group and reduce rows for foreign key relations for sorted key-value stores like leveldb
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foreign-key

generate keys for sorted key-value stores to group and reduce rows by a foreign key

build status

example

Given some data about hackerspaces, hackers, and items:

[
  { "type": "hackerspace", "name": "sudoroom" },
  { "type": "hacker", "name": "substack", "space": "sudoroom"},
  { "type": "hackerspace", "name": "noisebridge" },
  { "type": "hacker", "name": "mitch", "space": "nosiebridge" },
  { "type": "item", "name": "3d printer", "space": "sudoroom" },
  { "type": "item", "name": "piano", "space": "sudoroom" },
  { "type": "hacker", "name": "mk30", "space": "sudoroom" },
  { "type": "hacker", "name": "rwolfe", "space": "i3" },
  { "type": "item", "name": "3d printer", "space": "noisebridge" },
  { "type": "hacker", "name": "ioerror", "space": "noisebridge" },
  { "type": "hacker", "name": "wrought", "space": "sudoroom" },
  { "type": "hacker", "name": "nbritsky", "space": "i3" },
  { "type": "item", "name": "laser cutter", "space": "noisebridge" },
  { "type": "hackerspace", "name": "i3" }
]

we can generate key names to efficiently group hackers and items with their hackerspace using "space" as a foreign key refering to the "name" of a hackerspace:

var through = require('through');
var foreign = require('foreign-key');

var g = foreign([ 'type', 'hackerspace' ]);
g.add('hackers', [ 'type', 'hacker' ], 'space');
g.add('equipment', [ 'type', 'item' ], 'space');

var db = require('level')('/tmp/foreign-test', { valueEncoding: 'json' });
db.batch(require('./hackers.json').map(function (row) {
    return { type: 'put', key: g.key(row.name, row), value: row };
}));

db.createReadStream()
    .pipe(g.createStream())
    .pipe(through(console.log))
;

output:

{ type: 'hackerspace',
  name: 'i3',
  hackers: 
   [ { type: 'hacker', name: 'nbritsky', space: 'i3' },
     { type: 'hacker', name: 'rwolfe', space: 'i3' } ] }
{ type: 'hackerspace',
  name: 'noisebridge',
  equipment: 
   [ { type: 'item', name: '3d printer', space: 'noisebridge' },
     { type: 'item', name: 'laser cutter', space: 'noisebridge' } ],
  hackers: 
   [ { type: 'hacker', name: 'ioerror', space: 'noisebridge' },
     { type: 'hacker', name: 'mitch', space: 'nosiebridge' } ] }
{ type: 'hackerspace',
  name: 'sudoroom',
  equipment: 
   [ { type: 'item', name: '3d printer', space: 'sudoroom' },
     { type: 'item', name: 'piano', space: 'sudoroom' } ],
  hackers: 
   [ { type: 'hacker', name: 'mk30', space: 'sudoroom' },
     { type: 'hacker', name: 'substack', space: 'sudoroom' },
     { type: 'hacker', name: 'wrought', space: 'sudoroom' } ] }

methods

var foreign = require('foreign-key')

var g = foreign(primaryFilter)

Create a new foreign key instance g that pivots on the rows matching primaryFilter.

g.add(targetKey, filter, foreignKey)

Insert rows matching filter into rows matching primaryFilter at the location into primary rows targetKey.

g.key(key, row)

Return the new key to use for the ordinary unique identifier key given the foreign key rules applicable to row.

g.keyList(key, row)

Return the array of elements that g.key() passes to bytewise.encode().

g.createStream()

Create a through stream that takes row objects as input and combines results from added secondary rows into primary rows.

install

With npm do:

npm install foreign-key

license

MIT