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

`` js
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

` js
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.

[leveldb]: https://github.com/Level/level

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