Plugin to add persistence and querying [scuttlebutt](https://github.com/scuttlebutt) documents stored in leveldb.
npm install level-scuttlebuttPlugin to add persistence and querying scuttlebutt documents
stored in leveldb.
Instead of representing an object as a single document, scuttlebutt represents a document as
a series of immutable transactions. The 'document' is modified by appending a new transaction.
Old transactions that are no longer relevant can be cleaned up, but you can never modify a
transaction in place. As it turns out, leveldb (a log-structured merge tree) is optimized for
exactly this sort of data.
Must be used with level-sublevel
`` js
var levelup = require("levelup")
var level_scuttlebutt = require("level-scuttlebutt")
var SubLevel = require('level-sublevel')
//create a leveldb instance...
//levelup must be extended with SubLevel!
var db = SubLevel(levelup(DB_FILE))
//a scuttlebutt model.
var Model = require('scuttlebutt/model')
//level-scuttlebutt needs to have an unique identifier of the current instance
var udid = require('udid')('app-name')
//patch it with level-scuttlebutt.
var sbDb = db.sublevel('scuttlebutt') //add a scuttlebutt 'table'
//k
level_scuttlebutt(sbDb, udid, function (name) {
//create a scuttlebutt instance given a name.
//the key will match the start of the name.
return new Model()
//now is a good time to customize the scuttlebutt instance.
})
//open a scuttlebutt instance by name.
sbDb.open(name, function (err, model) {
model.on('change:key', console.log) //...
model.set('key', value)
// when you're done get rid of it
model.dispose()
})
//the toJSON values are stored in the db,
//so you can just use any other map reduce library on it!
sbDb.views['all'] =
mapReduce(sbDb, 'all',
function (key, json, emit) {
return emit(key.split('!'), 1)
},
function (acc, item) {
return '' + (Number(acc) + Number(item))
},
'0'
)
`
Add level-scuttlebutt plugin to the db objectvar level_scuttlebutt = require('level-scuttlebutt'); level_scuttlebutt(db, ID, schema)
ID is a unique string that identifies the node (the machine) and should be
tied to the leveldb instance.
I suggest using udid.
schema should be a function that takes a string (the name of the scuttlebutt instance)
and returns and empty scuttlebutt instance.
You can use scuttlebutt-schema.
Use some other level-* plugin for queries!
get the 10 last edited documents!
` js``
sbDb.views['latest10']
=
MapReduce(sdb, 'latest10',
function (key, json) {
var name = key
var obj = JSON.parse(json)
//emit 0-many group-value pairs.
//value must be a string or a buffer.
this.emit([], JSON.stringify({name: name, time: Date.now(), length: obj.text.length}))
},
//merge the latest value into the accumulator.
function (acc, value) {
var all = JSON.parse(acc).concat(JSON.parse(value))
//sort by time, decending.
all.sort(function (a, b) {
return b.time - a.time
})
//top ten most recent
var all = all.slice(0, 10)
return JSON.stringify(all)
},
//the first value for the accumulator.
//since we are parsing it, it needs to be valid JSON.
'[]'
})
MIT