Awesome
level-updater
Pseudo-atomic update methods for levelup. Started out as level-inc, but this is more useful.
Why? If you're making a lot of changes dependent on the current value of a
key, you'll find the gap between a get
and a put
becomes important:
for (var i = 0; i < 100; i += 1) {
db.get('a-key', function(err, val) {
val = parseInt(val || 0, 10)
val += 1
db.put('a-key', val)
})
}
The above example will probably result in a-key
being set to 1 and staying
there. level-updater
keeps track of overlapping calls like this and handles
them cleanly for you.
Installation
npm install level-updater
Usage
require('level-updater')(db, updater)(key, [param], [callback])
When initializing:
db
is the levelup instance to plug into.updater
is the method used to update each time a value is hit.
And for each call:
key
is the key to update.param
is an optional parameter for passing toupdater
.callback
is called after the new value has been stored in the database.
Take this example for incrementing numbers:
var db = require('levelup')(__dirname + '/db')
var update = require('level-updater')
var counter = 0
db.inc = update(db, function(value, param, key) {
return (value | 0) + param
})
for (var i = 0; i < 200; i += 1) {
db.inc('some-key', 10, function() {
counter += 1
if (counter !== 200) return
db.get('some-key', function(err, val) {
// val === "2000"
})
})
}
And this for merging JSON objects:
var db = require('levelup')(__dirname + '/db')
var update = require('level-updater', {
valueEncoding: 'json'
})
db.merge = update(db, function(original, merger) {
return Object.keys(param).reduce(function(current, key) {
current[key] = param[key]
return current
}, value || {})
})
db.merge('doc', { hello: 'world' })
db.merge('doc', { lorem: 'ipsum' }, function(err) {
db.get('doc', function(err, val) {
// val === { hello: 'world', lorem: 'ipsum' }
})
})