livelystream

Stream changes to and from a lively dataase as a node.js stream.

Installation

This module is installed via npm:

$ npm install livelystream

Example Usage

LivelyStream when used in conjunction with ObserveStream will replicate data from the database pointed to LivelyStream with the local javascript object pointed to by ObserveStream:

// a database to replicate to/from
var memdb = new MemLively();
 
// bind the database to the lively stream
var ls = new LivelyStream(memdb);
 
// scope will contain the local javascript versions of the data in the database
var scope = {};
 
// Watch for any changes on scope.target and replicate to the 'eugene' key in
// the remote database
var os = new ObserveStream('eugene', scope, 'target', {});
 
// Connect the database to the observestream to do two-way replication
ls.pipe(os).pipe(ls);
 
// Making any changes to the database, should eventually replicate
// the changes to scope.target
memdb.put('eugene', { name: 'Eugene', number: 42 }, function () {});
 
// Making any changes to the local scope.target will replicate to he database
scope.target.name = 'Susan';

API

LivelyStream(db)

Constructs a new LivelyStream instance bound to a Lively database.

• db - the Lively database to synchronize to. (eg. MemLively

Outbound 'data' Events emitted by LivelyStream

The LivelyStream emits 'data' events with the following format:

Initial value events

The very first event that the LivelyStream fires will be the value event. This will contain the inital value of the key in the database, or if the key is not found in the database, then the initialValue will be returned.

For example, if the initial value in the database is my value then the first event emitted would be:

['value', 'my value']

change events

Any time there is a change in the database, a change event is emitted. The change is in changeset object diff format. For example:

['change', [
    { type: 'put', key: ['name'], value: 'Eugene' },
    { type: 'put', key: ['number'], value: 42 },
    { type: 'del', key: ['old'] } ] ]

Inbound events consumed by LivelyStream to change database values

listen event

The very first event that should be received to synchronization should be a listen event, which contains a key and an initialValue.

A sample message is:

['listen', { key: 'my key', initialValue: {} }]

• key - The key to bind to the remote database for watching.
• initialValue - If there is nothing in the database at the key then use this as the initial value.

change events

When piped from a stream such as ObserveStream, the inbound stream can write events that can modify the underlying database values pointed to by the key.

The format of these events is the same as the change event listed above.

Eg:

['change', [
    { type: 'put', key: ['name'], value: 'Eugene' },
    { type: 'put', key: ['number'], value: 42 },
    { type: 'del', key: ['old'] } ] ]