level-patch-data

Store and read object patches (with metadata) in insert order

Example

var concat = require('concat-stream')
var assert = require('assert')
var level = require('level-test')()
var Patch = require('level-patch-data')

var db = level('patch-test', {valueEncoding: 'json'})
var patch = Patch(db)

patch.add('doc', {a: 'a'}, {user: 'lee'}, function (err, commit) {
  patch.add('doc', {b: 'c'}, {user: 'kara'}, function (err, commit) {

    patch.readStream('doc').pipe(concat(function (body) {
      // body is
      [ { ts: '2014-06-28T06:05:53.100Z', // timestamp
          patch: { a: 'a' },
          key: 'docÿ2014-06-28T06:05:53.100Z' }, // namespaced and sorted by ts
        { user: 'lee',
          ts: '2014-06-28T06:05:53.113Z',
          patch: { b: 'c' },
          key: 'docÿ2014-06-28T06:05:53.113Z' } ]
    }))
  })
})

See tests for more examples.

Methods

var patch = Patch(db, opts)

• db: an instance of levelup or a sublevel to store patches and data.

• opts.separator: the string to use as a separator for key fields. default: '\xff'

• opts.timestampField: the field to use to store the timestamp. default: ts

• opts.keyField: the field to use to store the key. default: key

• opts.patchField: the field to use to store the patch. default: patch

• opts.key: the function to use to generate each patch's key. Use a custom key to add some entropy if there is a chance you'll have two commits in the same millisecond.

  // default
  opts.key = function (meta, namespace, opts) {
    return [namespace, meta[opts.timestampField]].join(opts.separator)
  }

patch.add(namespace, patch, meta, callback)

alias: addPatch

• namespace: the string to identify this collections of patches. This module is designed for use with patcher patches for a single object per unique namespace
• patch: the object to store as the patch
• meta: key/value pairs to store with this patch. Note: the keys opts.timestampField, opts.keyField, and opts.patchField will be overwritten if set.
• callback: receives two arguments, err which is only set if an error occurs and commit, which is the patch and its metadata exactly as it was saved.

patch.readStream(namespace, since)

aliases: createReadStream, read

Returns a readable stream that emits patches for namespace in insert order.

• namespace: the collection of patches to read. patches will be streamed in the order inserted.
• since: optional. pass the key of the commit to read commits since. The commit with key === since will not be returned, only all commits after it.

License

MIT