unordered-materialized-backrefs

materialized view to calculate back-references for unordered log messages

Use this library as a materialized view to track back-references for append-only log data which can be inserted in any order. Back-references let you query for which set of documents points at another document.

example

var umbr = require('unordered-materialized-backrefs')
var db = require('level')('/tmp/br.db')
var br = umbr(db)
 
if (process.argv[2] === 'insert') {
  var doc = JSON.parse(process.argv[3])
  br.batch([doc], function (err) {
    if (err) console.error(err)
  })
} else if (process.argv[2] === 'get') {
  var key = process.argv[3]
  br.get(key, function (err, ids) {
    if (err) console.error(err)
    else console.log(ids)
  })
}

you can insert documents and query which documents link to which other documents:

$ rm -rf /tmp/br.db \
&& node refs.js insert '{"id":"a","refs":[]}' \
&& node refs.js insert '{"id":"b","refs":["a"]}' \
&& node refs.js insert '{"id":"c","refs":["a"]}'
$ node refs.js get a
[ 'b', 'c' ]

the linked-to documents need not exist:

$ rm -rf /tmp/br.db \
&& node refs.js insert '{"id":"b","refs":["a"]}' \
&& node refs.js insert '{"id":"c","refs":["a"]}'
$ node refs.js get a
[ 'b', 'c' ]

linking replaces refs:

$ rm -rf /tmp/br.db \
&& node refs.js insert '{"id":"a","refs":[]}' \
&& node refs.js insert '{"id":"b","refs":["a"]}' \
&& node refs.js insert '{"id":"c","refs":["a"]}' \
&& node refs.js insert '{"id":"d","refs":["a"],"links":["c"]}'
$ node refs.js get a
[ 'b', 'd' ]

when you replace a document by linking, you remove its refs:

$ rm -rf /tmp/br.db \
&& node refs.js insert '{"id":"a","refs":[]}' \
&& node refs.js insert '{"id":"b","refs":[]}' \
&& node refs.js insert '{"id":"c","refs":["a"]}' \
&& node refs.js insert '{"id":"d","refs":["a"]}' \
&& node refs.js insert '{"id":"e","refs":["b"],"links":["d"]}'
$ node refs.js get a
[ 'c' ]
$ node refs.js get b
[ 'e' ]

documents can be inserted in any order:

$ rm -rf /tmp/br.db \
&& node refs.js insert '{"id":"a","refs":[]}' \
&& node refs.js insert '{"id":"b","refs":[]}' \
&& node refs.js insert '{"id":"c","refs":["a"]}' \
&& node refs.js insert '{"id":"d","refs":["a"]}' \
&& node refs.js insert '{"id":"e","refs":["b"],"links":["d"]}'
$ node refs.js get a
[ 'c' ]
$ node refs.js get b
[ 'e' ]

api

var umbr = require('unordered-materialized-backrefs')

var br = umbr(db, opts)

Create a br instance from a leveldb instance db (levelup or leveldown).

Only the db.batch() and db.get() interfaces of leveldb are used with no custom value encoding, so you can use any interface that supports these methods.

br.batch(rows, cb)

Write an array of rows into the kv. Each row in the rows array has:

• row.id - unique id string of this record
• row.refs - array of string ids that the current id links to
• row.links - array of id string ancestor links

br.get(id, cb)

Lookup the ids that link to the given id as cb(err, ids).

license

BSD