subleveldown
Split a
levelup
database into sublevels with their own keyspace, encoding and events.
Table of Contents
Click to expand
Usage
If you are upgrading: please see UPGRADING.md.
const sub = require('subleveldown')
const level = require('level')
const db = level('db')
const example = sub(db, 'example')
const 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 () {
// Prints { key: 'hi', value: 'welt' }
nested.createReadStream().on('data', console.log)
})
})
Or with promises and iterators:
await example.put('hello', 'world')
await nested.put('hi', 'welt')
for await (const [key, value] of nested.iterator()) {
// Prints ['hi', 'welt']
console.log([key, value])
}
Sublevels see their own keys as well as keys of any nested sublevels:
// Prints:
// { key: '!nested!hi', value: 'welt' }
// { 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) {})
// With promises
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 underlyinglevelup
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
Support us with a monthly donation on Open Collective and help us continue our work.