cocache

cocache

Cocache is a library for caching objects in memory with special semantics for dealing with collections of records.

Installation

Pull it down from npm:

npm install --save cocache

You need an ES6 transpiler to use the module. Assuming you got that set-up, simply require cocache and build your hot new cache instance:

const Cocache = require('cocache');
const myCache = Cocache();

API

Go Cocache here.

Domain Collections

In Cocache, records may be referenced individually or through domain collections - a collection can be thought of like a database view in that it defines the domain in which a certain set of records are relevant.

For example, in a Twitter-like application, a collection could be defined for a list of user objects that are following a specific user, in which case the collection is the list of people, the records are the user objects, and the domain (its id) is the user being followed.

cache.add({ id: '1', name: 'Alice' });
cache.add({ id: '2', name: 'Bob' });

cache.addToCollection('FOLLOWERS_OF_BOB', [{ id: '1' }]); // Alice
cache.getCollection('FOLLOWERS_OF_BOB'); // [{ id: '1', name: 'Alice' }]

Object canonicalization

Cocache expects every individual record to be unique. When a collection is defined, it is managed internally as a shallow list; a list of references to records. Any mutative operation that produces a change in a certain record will be reflected everywhere.

This semantic ensures that a record, mapped to an id, is always guaranteed to have the same representation - regardless of the source it was pulled from (i.e. cache.get() vs cache.getCollection()) and regardless of the operation that affected it (e.g. cache.add(), cache.addToCollection, etc.).

Here's a brief snippet that shows the implication of this:

cache.add({ id: '1' });
cache.get('1');
// => { id: '1' }

cache.addToCollection({ projectId: '1' }, [{ id: '1', title: 'foo' }]);
cache.get('1');
// => { id: '1', title: 'foo' }

cache.getCollection({ projectId: '1' });
// => [{ id: '1', title: 'foo' }]

Object integrity enforcement

It is usually a good idea to validate what goes inside a storage layer like Cocache. To that end, Cocache provides you with a hook to validate each record that is going into the cache.

So long as each record yields a unique identifier, Cocache tries to make as few assumptions as possible about the shape of the data you're shoving into it and delegates the responsibility of validating the structure to the application layer.

To define a custom validation routine, pass in a list of functions to the constructor under recordValidators.

Here's an example that requires each record to contain an "id" string property:

const Cocache = require('cocache');
const cache = Cocache({
  recordValidators: [
    function(record, options, displayName) {
      if (typeof record.id !== 'string') {
        throw new Error(`
          Expected record to contain a string 'id' property.
          Source: Cocache[${displayName}]`
        );
      }
    }
  ]
});

A more sophisticated solution could be achieved by utilizing a strong-schema validator module, such a React's PropTypes or react- schema. The options passed to the cache are also passed to your validator, utilize them!

See ../cocache-schema/README.md for adding a React PropTypes-based structural validation layer to your cocaches.

Content-change signals

Anytime the cache contents change, Cocache is able to emit a signal so that you may render a UI or re-do anything that relies on the cache contents.

const Cocache = require('cocache');
const cache = Cocache(function onChange() {
  console.log('cache contents have changed!');
});

High-resolution change signals

A cache instance accepts an optimized: Boolean option, which is on by default, that allows it to perform deep equality checks between records, resulting in accurate change signals.

These checks are done using Immutable.JS and work great on objects that have no custom prototypes.

This may become a costly operation if the records you're storing are structurally complex, in which case I'd recommend to turn this off.

You should also turn it off if you don't really care about noise-signal ratio (e.g. the change listeners are really cheap).

Transactional operations

Cocache allows you to travel back in time (heh) and restore it to a previous state. This comes in handy when you want to optimistically apply the effects of an operation that may or may not be rejected in the future (like a Promise or an API call response.)

See Cocache#transaction and Cocache#rollback for more information.

Below is an example of updating a user's name immediately and restoring it in case the API refuses to update that record:

cache.transaction(function() {
  cache.add({ id: '1', name: 'Bongo' });

  return ajax({
    type: 'PATCH',
    url: '/users/1',
    data: { name: 'Bongo' }
  });
});

If the Promise yielded by ajax rejects, the cache's representation of the record "1" will be restored to what it was prior to making that add call.

Record expiry & TTL

TODO: not implemented yet

License

Cocache - Collection-aware memory storage. Copyright (C) 2016-2017 Instructure, INC.

This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License along with this program. If not, see http://www.gnu.org/licenses/.