Neoanthropic Preternatural Murmurings
    Wondering what’s next for npm?Check out our public roadmap! »

    subleveldown
    DefinitelyTyped icon, indicating that this package has TypeScript declarations provided by the separate @types/subleveldown package

    5.0.1 • Public • Published

    subleveldown

    Split a levelup database into sublevels with their own keyspace, encoding and events.

    level badge npm Node version Travis npm Coverage Status JavaScript Style Guide Backers on Open Collective Sponsors on Open Collective

    Table of Contents

    Click to expand

    Usage

    If you are upgrading: please see UPGRADING.md.

    var sub = require('subleveldown')
    var level = require('level')
     
    var db = level('db')
    var example = sub(db, 'example')
    var nested = sub(example, 'nested')

    The example and nested db's are just regular levelup instances:

    example.put('hello', 'world', function () {
      nested.put('hi', 'welt', function () {
        // will print {key:'hello', value:'world'}
        example.createReadStream().on('data', console.log)
      })
    })

    They also support db.clear() which is very useful to empty a bucket of stuff:

    example.clear(function (err) {})
     
    // Or delete a range within `example`
    example.clear({ gt: 'hello' }, function (err) {})
     
    // For believers
    await example.clear()

    Background

    subleveldown separates a levelup database into sections - or sublevels from here on out. Think SQL tables, but evented, ranged and realtime!

    Each sublevel is a levelup of its own. This means it has the exact same interface as its parent database, but its own keyspace and events. In addition, sublevels are individually wrapped with encoding-down, giving us per-sublevel encodings. For example, it's possible to have one sublevel with Buffer keys and another with 'utf8' encoded keys. The same goes for values. Like so:

    sub(db, 'one', { valueEncoding: 'json' })
    sub(db, 'two', { keyEncoding: 'binary' })

    There is one limitation, however: keys must encode to either strings or Buffers. This is not likely to affect you, unless you use custom encodings or the id encoding (which bypasses encodings and thus makes it your responsibility to ensure keys are either strings or Buffers). If in that case you do pass in a key that is not a string or Buffer, it will be irreversibly converted to a string.

    Authored by @mafintosh and inspired by level-sublevel by @dominictarr, subleveldown has become an official part of Level. As level-sublevel is no longer under active development, we recommend switching to subleveldown to get the latest and greatest of the Level ecosystem. These two modules largely offer the same functionality, except for hooks and per-batch prefixes.

    API

    subdb = sub(db[, prefix][, options])

    Returns a levelup instance that uses subleveldown to prefix the keys of the underlying store of db. The required db parameter must be a levelup instance. Any layers that this instance may have (like encoding-down or subleveldown itself) are peeled off to get to the innermost abstract-leveldown compliant store (like leveldown). This ensures there is no double encoding step.

    The prefix must be a string. If omitted, the effective prefix is two separators, e.g. '!!'. If db is already a subleveldown-powered instance, the effective prefix is a combined prefix, e.g. '!one!!two!'.

    The optional options parameter has the following subleveldown specific properties:

    • separator (string, default: '!') Character for separating sublevel prefixes from user keys and each other. Must sort before characters used in prefixes. An error will be thrown if that's not the case.
    • open (function) Optional open hook called when the underlying levelup instance has been opened. The hook receives a callback which must be called to finish opening.

    Any other options are passed along to the underlying levelup and encoding-down constructors. See their documentation for further details.

    Install

    With npm do:

    npm i subleveldown -S
    

    Contributing

    Level/subleveldown is an OPEN Open Source Project. This means that:

    Individuals making significant and valuable contributions are given commit-access to the project to contribute as they see fit. This project is more like an open wiki than a standard guarded open source project.

    See the Contribution Guide for more details.

    Donate

    To sustain Level and its activities, become a backer or sponsor on Open Collective. Your logo or avatar will be displayed on our 28+ GitHub repositories and npm packages. 💖

    Backers

    Open Collective backers

    Sponsors

    Open Collective sponsors

    License

    MIT © 2014-present Mathias Buus and Contributors.

    Keywords

    Install

    npm i subleveldown

    DownloadsWeekly Downloads

    30,410

    Version

    5.0.1

    License

    MIT

    Unpacked Size

    55.7 kB

    Total Files

    11

    Last publish

    Collaborators

    • avatar
    • avatar
    • avatar