Caché

A key/value store where pairs can expire after a specified interval

Installation

Add this to your application's shard.yml:

dependencies:
  cache:
    github: crystal-cache/cache

Example

Caching means to store content generated during the request-response cycle and to reuse it when responding to similar requests.

The first time the result is returned from the query it is stored in the query cache (in memory) and the second time it's pulled from memory.

Memory cache can store any serializable Crystal objects.

Next example show how to get a single Github user and cache the result in memory.

require "http/client"
require "json"
require "cache"

cache = Cache::MemoryStore(String, String).new(expires_in: 30.minutes)
github_client = HTTP::Client.new(URI.parse("https://api.github.com"))

# Define how an object is mapped to JSON.
class User
  include JSON::Serializable

  property login : String
  property id : Int32
end

username = "crystal-lang"

# First request.
# Getting data from Github and write it to cache.
user_json = cache.fetch("user_#{username}") do
  response = github_client.get("/users/#{username}")
  User.from_json(response.body).to_json
end

user = User.from_json(user_json)
user.id # => 6539796

# Second request.
# Getting data from cache.
user_json = cache.fetch("user_#{username}") do
  response = github_client.get("/users/#{username}")
  User.from_json(response.body).to_json
end

user = User.from_json(user_json)
user.id # => 6539796

Usage

Available stores

• Null store
• Memory
• Filesystem

There are multiple cache store implementations, each having its own additional features. See the classes under the /src/cache/stores directory, e.g.

Third-party store implementations

• redis_cache_store
• redis_legacy_cache_store
• mem_cache_store
• postgres_cache_store
• mysql_cache_store

Commands

All store's implementations should support:

• fetch
• write
• read
• delete
• clear

fetch

Fetches data from the cache, using the given key. If there is data in the cache with the given key, then that data is returned.

If there is no such data in the cache, then a block will be passed the key and executed in the event of a cache miss.

Setting :expires_in will set an expiration time on the cache. All caches support auto-expiring content after a specified number of seconds. This value can be specified as an option to the constructor (in which case all entries will be affected), or it can be supplied to the fetch or write method to effect just one entry.

write

Writes the value to the cache, with the key.

Optional expires_in will set an expiration time on the key.

Options are passed to the underlying cache implementation.

store = Cache::MemoryStore(String, String).new(12.hours)

store.write("foo", "bar")

read

Reads data from the cache, using the given key.

If there is data in the cache with the given key, then that data is returned. Otherwise, nil is returned.

store = Cache::MemoryStore(String, String).new(12.hours)
store.write("foo", "bar")

store.read("foo") # => "bar"

delete

Deletes an entry in the cache. Returns true if an entry is deleted.

Options are passed to the underlying cache implementation.

store = Cache::MemoryStore(String, String).new(12.hours)

store.write("foo", "bar")
store.read("foo") # => "bar"

store.delete("foo") # => true
store.read("foo") # => nil

clear

Deletes all items from the cache.

Options are passed to the underlying cache implementation.

store = Cache::MemoryStore(String, String).new(12.hours)

store.write("foo", "bar")
store.read("foo") # => "bar"

store.clear
store.read("foo") # => nil

Memory

A cache store implementation which stores everything into memory in the same process.

Can store any serializable Crystal object.

cache = Cache::MemoryStore(String, Hash(String | Int32)).new(expires_in: 1.minute)
cache.fetch("data_key") do
  {"name" => "John", "age" => 18}
end

Cached data for MemoryStore(String, String) are compressed by default. To turn off compression, pass compress: false to the initializer.

For another type of keys compress option ignored.

cache = Cache::MemoryStore(String, String).new(expires_in: 1.minute, compress: false)
cache.fetch("today") do
  Time.utc.day_of_week
end

Filesystem

A cache store implementation which stores everything on the filesystem.

cache_path = "#{__DIR__}/cache"

cache = Cache::FileStore(String, String).new(expires_in: 12.hours, cache_path: cache_path)

cache.fetch("today") do
  Time.utc.day_of_week
end

Null store

A cache store implementation which doesn't actually store anything. Useful in development and test environments where you don't want caching turned on but need to go through the caching interface.

cache = Cache::NullStore(String, String).new(expires_in: 1.minute)
cache.fetch("today") do
  Time.utc.day_of_week
end

Logging

For activation, simply setup the log to :debug level:

Log.builder.bind "cache.*", :debug, Log::IOBackend.new

Contributing

1. Fork it (https://github.com/crystal-cache/cache/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• mamantoha Anton Maminov - creator, maintainer