ActiveModelCachers

Provide cachers to the model so that you could specify which you want to cache. Data will be cached at Rails.cache and also at application level via RequestStore to cache values between requests. Cachers will maintain cached objects and expire them when they are changed (including create, update, destroy, and even delete).

• Multi-level Cache
• Do not pollute original ActiveModel API.
• Support ActiveRecord 3, 4, 5.
• High test coverage

Compare with identity_cache

active_model_cachers allows you to specify what to cache and when to expire those caches. So that you could cache raw sql query results, time-consuming methods, responses of requests, and so on. It also supports AR associations / attibutes (has_many, has_one, belongs_to) and secondary indexes.

identity_cache focuses on AR, and doesn't have the flexibility to specify the query. It has more features for caching AR associations / attibutes, such as caching attibutes by multiple keys, embedding associations to load data in one fetch, non-unique secondary indexes, and caching polymorphic associations, etc.

There is also a difference worths mentioning, active_model_cachers encapsulates methods to cacher, while identity_cache adds a number of fetch_* method to AR directly. Therefore, it's more possible to have method name collision.

Installation

Add this line to your application's Gemfile:

gem 'active_model_cachers'

And then execute:

$ bundle

Or install it yourself as:

$ gem install active_model_cachers

Add an initializer with this code to your project:

ActiveModelCachers.config do |config|
  config.store = Rails.cache # specify where the cache will be stored
end

Usage

Cache whatever you want by cache_at method

cache_at(name, query = nil, options = {})

Specify a cache on the model.

• name: the attribute name.
• query: how to get data on cache miss. It will be set automatically if the name match an association or an attribute.
• options: see here

Asscess the cached attributes

The cacher is defined as class method and instance method of Model. You could call the method and get the cacher instance, e.g. User.cacher or user.cacher. An attribute will define a method on cacher, cached attributes are asscessable via it, e.g. user.cacher.the_attribute_name.

Basic Example

class User < ActiveRecord::Base
  cache_at :something_you_want_to_cache, ->{ get_the_data_on_cache_miss }
end

user.cacher.something_you_want_to_cache

Examples

Example 1: Cache the number of active user

After specifying the name as active_count and how to get data when cache miss by lambda User.active.count. You could access the cached data by calling active_count method on the cacher, User.cacher.

class User < ActiveRecord::Base
  scope :active, ->{ where('last_login_at > ?', 7.days.ago) }
  cache_at :active_count, ->{ active.count }, expire_by: 'User#last_login_at'
end

@count = User.cacher.active_count

You may want to flush cache on the number of active user changed. It can be done by simply setting expire_by. In this case, User#last_login_at means flushing the cache when a user's last_login_at is changed (whenever by save, update, create, destroy or delete).

Example 2: Cache the number of user

In this example, the cache should be cleaned on user destroyed, or new user created, but not on user updated. You could specify the cleaning callback to only fire on certain events by on.

class User < ActiveRecord::Base
  cache_at :count, ->{ count }, expire_by: 'User', on: [:create, :destroy]
end

@count = User.cacher.count

Example 3: Access the cacher from a model instance

You could use the cacher from instance scope, e.g. user.cacher, instead of User.cacher. The difference is that the binding of query lambda is changed. In this example, you could write the query as posts.exists? in that it's in instance scope, and the binding of the lambda is user, not User. So that it accesses posts method of user.

class User < ActiveRecord::Base
  has_many :posts
  cache_at :has_post?, ->{ posts.exists? }, expire_by: :posts
end

do_something if current_user.cacher.has_post?

In this example, the cache should be cleaned when the posts of the user changed. You could just set expire_by to the association: :posts, and then it will do all the works for you magically. (If you want know more details, it actually set expire_by to Post#user_id and foreign_key, which is needed for backtracing the user id from post, to :user_id)

Example 4: Pass an argument to the query lambda.

You could cache not only the query result of database but also the result of outer service. Becasue email_valid? doesn't match an association or an attribute, by default, the cache will not be cleaned by any changes.

class User < ActiveRecord::Base
  cache_at :email_valid?, ->(email){ ValidEmail2::Address.new(email).valid_mx? }
end

render_error if not User.cacher_at('[email protected]').email_valid?

The query lambda can have one parameter, you could pass variable to it by using cacher_at. For example, User.cacher_at(email).

class User < ActiveRecord::Base
  cache_at :email_valid?, ->(email){ ValidEmail2::Address.new(email).valid_mx? }, primary_key: :email
end

render_error if not current_user.cacher.email_valid?

It can also be accessed from instance cacher. But you have to set primary_key, which is needed to know which attribute should be passed to the parameter.

