Read from an abstract-level database using Node.js streams
npm install level-read-streamRead from an abstract-level database using Node.js streams.
> :pushpin: To instead consume data using Web Streams, see level-web-stream.
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_If you are migrating from levelup or level <= 7: please see UPGRADING.md._
``js
const { EntryStream } = require('level-read-stream')
const { Writable, pipeline } = require('readable-stream')
await db.put('a', '1')
await db.put('b', '2')
await db.put('c', '3')
const src = new EntryStream(db, {
gte: 'b'
})
const dst = new Writable({
write (entry, _, next) {
console.log('%s: %s', entry.key, entry.value)
next()
}
})
pipeline(src, dst)
`
Yields:
`
b: 2
c: 3
To only read keys or values rather than entries:
`js
const { KeyStream, ValueStream } = require('level-read-stream')
pipeline(new KeyStream(db), new Writable({
write (key, _, next) {
console.log(key)
next()
}
}))
`
With npm do:
`
npm install level-read-stream
Usage from TypeScript also requires npm install @types/readable-stream.
Create a readable stream that will yield entries. An entry is an object with key and value properties. The db argument must be an abstract-level database. The optional options object may contain:
- highWaterMark (number): the maximum number of entries to buffer internally before ceasing to read further entries. Default 1000.
Any other options are forwarded to db.iterator(options). The stream wraps that iterator. If you prefer to consume entries with for await...of then it's recommended to directly use db.iterator(). In either case, most databases will read from a snapshot (thus unaffected by simultaneous writes) as indicated by db.supports.snapshots.
Upon stream end or having called stream.destroy() the underlying iterator will be closed after which a close event is emitted on the stream.
Same as EntryStream but yields keys instead of entries, using db.keys() instead of db.iterator(). If only keys are needed, using KeyStream may increase performance because values won't have to be fetched.
Same as EntryStream but yields values instead of entries, using db.values() instead of db.iterator(). If only values are needed, using ValueStream may increase performance because keys won't have to be fetched.
An instance of EntryStream, KeyStream or ValueStream has the following special properties.
#### stream.db
A read-only reference to the database that this stream is reading from.
Level/read-stream` 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.
Support us with a monthly donation on Open Collective and help us continue our work.
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