  MyModel.where(group: "first").find_by(name: "One")

  # Does not use cache because the value is not defined as a cacheable key
  MyModel.find_by(value: 1)

  # Does not use caching because not using the find_by method
  MyModel.where(id: 1).first

By default, records will be cleaned up from the cache only when they are modified. However, you can change this by setting a time to live on the model after which records will be removed from the cache.

  class MyModel < ApplicationRecord
    include SupportTableCache

    self.support_table_cache_ttl = 5.minutes
  end

Setting the Cache

If you are in a Rails application, the Rails.cache will be used by default to cache records. Otherwise, you need to set the ActiveSupport::Cache::CacheStore instance to use.

SupportTableCache.cache = ActiveSupport::Cache::MemoryStore.new

You can also set a cache per class. For instance, you can set an in-memory cache on models that are never changed to avoid a network round trip to the cache server. You can use the special value :memory to do this.

  class MyModel < ApplicationRecord
    include SupportTableCache

    self.support_table_cache = :memory
  end

Note that in-memory caches exist separately within each process and will not be cleared when records are changed in the database. The only way to refresh elements in an in-memory cache is to restart the process or set the support_table_cache_ttl value so that the entries will expire.

Disabling Caching

You can disable the cache within a block either globally or only for a specific class. If the cache is disabled, then all queries will pass through to the database.

# Disable the cache globally
SupportTableCache.disable

SupportTableCache.enable do
  # Re-enable the cache within a block
  SupportTableCache.disable do
    # Disable it again
    MySupportModel.enable_cache do
      # Re-enable it only for the MySupportModel class
    end
  end
end

Caching Belongs to Associations

You can also cache belongs to associations to cacheable models.

To do this, you include the SupportTableCache::Associations module in your model and then call cache_belongs_to to specify which associations should be cached. You must define the association first with belongs_to before you can call cache_belongs_to. You can include SupportTableCache::Associations in ApplicationRecord if you want this behavior available to all of your models.

The target class for the association must include the SupportTableCache module.

class ParentModel <  ApplicationRecord
  include SupportTableCache::Associations

  belongs_to :my_model
  cache_belongs_to :my_model
end

You can include SupportTableCache::Associations in your ApplicationRecord class to make association caching available on all models.

Testing

Caching may interfere with tests by allowing data created in one test to leak into subsequent tests. You can resolve this by wrapping your tests with the SupportTableCache.testing! method.

# Rspec
RSpec.configure do |config|
  config.around do |example|
    SupportTableCache.testing! { example.run }
  end
end

# MiniTest (with the minitest-around gem)
class MiniTest::Spec
  around do |tests|
    SupportTableCache.testing!(&tests)
  end
=end

Maintaining Data

You can use the companion support_table_data gem to provide functionality for loading static data into your support tables as well as adding helper functions to make looking up specific rows much easier.

Installation

Add this line to your application's Gemfile:

gem "support_table_cache"

Then execute:

$ bundle

Or install it yourself as:

$ gem install support_table_cache

Contributing

Open a pull request on GitHub.

Please use the standardrb syntax and lint your code with standardrb --fix before submitting.

License

The gem is available as open source under the terms of the MIT License.

bdurand/support_table_cache