Example 5: Store all data in hash

Sometimes you may need to query multiple objects. Although the query results will be cached, the application still needs to query the cache server multiple times. If one communication take 0.1 ms, 1000 communications will take 100ms! For example:

class Skill < ActiveRecord::Base
  cache_at :atk_power
end

# This will retrieve the data from cache servers multiple times.
@attack = skill_ids.inject(0){|sum, id| sum + Skill.cacher_at(id).atk_power }

One of the solution is that you could store a lookup table into cache, so that only one cache object is stored and you can retrieve all of the needed data in one query.

class Skill < ActiveRecord::Base
  cache_at :atk_powers, ->{ pluck(:id, :atk_power).to_h }, expire_by: 'Skill#atk_power'
end

# This will retrieve the data from cache servers only 1 times.
@attack = skill_ids.inject(0){|sum, id| sum + Skill.cacher.atk_powers[id] }

Example 6: Clean the cache manually

Sometimes it needs to maintain the cache manually. For example, after calling update_all, delete_all or import records without calling callbacks.

class User < ActiveRecord::Base
  has_one :profile
  cache_at :profile
end

# clean the cache by name
current_user.cacher.clean(:profile)

# or calling the clean_* method
current_user.cacher.clean_profile

# clean the cache without loading model
User.cacher_at(user_id).clean_profile

Example 7: Peek the data stored in cache

If you just want to check the cached objects, but don't want it to load from database automatically when there is no cache. You could use peek method on cacher.

class User < ActiveRecord::Base
  has_one :profile
  cache_at :profile
end

# peek the cache by name
current_user.cacher.peek(:profile)

# or calling the peek_* method
current_user.cacher.peek_profile

# peek the cache without loading model
User.cacher_at(user_id).peek_profile

Smart Caching

Multi-level Cache

There is multi-level cache in order to make the speed of data access go faster.

1. RequestStore
2. Rails.cache
3. Association Cache
4. Database

RequestStore is used to make sure same object will not loaded from cache twice, since the data transfer between Cache and Application still consumes time.

Association Cache will be used to prevent preloaded objects being loaded again.

For example:

user = User.includes(:posts).take
user.cacher.posts # => no query will be made even on cache miss.

Convenient syntax sugar for caching ActiveRecord

Caching Associations

class User < ActiveRecord::Base
  has_one :profile
  cache_at :profile
end

@profile = current_user.cacher.profile

# directly get profile without loading user.
@profile = User.cacher_at(user_id).profile

Caching Self

Cache self by id.

class User < ActiveRecord::Base
  cache_self
end

@user = User.cacher.find_by(id: user_id)

# peek cache
User.cacher.peek_by(id: user_id)

# clean cache
User.cacher.clean_by(id: user_id)

Also support caching self by other columns.

class User < ActiveRecord::Base
  cache_self by: :account
end

@user = User.cacher.find_by(account: 'khiav')

# peek cache
User.cacher.peek_by(account: 'khiav')

# clean cache
User.cacher.clean_by(account: 'khiav')

Caching Attributes

class Profile < ActiveRecord::Base
  cache_at :point
end

@point = Profile.cacher_at(profile_id).point

Options

:expire_by

Monitor on the specific model. Clean the cached objects if target are changed.

• if empty, e.g. nil or '': Monitoring nothing.

• if string, e.g. User: Monitoring all attributes of User.

• if string with keyword #, e.g. User#last_login_in_at: Monitoring only the specific attribute.

• if symbol, e.g. :posts: Monitoring on the association. It will trying to do all the things for you, including monitoring all attributes of Post and set the foreign_key.

• Default value depends on the name. If is an association, monitoring the association klass. If is an attribute, monitoring current klass and the attrribute name. If others, monitoring nothing.

:on

Fire changes only by a certain action with the on option. Like the same option of after_commit.

• if :create: Clean the cache only on new record is created, e.g. Model.create.

• if :update: Clean the cache only on the record is updated, e.g. model.update.

• if :destroy: Clean the cache only on the record id destroyed, e.g. model.destroy, model.delete.

• if array, e.g. [:create, :update]: Clean the cache by any of specified actions.

• Default value is [:create, :update, :destroy]

:foreign_key

This option is needed only for caching assoication and need not to set if expire_by is set to monitor association. Used for backtracing the cache key from cached objects. For examle, if user has_many posts, and cached the posts by user.id. When a post is changed, it needs to know which column to use (in this example, user_id) to clean the cache at user.

• Default value is :id

• Will be automatically determined if expire_by is symbol.

:primary_key

This option is needed to know which attribute should be passed to the parameter when you are using instance cacher. For example, if a query, named email_valid?, uses user.email as parameter, and you call it from instance: user.cacher.email_valid?. You need to tell it to pass user.email instead of user.id as the argument.

• Default value is :id

Future works

• caching polymorphic associations
• non-unique secondary indexes
• caching attibutes by multiple keys
• testing counter cache
• testing has_many through
• testing has_and_belongs_to_many

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test 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.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/khiav223577/active_model_cachers. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

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