A database abstraction layer.

npm install enginemill-db
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Enginemill DB

Enginemill DB is a database abstraction layer for Node.js applications. We use it internally at the Fireworks Project as a plugin to our Enginemill web development framework.

The abstraction created by Enginemill DB treats the underlying database as a collection of JSON documents. It supports get, set, remove, and query methods to operate on the database. However, it does not provide a way to create the indexes needed to support the query method, so the indexes must already be created through outside channels.

Currently CouchDB is the only supported underlying database engine.


Enginemill DB is designed to be installed by including it in the package.json dependencies list for your web project. Follow the npm documentation for package.json if you don't already know how to do that.

Once you have it listed in the package.json for your project, just run

npm install

from the root of your project.


Load Enginemill DB into a Node.js module by requiring it.

    var EDB = require('enginemill-db');

Create a database API by creating a connection. In the case of CouchDB it looks like this:

    var db = EDB.connect({
      hostname: 'localhost'
    , port: 5984
    , secure: false
    , database: 'my_database'

The connect() docs:


::connect(aOpts) Create a database connection.

  • aOpts - An options Object hash
  • aOpts.hostname - The String hostname of the CouchDB server.
  • aOpts.port - The port Number to use (default: 5984 if aOpts.secure is
             false, and 443 if it is true).
  • aOpts.database - The String database name to use.
  • aOpts.secure - A boolean flag to indicate the connection should be
          secure (default: false).
  • aOpts.creds - An credentials Object hash.
  • aOpts.creds.username - The username String.
  • aOpts.creds.password - The password String.

Throws Error objects with code 'INVPARAM' if any invalid parameters are passed or required parameters are missing.

Returns a Database API instance.

Database API

Once you have a database connection, you can start using the API. All functions return a Promise object from the Q module. Use the examples below and the Q documentation to learn how to use Promises to master of the Node.js asynchronous environment.


get(aId) Fetch a document from the database.

  • aId - The id String of the document to get.

Returns a Q::Promise Object which resolves to an Object representation of the document. If the document does not exist in the database then the promise will resolve to null.

    var docId = 'abc123';

    function success(document) {
        if (document) {
            console.log('got document', document);
        } else {
            console.log('document is not in the DB');

    function failure(err) {
        console.error('Unexpected Database error:');

    db.get(docId).then(success, failure);


set(aDoc) Save a document to the database.

  • aDoc - The JavaScript Object representing the document.

Returns a Q::Promise Object which resolves to a new Object representation of the document. The promise will reject if there is a conflict error.

function myTransaction() {
    var doc = {
      first_name: 'John'
    , last_name: 'Doe'
    , age: 44
    , _id: 'abc123'

    function success(document) {
        console.log('Saved document.');

    function failure(err) {
        if (err.code === 'CONFLICT') {
            console.log('Document conflict error. Trying again.');
        } else {
            console.error('Unexpected Database error:');

    return db.set(doc).then(success, failure);


remove(aId) Delete a document from the database.

  • aId - The id String of the document to delete.

If the document has not been fetched with .get() or query() then an Error with code 'INVPARAM' will be thrown.

Returns a Q::Promise Object which resolves to true if the document was deleted and false if it didn't exist in the first place. The promise will reject if there is a conflict error.


query(aIndex, aQuery) Query an index of documents based on a key range.

  • aIndex - The name String of the index to query.
  • aQuery - The Object hash of query parameters.
  • aQuery.key - The key to use (may be String, Number, Null, or Array).
  • aQuery.limit - The max Number of documents to include in the results.
  • aQuery.descending - A Boolean flag which can be used to reverse the
                    order of the range scan (default: false).
  • aQuery.startkey - The key to begin a range scan on
                  (may be String, Number, Null, or Array).
  • aQuery.endkey - The key to end a range scan on
                (may be String, Number, Null, or Array).

It is assumed that the index has already been created through another channel. If it hasn't, then the returned Q::Promise will reject with a 'NOTFOUND' Error.

Returns a Q::Promise Object which resolves to an Array of documents represented by JavaScript Objects.

Copyright: (c) 2012 by The Fireworks Project (http://www.fireworksproject.com)

Unless otherwise indicated, all source code is licensed under the MIT license. See MIT-LICENSE for details.

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