# apostrophe-caches

# Inherits from: apostrophe-module

# apos.caches

A general purpose cache implementation for improved performance in all areas where results can be retained and reused temporarily. Any number of distinct cache objects can be created, identified by distinct names. The standard implementation is powered by a MongoDB collection, however it is straightforward to extend this module with a different implementation for some or all caches by overriding its get method.

# Methods

# get(name)


THIS IS NOT THE METHOD YOU CALL TO GET A VALUE - THIS IS THE METHOD YOU CALL TO GET A CACHE IN WHICH YOU CAN GET AND SET VALUES. Call it with a name that uniquely identifies your entire cache, like weather-data or similar. The object it returns has get and set methods for actual data, as described below.

get('cachename') returns a cache object to store things in temporarily. If you call get many times with the same cache name, you get the same cache object each time.

CACHES MUST NEVER BE RELIED UPON TO STORE INFORMATION. They are a performance enhancement ONLY and data may DISAPPEAR at any time.

HOW TO ACTUALLY CACHE DATA: Every cache object has .get(key, callback) and .set(key, value, lifetime, callback) methods to get and store values in the cache. If you call without a callback, a promise is returned.

Example (with promises):

// Get a cache for weather data, keyed by zip code
var myCache = self.apos.caches.get('weather-data');

// Store something in the cache
myCache.set('19147', { clouds: 'cumulus' }, 86400).then(function() { ... })

// Get a value from the cache
myCache.get('19147').then(function(data) { ... })

The data to be stored must be representable as JSON for compatibility with different implementations. You do NOT have to stringify it yourself.

The .get method of each cache object invokes its callback with (null, value) in the event of success. If the key does not exist in the cache, value is undefined. This is not considered an error. If there is no callback a promise is returned, which resolves to the cached value or undefined.

The lifetime argument of .set is in seconds and may be omitted entirely, in which case data is kept indefinitely (but NOT forever, remember that caches can be erased at ANY time, they are not for permanent data storage).

The default implementation is a single MongoDB collection with a name property to keep the caches separate, but this can be swapped out by overriding the get method.

Caches also have a clear() method to clear the cache. If no callback is passed, it returns a promise.

CACHES MUST NEVER BE RELIED UPON TO STORE INFORMATION. They are a performance enhancement ONLY and data may DISAPPEAR at any time.

# constructCache(name)

# getCollection(callback)

# ensureIndexes(callback)

# clearCacheTask(argv, callback)

# addClearCacheTask()