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level-patch-data

level-patch-data build status

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

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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