Cached Resource

An AngularJS module to interact with RESTful server-side data
sources, even when the browser is offline. Uses HTML5
localStorage under the hood. Closely mimics the behavior of
the core ngResource module, which it requires as a dependency.

Features

• Provides a simple abstraction to retrieve and save objects from a RESTful
  server.
• Comes with a set of intelligent defaults that let you get started right away.
• Caches all requests, and returns them immediately from the cache if you
  request them again.
• Remmebers writes to the server, and adds them to the cache too.
• If a write fails, try it again periodically until it succeeds. (This even
  works if you refresh the page in between!)
• If you query for multiple resources in one request, each one is cached
  separately so you can request it from the cache individually, too.
• Works as a drop-in replacement for Angular’s $resource module.

News

It looks like this sort of functionality might be built into the upcoming Angular 2.0.
Check out the design document here.

A simple example

// Register your module with ngCachedResource
angular.module('myApp', ['ngCachedResource']);
// Define a resource
var Article = $cachedResource('article', '/articles/:id', {id: "@id"});
// GET requests:
var a1 = Article.get({id: 1});
a1.$promise.then(function() {
  console.log('From cache:', a1);
});
a1.$httpPromise.then(function() {
  console.log('From server:', a1);
});
// POST/PUT/PATCH/DELETE requests:
var a2 = new Article({id: 2}); // *Note: setting the bound param (`id` in this case) is *required*
a2.title = "This article will be saved eventually...";
a2.body = "Even if the browser is offline right now.";
a2.$save();
a2.$promise.then(function() {
  console.log('Article was successfully saved.');
});

Read the tutorial on the Bites from Good Eggs
blog.

*Note: Internally, $cachedResource keeps track of writes by bound params to ensure that it doesn’t duplicate writes. If your bound param is null (say you’re relying on the server to generate ids), then every write will replace the previous one. To avoid this undesirable scenario, simply ensure the id is set on the client, and you can safely ignore it on the server.

Installing

Bower:

bower install angular-cached-resource

npm: (intended for use with browserify)

npm install angular-cached-resource

Manual Download:

• development: angular-cached-resource.js
• production: angular-cached-resource.min.js

Usage

Provides a factory called $cachedResource:

$cachedResource(cacheKey, url, [paramDefaults], [actions]);

Arguments

• cacheKey, String
  
  An arbitrary key that will uniquely represent this resource in localStorage.
  When the resource is instanciated, it will check localStorage for any

• url, String
  
  Exactly matches the API for the url param of the $resource
  factory.

• paramDefaults, Object, (optional)
  
  Exactly matches the API for the paramDefaults param of the
  $resource factory.

• actions, Object, optional
  
  Mostly matches the API for the actions param of the
  $resource factory. Takes an additonal cache param (Boolean,
  default true) that determines if this action uses caching.

Returns

A CachedResource “class” object. This is a swap-in replacement for an object
created by the $resource factory, with the following additional properties:

• Resource.$clearCache( [options] )
  
  Clears all items from the cache associated with this resource. Accepts one
  argument, described below.

  • options, Object, optional
    
    options may contain the following keys:
    • where, which will limit the resources that are cleared from the cache
      to only those whose keys are explicitly listed. where can be an Array
      or an Object. If it is an Object, it will be treated like an Array
      containing only the provided Object. The Array should contain Objects
      representing cache keys that should be removed. If where is provided,
      exceptFor must not be provided.
    • exceptFor, which will limit the resources that are cleared from the
      cache to all resources except for those whose keys are explicitly listed.
      Just like where, exceptFor can be an Array or an Object. If it is an
      Object, it will be treated like an Array containing only the provided
      Object. The Array should contain Objects representing cache keys that
      should be kept. If exceptFor is provided, where must not be provided.
    • isArray, a boolean. Default is false. If true, then the function will
      treat the where or exceptFor arguments as referring to Array cache key.
    • clearChildren, a boolean. Default is false. If true, and isArray is
      also true, then the function will clear the Array cache entry (or entries)
      as well as all of the instances that the Array points to.
    • clearPendingWrites, a boolean. Default is false. If true, then
      the function will also remove cached instances that have a pending
      write to the server.

