level-transaction

Transactions, commits and rollbacks for leveldb/levelup databases.

NB: This module is still under active development and is not to be used in production

Installation

This module is installed via npm:

$ npm install level-transaction

Example Usage

var level = require('level');
var levelTransaction = require('level-transaction');
var db = level('/my/db/path');

// add transaction methods
db = levelTransaction(db);

// Commit a put transaction
db.txPut('key 1', 'value 1', function (err, tx) {
  if (err) throw err;
  tx.commit(function (err) {
    if (err) throw err;
    // transaction is now written
    // key 1 => value 1
  });
});

// Rollback a put transaction
db.txPut('key 1', 'value 1', function (err, tx) {
  if (err) throw err;
  tx.rollback(function (err) {
    if (err) throw err;
    // transaction is rolled back
    // key 1 doesn't exist
  });
});

// Rollback a batch transaction
db.txBatch([{ type: 'put', key: 'k1', value: 'v2' },
            { type: 'del', key: 'k2'} ],
  function (err, tx) {
    if (err) throw err;
    tx.rollback(function (err) {
      if (err) throw err;
      // transaction has been rolled back
      // k1 doesn't exist, k2 (if it existed before), still exists
    });
  });

db API

db#txPut(key, value[, opts][, callback])

Put the key, value pair to the database, but wrapped in a transaction.

The callback (unlike with the standard levelup API) will also return a tx parameter which has a commit and rollback method on it.

Any txPut operations will block any other txPut, txGet, txDel, and txBatch operations where the keys intersect with the key being written for this txPut operation.

db#txGet(key, value[, opts][, callback])

Gets the key from the database.

However, unlike a normal levelup get, a txGet will block and wait for any preceding txPut, txDel, txBatch operations that also contain the key that is being fetched by txGet.

NB: normal #get operations do not have this blocking behaviour. If you wish to have your gets wait for writes, then use #txGet and not #get.

db#txDel(key[, opts][, callback])

Delete the key key from database, but wrapped in a transaction.

The callback (unlike with the standard levelup API) will also return a tx parameter which has a commit and rollback method on it.

Any txDel operations will block any other txPut, txGet, txDel, and txBatch operations where the keys intersect with the key being written for this txPut operation.

db#txBatch(opArray,[, opts][, callback])

Executes the array opArray of levelup operations wrapped in a single transaction.

The callback (unlike with the standard levelup API) will also return a tx parameter which has a commit and rollback method on it.

Any txBatch operations will block any other txPut, txGet, txDel, and txBatch operations where the keys intersect with the key being written for this txPut operation.

transaction object API

The transaction object gets returned as a second parameter in the callbacks of db#txPut, db#txDel, and db#txBatch.

tx#commit([callback])

The callback is a standard node.js callback which takes an err object as it's first parameter. When you are executing in the body of the commit function you are guaranteed to have your transaction committed to the database.

tx#rollback([callback])

The callback is a standard node.js callback which takes an err object as it's first parameter. When you are executing in the body of the commit function you are guaranteed to have your transaction rolled back to the state of the database prior to the transaction.