@mapeo/realm-indexer

⚠️ This is an Alpha release and the API might change. Do not use in production. ⚠️

Index Mapeo data in a Realm database

Mapeo data is stored in multiple append-only logs (we use Hypercore). The data is structured as a Directed Acylclic Graph (DAG) for each document id: each edit of a particular document is stored as a new document that points to its "parent". This can result in "forks": the same parent can be edited in two different instances of Mapeo, resulting in two versions of the same document.

This indexer accepts batches of Mapeo documents of a particular type (namespace) and indexes the "head" document. If a document is forked then a "winner" is chosen deterministically, either by a timestamp or by comparing version ids. The documents heads are stored in a Realm database, so that further querying and indexing of the documents is done within Realm.

Any document that is indexed must have the following type:

type IndexableDocument = {
  id: string
  version: string
  links: string[]
  timestamp?: string | number
}

The Realm database used as the index must also contain an object schema for storing these documents which must at a minimum include:

const DocSchema = {
  name: 'Doc',
  properties: {
    id: 'string',
    version: 'string',
    links: 'string[]',
    forks: {
      type: 'set',
      objectType: 'string',
    },
  },
  primaryKey: 'id',
}

Table of Contents

• Install
• Usage
• API
• Maintainers
• Contributing
• License

Install

npm install @mapeo/realm-indexer

Usage

import Realm from 'realm'
import RealmIndexer from './index.js'

const realm = new Realm({
  schema: [RealmIndexer.DocSchema, RealmIndexer.BacklinkSchema],
})

const docs = [
  { id: 'A', version: '1', links: [] },
  { id: 'A', version: '2', links: ['1'] },
  { id: 'A', version: '3', links: ['1'] },
  { id: 'A', version: '4', links: ['2', '3'] },
]

const indexer = new RealmIndexer(realm, {
  docType: RealmIndexer.DocSchema.name,
  backlinkType: RealmIndexer.BacklinkSchema.name,
})

indexer.batch(docs)

const A = realm.objectForPrimaryKey('Doc', 'A')
// { id: 'A', version: '4', links: ['2', '3'], forks: [] }

API

const indexer = new RealmIndexer(realm, opts)

realm

Required
Type: Realm

An instance of a Realm database.

opts

Required
Type: object

opts.docType

Required
Type: string

The name of the Realm schema for storing the indexed documents.

opts.backlinkType

Required
Type: string

The name of the Realm schema for storing backlinks (used internally for indexing). Must have the schema:

const BacklinkSchema = {
  name: 'Backlink',
  properties: {
    version: 'string',
  },
  primaryKey: 'version',
}

indexer.batch(docs)

Index an array of documents. Documents can be in any order. Documents must have an id property, a version property that is unique, and a links property which is an array of version ids for the documents parent(s).

docs

Requires
Type: Array<{ id: string, version: string, links: string[] }>

Additional properties will be ignored but included in the Realm index. They should also be defined in the DocSchema and match the type. The document stored in Realm will have a forks property which is an array of version ids for other forks of the document id, if forks exist.

Maintainers

@digidem

Contributing

PRs accepted.

Small note: If editing the README, please conform to the standard-readme specification.

License

MIT © 2022 Digital Democracy