contextdb

Use json-context with leveldb. Contexts are automatically generated from matchers, and provides ability to watch matchers for realtime notifications.

ContextDB - JSON Context for LevelDB

This module creates instances of JsonContext from a leveldb database using levelup. Datasources are automatically generated from matchers and watch for realtime changes.

$ npm install contextdb

Pass in an instance of a levelup database and specify matchers. Ensure the database has encoding: 'json'. Returns an instance of contextDB

Options:

  • matchers: Route changes into the correct places, and provide building blocks for page contexts. In addition to the matcher options on JSON Context, you need to specify matcher.ref as well. Use ref to refer to this matcher later when building contexts. Placeholders can be specified anywhere in the matcher filter by using {$param: 'queryToGetData'}
  • primaryKey: Choose the object key to use as the primary index. Defaults to 'id'.
  • incrementingKey: (defaults to '_seq') Add an incrementing ID to objects
  • timestamps: (defaults to true) whether to automatically add timestamps to edited objects created_at, updated_at, deleted_at. Required if using datasource.emitChangesSince.
var LevelDB = require('levelup')
var ContextDB = require('contextdb')
 
var db = LevelDB(__dirname + '/test-db', {
  encoding: 'json'
})
 
var contextDB = ContextDB(db, {
  matchers: [
    { ref: 'items_for_parent',
      item: 'items[id={.id}]',
      collection: 'items',
      match: {
        parent_id: {$param: 'parent_id'},
        type: 'comment'
      },
      allow: {
        change: true
      }
    },
    { ref: 'current_user',
      item: 'user',
      match: {
        type: 'user',
        id: 'user_123'
      }
    }
  ],
  primaryKey: 'id'
})

Push objects into the database. This will also notify all relevant datasources listening.

All changes will be accepted so this should only be triggered by trusted sources.

var newObject = {
  id: 1,
  parent_id: 'site',
  name: "Home",
  type: 'page'
}
 
contextDB.applyChange(newObject)

Returns a datasource (instance of JSON Context) prepopulated with the relevent data as chosen by matchers and starting data.

It will recieve live events from the database for all specified matchers until datasource.destroy() is called.

Changes pushed in using datasource.pushChange will be checked against matchers and if pass, applied to the database.

Options:

  • data: The starting point for the datasource. Matchers can use $query to hook into the specified attributes.
  • matcherRefs: An array of refs from the matchers specified when creating the contextDB. This option is order sensitive as matchers can refer to the result of another matcher.

Will cause the datasource to emit all changes to any listeners that have occured since the given timestamp (including deletions)

var params = {parent_id: 1, user_id: 'user_123', token: 'some_unique_random_string'}
var matcherRefs = ['current_user', 'items_for_parent']
 
var userDatasources = {}
 
contextDB.generate(params, matcherRefs, function(errdatasource){
 
  // save the context for connecting to later 
  // in production we'd want to auto destroy if no connection recieved 
  userDatasources[params.token] = datasource
 
  // using realtime-templates 
  renderer.render('page', datasource, function(errhtml){
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.end(html)
  })
})

And handle the realtime connections:

var Shoe = require('shoe')
 
Shoe(function (stream) {
  var datasource = null
 
  stream.once('data', function(data){
    var token = data.toString().trim()
    datasource = userDatasources[token]
    console.log('LOGGING IN:', token)
    if (datasource){
      stream.pipe(datasource.changeStream()).pipe(stream)
    } else {
      stream.close()
    }
  })
 
  stream.once('end', function () {
    if (datasource){
      console.log("CLOSING:", datasource.data.token)
      datasource.destroy()
      userDatasources[datasource.data.token] = null
    }
  })
 
}).install(server, '/contexts')

And on the client:

var stream = Shoe('http://localhost:9999/contexts')
stream.write(datasource.data.token + '\n') //log in 
stream.pipe(datasource.changeStream({verifiedChange: true})).pipe(stream)