In addition, the following properties exist on CachedResource “instance” objects:

• resource.$promise
  
  For GET requests, if anything was already in the cache, this
  promise is immediately resolved (still asynchronously!) even as the HTTP request
  continues. Otherwise, this promise is resolved when the HTTP request responds.

• resource.$httpPromise
  
  For all requests, this promise is resolved as soon as the
  corresponding HTTP request responds.

Clearing the cache

Since there is a 5 megabyte limit on localStorage in most browsers, you’ll
probably want to actively manage the resource instances that are stored. By
default, this module never removes cache entries, so you’ll have to do this by
hand. Here are the ways that you can accomplish this:

• localStorage.clear()
  
  Removes everything in localStorage. This will not break the behavior of
  this module, except that it will prevent any pending write from actually
  occurring.

• $cachedResource.clearCache()
  
  Removes every single Angular Cached Resource cache entry that’s currently
  stored in localStorage. It will leave all cache entries that were not created
  by this module. (Note: cache entries are namespaced, so if you add anything
  to localStorage with a key that begins with cachedResource://, it will get
  deleted by this call). It will also leave any resource instances that have a
  pending write to the server.

• $cachedResource.clearUndefined()
  
  Removes every Angular Cached Resource cache entry corresponding to a resource
  that has not been defined since the page was loaded. This is useful if your
  API changes and you want to make sure that old entries are cleared away.

• $cachedResource.clearCache({exceptFor: [‘foo’, ‘bar’]})
  
  Removes every Angular Cached Resource entry except for resources with the
  foo or bar keys, or resource instances that have a pending write to the
  server.

• $cachedResource.clearCache({clearPendingWrites: true})
  
  Removes every Angular Cached Resource entry, including those that have a
  pending write to the server.

If you have a “class” object that you’ve created with $cachedResource, then
you can also do the following:

• CachedResource.$clearCache()
  
  Removes all entries from the cache associated with this particular resource
  class, except for resource instances that have a pending write to the server.

• CachedResource.$clearCache({where: [{id: 1}, {id: 2}])
  
  Removes two entries from the cache associated with this particular resource
  class; the ones with an id of 1 and 2. (This assumes that paramDefaults
  has an id param.)

• CachedResource.$clearCache({exceptFor: {id: 1})
  
  Removes all entries from the cache associated with this particular resource
  class, except for those with an id of 1. (This assumes that
  paramDefaults has an id param.)

• CachedResource.$clearCache({exceptFor: {query: ‘search string’}, isArray: true})
  
  Removes all entries from the cache except those that were returned by the
  provided query parameters.

• CachedResource.$clearCache({clearPendingWrites: true})
  
  Removes all instances of CachedResource from the cache, including those that
  have a pending write to the server.

Details

Asking for a cached resource with get or query will do the following:

1. If the request has not been made previously, it will immediately return a
   resource object, just like usual. The request will go through to the
   server, and when the server responds, the resource will be saved in a
   localStorage cache.

2. If the request has already been made, it will immediately return a
   resource object that is pre-populated from the cache. The request will
   still attempt to go through to the server, and if the server responds, the
   cache entry will be updated.

Updating a CachedResource object will do the following:

1. Add the resource update action to a queue.
2. Immediately attempt to flush the queue by sending all the network requests
   in the queue.
3. If a queued network request succeeds, remove it from the queue and resolve
   the promises on the associated resources (only if the queue entry was made
   after the page was loaded)
4. If the queue contains requests, attempt to flush it once per minute OR
   whenever the browser sends a navigator.onOnline event.

What if localStorage doesn’t exist, or if the browser is out of space?

In either of these cases, $cachedResource will make sure all of your requests
still happen. Things end up working just like the $resource module, with
none of the caching benefits.

Development

Please make sure you run the tests, and add to them unless it’s a trivial
change. Here is how you can run the tests:

npm install
npm test

License

MIT