MiniCache

MiniCache is a lightweight in-memory key-value store for Ruby objects. This gem requires Ruby version 2.3.0 or higher.

Motivation

It is common practice to cache certain values on an object that are computationally expensive to obtain, such as a property that requires a database query.

The simplest way to do this is by storing the value in an instance variable:

class Account
  def calculate_balance
    # Do something expensive.
  end

  def balance
    @balance ||= self.calculate_balance
  end
end

While this method works in many scenarios, it fails when the value you need to cache is:

Either nil or false
Dependent on a particular argument passed to the method

Here's a demonstration of how MiniCache solves this problem:

class Account
  def lookup_role(user)
    # Execute a database query to find the user's role.
  end

  def role(user)
    # Perform the lookup once and cache the value. We can't use
    #
    #   @role ||= lookup_user(user)
    #
    # because the value depends on the user argument. Also, the
    # value could be nil if the user does not actually have a role.
    # You can probably see how the solution could get pretty ugly.
    # This is where MiniCache comes into play.
    self.cache.get_or_set("role-#{user.id}") do
      self.lookup_role(user)
    end
  end

  def cache
    @cache ||= MiniCache::Store.new
  end
end

The #get_or_set method works similarly to the ||= operator, except it knows how to handle false and nil values and it's keyed off of a unique string ID. Problem solved!

Installation

Add this line to your application's Gemfile:

gem 'mini_cache'

And then execute:

$ bundle

Or install it yourself as:

$ gem install mini_cache

Usage

To create a new MiniCache store object, just initialize it:

store = MiniCache::Store.new

# Optionally pass in a Hash of data
store = MiniCache::Store.new(name: 'Derrick', occupation: 'Developer')

Set and retrieve data using #get and #set:

# Pass in the value as an argument or block
store.set('age', 24)
store.set('birth_year') { 1988 }

store.get('age')
# => 24

store.get('birth_year')
# => 1988

# Sets an expiration time to cache (in seconds)
store.set('age', 24, expires_in: 60)
store.set('day', expires_in: 60) { 12 }
store.set('birth_year') { MiniCache::Data.new(1988, 60) }

store.get('age')
# => 24

store.get('day')
# => 12

store.get('birth_year')
# => 1988

sleep(60)

store.get('age')
# => nil

store.get('day')
# => nil

store.get('birth_year')
#=> nil

Use the #get_or_set method to either set the value if it hasn't already been set, or get the value that was already set.

store.set('birth_year') { 1988 }
#=> 1988

store.get_or_set('birth_year') { 1964 }
#=> 1988  # Did not overwrite previously set value

# You may also set an expiration time (in seconds):

store.get_or_set('age', expires_in: 60) { 24 }
#=> 24

store.get_or_set('birth_year') do
  MiniCache::Data.new(1988, expires_in: 60)
end
#=> 1988

sleep(60)

store.get_or_set('age', expires_in: 60) { 28 }
#=> 28

store.get_or_set('birth_year') do
  MiniCache::Data.new(1964, expires_in: 60)
end
#=> 1964

Other convenience methods:

#set?(key): Checks to see if a value has been set for a given key
#unset(key): Removes a key-value pair for a given key.
#reset: Clears the cache.
#load(hash): Loads a hash of data into the cache (appended to existing data).

Contributing

Fork it
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Added some feature')
Push to the branch (git push origin my-new-feature)
Create new Pull Request